Patent Publication Number: US-2013237989-A1

Title: Tibial guide for knee surgery

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/888,783 filed Jul. 9, 2004, which is a continuation of U.S. patent application Ser. No. 10/191,751 filed Jul. 8, 2002 (now U.S. Pat. No. 7,104,996); which is a continuation-in-part of each of the following: U.S. patent application Ser. No. 09/976,396 filed Oct. 11, 2001 (now U.S. Pat. No. 6,770,078); U.S. patent application Ser. No. 09/941,185 filed Aug. 28, 2001 (now U.S. Pat. No. 6,702,821); U.S. patent application Ser. No. 09/566,070 filed May 5, 2000 (now U.S. Pat. No. 6,575,982); U.S. patent application Ser. No. 09/737,380 filed Dec. 15, 2000 (now U.S. Pat. No. 6,503,267); U.S. patent application Ser. No. 09/569,020 filed May 11, 2000 (now U.S. Pat. No. 6,423,063); U.S. patent application Ser. No. 09/483,676 filed Jan. 14, 2000 (now U.S. Pat. No. 6,468,289); U.S. patent application Ser. No. 09/798,870 filed Mar. 1, 2001 (now U.S. Pat. No. 6,503,277); U.S. patent application Ser. No. 09/526,949 filed Mar. 16, 2000 (now U.S. Pat. No. 6,620,181); and U.S. patent application Ser. No. 09/789,621 filed Feb. 21, 2001 (now U.S. Pat. No. 6,635,073). 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a new and improved method of performing surgery, and instruments, implants, and other surgical implements that can be used in surgery. The surgery may be of any desired type. The surgery may be performed on joints in a patient&#39;s body. The surgery may be performed on any desired joint in a patient&#39;s body. Regardless of the type of surgery to be performed, a limited incision may advantageously be utilized. 
     In some embodiments, this specification relates to limited incision partial or total knee joint replacements and revisions and is the result of a continuation of work which was previously performed in conjunction with the subject matter of U.S. Pat. No. 5,514,143. This specification also contains subject matter which relates to U.S. Pat. Nos. 5,163,949; 5,269,785; 5,549,683; 5,662,710; 5,667,520; 5,961,499; 6,059,817; and 6,099,531. Although this specification refers to knee joints, it should be understood that the subject matter of this application is also applicable to joints in many different portions of a patient&#39;s body, for example a shoulder, spine, arm, hand, hip or foot of a patient. 
     During a total or partial knee replacement or revision, an incision is made in a knee portion of a leg of the patient to obtain access to the knee joint. The incision is relatively long to enable instrumentation, such as a femoral alignment guide, anterior resection guide, distal resection guide, femoral cutting guide, and femoral anterior, posterior and chamfer resection guide to be positioned relative to a distal end portion of the femur. In addition, the incision must be relatively large to enable a tibial resection guide to be positioned relative to the proximal end portion of the tibia. 
     With known procedures of total or partial knee replacement, the incision in the knee portion of the patient is made with the leg of the patient extended (straight) while the patient is lying on his or her back. At this time, the extended leg of the patient is disposed along and rests on a patient support surface. After the incision has been made in the knee portion of the leg of the patient, the leg is flexed and a foot connected with the leg moves along the patient support surface. The knee portion of the flexed leg of the patient is disposed above the patient support surface. This results in the soft tissue in the knee being compressed against the back of the knee joint. This makes it very difficult to access posterior soft tissue to remove bone spurs (ostified), meniscus, posterior capsule, ligaments in the back of the joint, and/or any residual soft tissue or connective tissue that is blocking further flexion. 
     After the incision has been made and while the leg is flexed with the foot above the patient support surface, the surgeon cannot view arteries, nerves and veins which are sitting just posterior to the knee capsule. Therefore, a surgeon may be very reluctant, or at least very careful, of inserting instruments into the back of the knee joint to remove tissue. This may result in osteophytes, bone spurs and similar types of posterior soft tissue being left in place. 
     With known techniques, the patella is commonly everted from its normal position. When the patella is everted, the inner side of the patella is exposed and faces outward away from end portions of the femur and tibia. The outer side of the everted patella faces inward toward the end portions of the femur and the tibia. Moving the everted patella to one side of end portions of the femur and tibia tends to increase the size of the incision which must be made in the knee portion of the patient&#39;s leg. 
     After implants have been positioned in the knee portion of the patient&#39;s leg, it is common to check for flexion and extension balancing of ligaments by flexing and extending the knee portion with the foot above the support surface. If the ligaments are too tight medially or laterally, they can be released to obtain the desired tension. However, the checking of ligament balance by flexing and extending the leg of the patient, ignores rotational balancing of ligaments. Since the femoral implant is movable relative to the tibial implant, the stability of the knee joint is dependent upon balancing of the ligaments in flexion, extension, and rotation. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a new and improved method and apparatus for use in performing any desired type of surgery on a joint in a patient&#39;s body. The joint may advantageously be a knee joint. However, the method and apparatus may be used in association with surgery on other joints in a patient&#39;s body. There are many different features of the present invention which may used either together or separately in association with many different types of surgery. Although features of the present invention may be used with many different surgical procedures, the invention is described herein in conjunction with surgery on a joint in a patient&#39;s body. 
     One of the features of the present invention relates to the making of a limited incision. The limited incision may be in any desired portion of a patient&#39;s body. For example, the limited incision may be in a knee portion of a leg of a patient. The limited incision may be made while a lower portion of the leg of the patient is extending downward from the upper portion of the leg of the patient. At this time, a foot connected with the lower portion of the leg of the patient may be below a surface on which the patient is supported. The limited incision may be made while the lower portion of the leg of the patient is suspended from the upper portion of the leg or while the lower portion of the leg and/or the foot of the patient are held by a support device. After the incision has been made, any one of many surgical procedures may be undertaken. 
     It is believed that in certain circumstances, it may be desired to have a main incision of limited length and a secondary incision of even smaller length. The secondary incision may be a portal or stab wound. A cutting tool may be moved through the secondary incision. An implant may be moved through the main incision. 
     Once the incision has been made, a patella in a knee portion of the patient may be offset to one side of its normal position. When the patella is offset, an inner side of the patella faces inward toward the end portions of a femur and tibia. If desired, the patella can be cut and realigned in situ, with minimal or no subluxation. Additionally, the cutting and/or realignment can be done while the knee is in flexion, which is the natural position, rather than extension. 
     Although any one of many known surgical procedures may be undertaken through the limited incision, down sized instrumentation for use in the making of cuts in a femur and/or tibia may be moved through or part way through the incision. The down sized instrumentation may be smaller than implants to be positioned in the knee portion of the patient. The down sized instrumentation may have opposite ends which are spaced apart by a distance which is less than the distance between lateral and medial epicondyles on a femur or tibia in the leg of the patient. 
     It is contemplated that the down sized instrumentation may have cutting tool guide surfaces of reduced length. The length of the cutting tool guide surfaces may be less than the length of a cut to be made on a bone. A cut on a bone in the patient may be completed using previously cut surfaces as a guide for the cutting tool. 
     It is contemplated that at least some, if not all, cuts on a bone may be made using light or other electromagnetic radiation, such as infrared radiation, directed onto the bone as a guide. The light directed onto the bone may be in the form of a three dimensional image. The light directed onto the bone may be a beam along which a cutting or milling tool is moved into engagement with the bone. 
     There are several different orders in which cuts may be made on bones in the knee portion of the leg of the patient. It is believed that it may be advantageous to make the patellar and tibial cuts before making the femoral cuts. 
     There are many different reasons to check ligament balancing in a knee portion of the leg of a patient. Ligament balancing may be checked while the knee portion of the leg of the patient is flexed and the foot of the patient is below the support surface on which the patient is disposed. Flexion and extension balancing of ligaments may be checked by varying the extent of flexion of the knee portion of the leg of the patient. In addition, rotational stability of the ligaments may be checked by rotating the lower portion of the leg of the patient about its central axis. Balancing of ligaments may also be checked by moving the foot of the patient sideways, rotating the lower portion of the leg of the patient, and/or moving the foot anteriorly or posteriorly. 
     It is believed that it may be advantageous to utilize an endoscope or a similar apparatus to examine portions of the patient&#39;s body which are spaced from the incision. It is also contemplated that images of the knee portion of the patient&#39;s leg may be obtained by using any one of many known image generating devices other than an endoscope. The images may be obtained while the patient&#39;s leg is stationary or in motion. The images may be obtained to assist a surgeon in conducting any desired type of surgery. 
     Balancing of the ligaments in the knee portion of a patient&#39;s leg may be facilitated by the positioning of one or more transducers between tendons, ligaments, and/or bones in the knee portion. One transducer may be positioned relative to a medial side of a knee joint. Another transducer may be positioned relative to a lateral side of the knee joint. During bending of the knee joint, the output from the transducers will vary as a function of variations in tension forces in the ligaments. This enables the tension forces in ligaments in opposite sides of the knee portion to be compared to facilitate balancing of the ligaments. 
     Patellar tracking may be checked by the positioning of one or more transducers between the patella and the distal end portion of the femur. If desired, one transducer may be placed between a medial portion of the patella and the distal end portion of the femur. A second transducer may be placed between a lateral portion of the patella and the distal end portion of the femur. Output signals from a transducer will vary as a function of variations in force transmitted between the patella and femur during bending of the leg. 
     The articular surface on the patella may be repaired. The defective original articular surface on the patella may be removed by cutting the patella while an inner side of the patella faces toward a distal end portion of a femur. The step of cutting the patella may be performed while the patella is disposed in situ and is urged toward the distal end portion of the femur by connective tissue. An implant may then be positioned on the patella. 
     It is contemplated that the size of the incision in the knee or other portion of the patient may be minimized by conducting surgery through a cannula. The cannula may be expandable. To facilitate moving of an implant through the cannula, the implant may be formed in two or more portions. The portions of the implant may be interconnected when the portions of the implant have been positioned in the patient&#39;s body. Although the implants disclosed herein are associated with a patient&#39;s knee, it should be understood that the implants may be positioned at any desired location in a patient&#39;s body. 
     An implant may be positioned in a recess formed in a bone in a patient. The implant may contain biological resurfacing and/or bone growth promoting materials. The implant may contain mesenchymal cells and/or tissue inductive factors. Alternatively, the implant may be formed of one or more materials which do not enable bone to grow into the implant. 
     In accordance with one of the features of the present invention, body tissue may be moved or stretched by a device which is expandable. The expandable device may be biodegradable so that it can be left in a patient&#39;s body. The expandable device may be expanded to move and/or stretch body tissue and increase a range of motion of a joint. The expandable device may be used to stretch body tissue in which an incision is to be made. 
     An improved drape system is provided to maintain a sterile field between a surgeon and a patient during movement of the surgeon relative to the patient. The improved drape system includes a drape which extends between the surgeon and a drape for the patient. During surgery on a knee portion of a leg of a patient, the drape system extends beneath a foot portion of the leg of a patient. It is contemplated that the drape system will be utilized during many different types of operations other than surgery on a leg of a patient. 
     An implant may be movable relative to both a femur and a tibia in a leg of a patient during bending of the leg. The implant may include a single member which is disposed between and engaged by end portions of both the femur and tibia. Alternatively, the implant may include a plurality of members which are disposed in engagement with each other. If desired, one of the members of the plurality of members may be secured to a bone and engaged by a member which is not secured to a bone. The implant may be secured to soft tissue in the knee portion of the patient&#39;s leg. 
     There are many different features to the present invention. It is contemplated that these features may be used together or separately. It is also contemplated that the features may be utilized in association with joints in a patient&#39;s body other than a knee joint. For example, features of the present invention may be used in association with surgery on vertebral joints or glenoid joints. However, it is believed that many of the features may be advantageously utilized together during the performance of surgery on a patient&#39;s knee. However, the invention should not be limited to any particular combination of features or to surgery on any particular joint in a patient&#39;s body. It is contemplated that features of the present invention will be used in association with surgery which is not performed on a joint in a patient&#39;s body. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of the invention will become more apparent upon a consideration of the following description taken in connection with the accompanying drawings wherein: 
         FIG. 1  is a schematic illustration depicting extended and flexed positions of a patient&#39;s leg during performance of knee surgery in a known manner; 
         FIG. 2  is a schematic illustration depicting the manner in which a leg support is used to support an upper portion of a leg of a patient above a support surface on which the patient is disposed in a supine orientation during performance of knee surgery; 
         FIG. 3  is a schematic illustration depicting the patient&#39;s leg after a portion of a drape system has been positioned over the patient, the leg being shown in a flexed condition with the foot below the patient support surface and with an upper portion of the leg supported by the leg support of  FIG. 2 ; 
         FIG. 4  is a schematic illustration of the patient&#39;s leg of  FIGS. 2 and 3  in an extended condition and of the drape system which extends between a surgeon and the patient; 
         FIG. 5  is a schematic illustration depicting the manner in which the drape system of  FIG. 4  maintains a sterile field during movement of the surgeon relative to the patient; 
         FIG. 6  is a schematic illustration depicting the manner in which an incision is made in the knee portion of the leg of the patient when the leg is in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 7  is a schematic illustration depicting the manner in which the incision is expanded and a patella is everted with the leg of the patient extended; 
         FIG. 8  is a schematic illustration depicting the manner in which a drill is utilized to form a passage in a femur in the upper portion of the leg of the patient with the leg in the position illustrated in  FIGS. 2 and 3  and the patella offset from its normal position; 
         FIG. 9  is a schematic illustration of the positioning of a femoral alignment guide in the hole formed by the drill of  FIG. 8  with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 10  is a schematic illustration depicting the position of an anterior resection guide and a stylus relative to the femoral alignment guide of  FIG. 9  before an anterior femur cut has been made with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 11  is a schematic illustration, taken generally along the line  11 - 11  of  FIG. 10 , further illustrating the relationship of the anterior resection guide and stylus to the distal end portion of the femur; 
         FIG. 12  is a schematic illustration further illustrating the relationship of the anterior resection guide and stylus to the distal end portion of the femur; 
         FIG. 13  is a schematic illustration depicting the manner in which a cutting tool is moved along a guide surface on the anterior resection guide during making of an anterior femur cut with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 14  is a schematic illustration depicting the relationship of the femoral alignment guide to the femur after making of the anterior femur cut of  FIG. 13 , the anterior resection guide and stylus being removed from the femoral alignment guide, and the leg of the patient being in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 15  is a schematic illustration of the anterior femur cut and femoral alignment guide of  FIG. 14 ; 
         FIG. 16  is a schematic illustration depicting the manner in which the femoral alignment guide is utilized to position a distal resection guide relative to the distal end portion of the femur after making of the anterior femur cut and with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 17  is a schematic illustration depicting the manner in which a distal femur cut is made with a cutting tool after the femoral alignment guide has been removed, the leg of the patient being in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 18  is a schematic illustration depicting the relationship of the cutting tool and distal resection guide of  FIG. 17  to the femur; 
         FIG. 19  is a schematic illustration depicting the manner in which a femoral cutting guide is positioned on the distal end portion of the femur with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 20  is a schematic illustration further depicting the relationship of the femoral cutting guide to the distal end portion of the femur; 
         FIG. 21  is a schematic illustration depicting the relationship of a tibial resection guide to the proximal end portion of a tibia in the lower portion of the patient&#39;s leg after making the femoral cuts and with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 22  is a schematic illustration of the distal end portion of the femur and the proximal end portion of the tibia after making the femoral and tibial cuts with the leg of the patient in the position illustrated in  FIGS. 2 and 3  and the patella offset to one side of the incision; 
         FIG. 23  is a schematic illustration further depicting the femoral and tibial cuts of  FIG. 22 ; 
         FIG. 24  is a schematic illustration depicting the manner in which force is applied against the bottom of the patient&#39;s foot by a surgeon&#39;s knee with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 25  is a schematic illustration depicting the various directions in which the lower portion of the patient&#39;s leg can be moved relative to the upper portion of the patient&#39;s leg to expose portions of the bone at the incision in the knee portion of the patient&#39;s leg and to check ligament balancing; 
         FIG. 26  is a schematic illustration depicting the manner in which a tibial punch is positioned relative to a tibial base plate with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 27  is a schematic illustration depicting completed preparation of the tibia for a tibial tray implant with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 28  is a schematic illustration depicting positioning of a tibial bearing insert in the tibial tray of  FIG. 27  with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 29  is a schematic illustration depicting femoral and tibial implants with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 30  is a schematic illustration of an apparatus which may be utilized to move the lower portion of a patient&#39;s leg relative to the upper portion of a patient&#39;s leg when the patient&#39;s kg is in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 31  is a schematic illustration depicting the manner in which a distal resection guide is connected with a patient&#39;s femur by pins which extend through the guide and through skin in the upper portion of the patient&#39;s leg into the femur with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 32  is a schematic illustration depicting the manner in which an endoscope may be inserted through an incision in a patient&#39;s knee to inspect portions of the patient&#39;s knee which are remote from the incision with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 33  is a schematic illustration similar to  FIG. 32 , depicting the manner in which the endoscope may be inserted through the incision in the patient&#39;s knee with the leg of the patient extended; 
         FIG. 34  is a schematic illustration depicting the manner in which an imaging apparatus may be utilized to generate images of a portion of the patient&#39;s leg and the manner in which a robot may be utilized to position cutting tools or other devices relative to the patient&#39;s leg with the patient&#39;s leg in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 35  is a schematic illustration depicting the relationship of a cut line to a patella in a knee of the leg of the patient with the leg in the position illustrated in  FIGS. 2 and 3  and with the patella in the normal position; 
         FIG. 36  is a schematic illustration depicting the manner in which a cutting tool is moved relative to a guide member to cut the patella of  FIG. 35  while the patella is disposed in situ; 
         FIG. 37  is a schematic illustration depicting the manner in which a tibial alignment shaft and a tibial resection guide are positioned relative to a tibia in a lower portion of a leg of the patient with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 38  is an enlarged fragmentary view of a portion of  FIG. 37  and illustrating the construction of the tibial resection guide; 
         FIG. 39  is a schematic illustration depicting the relationship between an expandable cannula and an incision in the knee portion of one leg of the patient with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 40  is a schematic illustration depicting the relationship between two separate portions of an implant which are interconnected within the patient&#39;s body; 
         FIG. 41  is a schematic illustration depicting the relationship of transducers to a flexed knee joint of a patient when the leg of the patient is in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 42  is a schematic illustration, generally similar to  FIG. 41 , illustrating the relationship of the transducers to the knee joint when the leg of the patient is extended; 
         FIG. 43  is a schematic illustration of a distal end portion of a femur in a leg of a patient with the leg in the position illustrated in  FIGS. 2 and 3  and illustrating the relationship of an implant to a recess in the end portion of the femur; 
         FIG. 44  is a schematic sectional view depicting the manner in which a cutting tool is used to form a recess in the end portion of the femur of  FIG. 43  with the leg of the patient in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 45  is a schematic sectional view, taken generally along the line  45 - 45  of  FIG. 43  further illustrating the relationship of the implant to the recess; 
         FIG. 46  is a schematic end view of a proximal end portion of a tibia in a leg of a patient, with the leg in the position illustrated in  FIGS. 2 and 3 , illustrating the relationship of an implant to a recess in the end portion of the tibia; 
         FIG. 47  is a schematic sectional view depicting the manner in which a cutting tool is used to form the recess in the end portion of the tibia of  FIG. 46 ; 
         FIG. 48  is a schematic sectional view, taken generally along the line  48 - 48  of  FIG. 46 , further illustrating the relationship of the implant to the recess; 
         FIG. 49  is a schematic sectional view illustrating the relationship of another implant to a recess in a bone in a patient&#39;s body; 
         FIG. 50  is a schematic illustration depicting the relationship between a tibial implant and a tibia in the leg of the patient; 
         FIG. 51  is a schematic illustration depicting the relationship of expandable devices to the knee portion of a patient&#39;s leg; 
         FIG. 52  is a schematic illustration depicting the manner in which an expandable device may be positioned relative to a knee portion of a patient&#39;s leg with the patient&#39;s leg in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 53  is a schematic illustration depicting the manner in which a femoral cutting guide may be mounted on a distal end of a femur in a patient&#39;s leg with the patient&#39;s leg in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 54  is a schematic illustration of the manner in which a femoral cutting guide may be mounted on a side surface of a femur in a patient&#39;s leg with the patient&#39;s leg in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 55  is a schematic illustration depicting the manner in which light is directed onto a distal end portion of a femur with the patient&#39;s leg in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 56  is a schematic illustration depicting the manner in which light is used to guide movement of a cutting tool relative to a distal end portion of a femur with the patient&#39;s leg in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 57  is a schematic illustration depicting the manner in which a cutting tool is moved relative to a secondary incision with a knee portion of a patient&#39;s leg in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 58  is schematic illustration depicting the relationship of transducers to a patella and distal end portion of a femur with the patient&#39;s leg in the position illustrated in  FIGS. 2 and 3 ; 
         FIG. 59  is a schematic illustration depicting the relationship between a movable implant, a distal end portion of a femur, and a proximal end portion of a tibia in a knee portion of a leg of a patient; 
         FIG. 60  is a plan view of a proximal end portion of a tibia depicting the manner in which an implant may be inlaid into a tibia; 
         FIG. 61  is a schematic illustration, generally similar to  FIG. 59 , depicting the relationship between a movable implant formed by a plurality of members, a distal end portion of a femur, and a proximal end portion of a tibia in a knee portion of a leg of a patient; 
         FIG. 62  is a schematic illustration, generally similar to  FIGS. 59 and 61 , depicting the relationship between an implant formed by a movable member and a fixed member, a distal end portion of a femur, and a proximal end portion of a tibia in a knee portion of a leg of a patient; 
         FIG. 63  is a schematic illustration, generally similar to  FIG. 59 , depicting the manner in which an implant is connected with a ligament in a knee portion of a patient&#39;s leg; 
         FIG. 64  is a schematic illustration, generally similar to  FIG. 60 , depicting the manner in which an implant is connected with a joint capsule in a knee portion of a patient&#39;s leg; 
         FIG. 65  is a schematic illustration, generally similar to  FIG. 60 , depicting the manner in which a retainer holds moldable implant material in place on a proximal end portion of a tibia in the knee portion of a leg of the patient; 
         FIG. 66  is a fragmentary sectional view, taken generally along the line  66 - 66  of  FIG. 65  further illustrating the manner in which the retainer holds moldable implant material; 
         FIG. 67  is a schematic illustration depicting the manner in which an implant is provided in a knee portion of a leg of a patient to correct defects in a joint and in which an osteotomy wedge is provided to correct defects in bone alignment; 
         FIG. 68  is a schematic view of the hip region with a guide wire and cannula inserted; 
         FIG. 69  is a schematic view of the hip region with an inflatable device inserted; 
         FIG. 70A  is a side view of a bone removing instrument according to the present invention in a retracted state; 
         FIG. 70B  is a perspective view of the bone removing instrument of  FIG. 70A  in an expanded state; 
         FIG. 71  is a schematic view of the hip region with the bone remover of  FIG. 70B  inserted and removing the femoral head; 
         FIG. 72  is a schematic view of the hip region with the bone remover of  FIG. 70B  inserted and removing the acetabulum; 
         FIG. 73  is a schematic view of the hip region with a backing of an acetabular component being implanted; 
         FIG. 74A  is a sectional view of one embodiment of a liner for an acetabular component; 
         FIG. 74B  is a sectional view of another embodiment of a liner for an acetabular component; 
         FIG. 75  is a schematic illustration of a knee joint with an osteotomy performed; 
         FIG. 76  is a schematic illustration of the access created by the osteotomy of the knee joint of  FIG. 75  with the patella not shown for clarity; 
         FIG. 77  is a schematic illustration of the knee joint of  FIG. 75  with the osteotomy repaired; 
         FIG. 78  is an exploded view of a modular tibial component; 
         FIG. 79  is a schematic illustration of the modular tibial component of  FIG. 78  assembled; 
         FIG. 80  is a schematic illustration of a tibial component; 
         FIG. 81  is a schematic illustration of a tibial side-cutting jig for the tibial component of  FIG. 80 ; 
         FIG. 82  is a front view of a tibial component; 
         FIG. 83  is a schematic illustration of the tibial component of  FIG. 82  being implanted; 
         FIG. 84  is another schematic illustration of the tibial component of  FIG. 82  being implanted; 
         FIG. 85  is a side view of a patellar implant; 
         FIG. 86  is a schematic illustration of a femoral component; 
         FIG. 87  is a section illustration of the femoral component of  FIG. 86 ; 
         FIG. 88  is a schematic illustration of a knee implant; 
         FIG. 89  is an exploded perspective illustration of the total knee implant of  FIG. 88 ; 
         FIG. 90  is a schematic illustration of a tibial component of a knee implant; 
         FIG. 91  is a schematic illustration of a bicompartment femoral implant; 
         FIG. 92  is a schematic illustration of a bicompartment femoral implant and a unilateral tibial implant; 
         FIG. 93  is a schematic illustration depicting the manner in which an adjustable femoral cutting jig may be mounted on a distal end of a femur in a patient&#39;s leg; 
         FIG. 94  is a schematic illustration of a femoral cutting guide having a single cutting guide surface; 
         FIG. 95  is a schematic illustration of the femoral cutting guide of  FIG. 94  with the cutting guide surface in a different position; 
         FIG. 96  is a schematic illustration of another embodiment of a femoral cutting guide having a single cutting guide surface; 
         FIG. 97  is a schematic illustration of an implant having a reduced articulating surface area; 
         FIG. 98  is a schematic illustration showing a number of the implants of  FIG. 97  implanted in an acetabulum; 
         FIG. 99  is a schematic illustration of another implant having a reduced articulating surface area; and 
         FIG. 100  is a schematic illustration of another implant having a reduced articulating surface area. 
     
    
    
     DESCRIPTION OF SPECIFIC PREFERRED EMBODIMENTS OF THE INVENTION 
     Known Method of Performing Surgery on a Patient&#39;s Knee 
     During the performance of surgery using known methods, a patient is supported on an operating table or other support surface  52  ( FIG. 1 ). When a leg  50  of the patient is in the extended position illustrated in dashed lines in  FIG. 1 , a foot  54  connected with a lower portion  56  of the leg  50  is disposed above the support surface  52 . During an operation on a knee portion  58  of the leg  50 , the knee portion is raised and lowered relative to the support surface as the leg  50  is flexed and extended. However, the foot  54  is always disposed above the support surface  54  and may be supported by the support surface throughout the operation. 
     During this known operating procedure, an incision is made in the knee portion  58  of the leg  50  when the leg is in the extended position illustrated in dashed lines in  FIG. 1 . At this time, the foot  54  of the patient may rest on the support surface  52  or be disposed in a foot support located above the support surface. Once an incision has been formed in the knee portion  58 , the leg  50  may be flexed or bent to the position illustrated in solid lines in  FIG. 1 . 
     As the knee portion  58  is bent, the leg  50  is flexed and compresses the soft tissue of the knee portion  58  against the back of the knee joint. This makes it very difficult to access the posterior of the knee portion  58  to remove bone spurs (osteophytes), the meniscus, the posterior capsule, and/or any residual soft tissue or bone that is blocking further flexion. The catching or pinching of soft tissue in the posterior aspect of the knee portion  58  may prevent further flexion and limits the range of motion. In addition, arteries, nerves and veins are sitting just posterior of the knee joint. 
     Due to the lack of access to the posterior of the knee portion  58 , a surgeon may be very reluctant or, at least, very careful about inserting instruments blindly into the back of the knee joint to remove tissue. This may result in osteophytes, bone spurs and similar types of posterior soft tissue being left in place. 
     Cuts are made on a femur and tibia with the leg  50  in the bent or flexed condition, illustrated in  FIG. 1 . This results in the distal end portion of the femur and the proximal end portion of the tibia in the leg  50  being pressed together adjacent to the cuts. This interferes with ligament balancing. The relatively large incision which is necessary to accommodate known instrumentation systems increases time required for the patient to recover from the operation. 
     Preparation for Operation 
     It is contemplated that various features and/or combinations of features of the present invention will be utilized during surgery on different portions of a patient&#39;s body, such as a head, trunk or limbs of a patient. Although at least some of the features of the present invention are believed particularly advantageous when utilized in association with surgery on any one of the many joints in a patient&#39;s body, it is believed that the various features and/or combination of the features of the present invention are particularly advantageous when utilized in conjunction with surgery on a knee portion of a leg of a patient. It should be understood that the various features of the present invention may be use separately or in any desired combination of features. 
     Surgery on the knee portion of the patient may relate to any one of many different aspects of the knee portion, such as ligaments, tendons, articular surfaces, and/or total or partial knee replacements or revisions. Although the disclosure herein frequently refers to one particular type of knee operation, that is, a total knee replacement, features of the invention may be utilized with any desired type of surgery. It is believed that it will be apparent to a person having a knowledge of knee surgery how various features of the invention may be utilized with either a full or partial knee replacement. Therefore, there has been only minimal mention herein of how the features of the invention are applicable to partial knee replacements. 
     When knee surgery is to be performed in accordance with one of the features of the present invention, the patient  62  ( FIG. 2 ) is disposed on a support surface  64  of an operating table  66 . If desired, a patient support surface  64  other than an operating table could be used to support the patient. A lower portion  68  of a leg  70  extends downward from an upper portion  72  of the leg  70 . A foot  74  connected with the lower portion  68  of the leg  70  is disposed below the support surface  64 . The leg  70  is flexed so that a knee portion  76  of the leg is bent. 
     In accordance with another of the features of the present invention, the upper portion  72  of the leg  70  can be supported above the support surface  64  by a leg support  80  ( FIG. 2 ). The leg support  80  includes a stand or base section  82  which is connected with the operating table  66 . The leg support  80  includes a base  84  which is connected with an upper end portion of the stand  82 . The base  84  is engaged by and supports the upper portion  72  of the leg  70 . 
     A generally annular thigh holder  86  extends around the upper portion  72  of the leg  70  of the patient and is connected with the base  84  and stand  82 . The base  84  has a portion which extends along the posterior side of the upper portion  72  of the leg  70  of the patient. The base  84  supports the upper portion  72  of the leg  70  above and spaced from the support surface  64 . However, the upper portion  72  of the leg  70  could be disposed in engagement with the support surface  64  if desired. 
     The leg support  80  supports the leg  70  of the patient with a hip  88  of the patient hyperflexed at an angle of twenty to thirty degrees throughout the operation on the knee portion  76 . The leg support  80  may have a known commercial construction or may have a construction similar to that disclosed in U.S. Pat. No. 4,373,709 or U.S. Pat. No. 6,012,456. If desired, a tourniquet may be combined with the leg support  80  in a manner similar to that provided in known leg supports or in a mariner similar to that disclosed in U.S. Pat. No. 4,457,302. 
     In accordance with another feature of the invention, the lower portion  68  ( FIG. 3 ) of the leg  70  is suspended from the upper portion  72  of the leg. This enables the foot  74  and ankle portion  86  of the leg  70  of the patient to be freely moved in any direction or a combination of directions. Thus, the foot  74  and ankle portion  86  of the leg  70  of the patient can be moved anteriorly or upward (as viewed in  FIG. 3 ) to decrease the extent of flexion of the knee portion  72  or even to extend or straighten the leg  70 . 
     Alternatively, the foot  74  and ankle portion  86  may be moved posteriorly toward the operating table  66 , from the position illustrated in  FIG. 3 , to hyperflex the knee portion  72  of the leg of a patient. The foot  74  may be moved sidewardly, that is in either a lateral or medial direction. In addition, the foot  74  may be rotated about the longitudinal central axis of the lower portion  68  of the leg  70 . 
     It is contemplated that the foot  74  and ankle portion  86  may be simultaneously moved in a plurality of the directions previously mentioned. If desired, the upper portion  72  of the leg  70  of the patient may be supported on a separate section of the operating table  66 , in a manner similar to the disclosure in U.S. Pat. No. 5,007,912. 
     After a drape  90  has been positioned over the patient  62  and the operating table  66 , in the manner illustrated in  FIG. 3 , the leg  70  extends out of the drape. The drape  90  may be connected with the leg support  80  and have an opening  92  ( FIGS. 3 and 4 ) through which the leg of the patient extends. This enables the leg  70  of a patient to be moved between the extended position illustrated in  FIG. 4  and a hyperflexed position in which the foot  74  is disposed posteriorly from the position illustrated in  FIG. 3 . 
     When the leg  70  is in a hyperflexed condition, the included angle between the upper and lower portions  72  and  68  of the leg  70  is less than ninety degrees. The leg  70  may be flexed from the extended position of  FIG. 4  to a hyperflexed position by manually moving the foot  74  and an ankle portion  96  of the leg  70  relative to the operating table  66  ( FIG. 2 ) while the upper portion  72  of the leg is held by the leg support  80 . When the leg  70  is hyperflexed, a portion of the foot  74  may be disposed beneath the operating table  66  ( FIG. 2 ). 
     An improved drapery system  100  ( FIG. 4 ) includes the drape  90  and a drape  102  connected with a gown  104  on a surgeon  106 . The illustrated drape  102  is formed separately from the drape  90  and gown  104 . However, the drape  102  may be integrally formed as one piece with the drape  90 . Alternatively, the drape  102  may be integrally formed as one piece with the gown  104 . If formed integral, drape  90 , drape  102 , and/or gown  104  can be provided with a quick release mechanism, such as serrated edges, to allow surgeon  106  to rapidly tear away. Thus, drapery system  100  allows the patient to be a sterile field directly or modularly attached to the surgeon and/or an assistant. 
     Regardless of whether separate or integral, drape  90  and/or drape  102  can include attachments for surgical instruments such as suction, Bovie, arthroscopic equipment, etc. Drape  102  can have a large pouch to collect all fluid, body parts, blood, etc. so they do not drain all over the floor and are collected in an easily disposable fashion. In this regard, drape  102  can include a drain, with or without active suction, to remove fluid and other debris. 
     Drape  90  could be adhesive drape with a Betadine adhesive or a clear plastic adhesive, either with or without antimicrobial agents impregnated, which covers the skin surrounding the operative field. Drape  90  could be a two layer drape with a larger drape below which sticks to the patient or is loosely attached to the patient and a narrower surgical field drape above for two layer draping. 
     In the embodiment illustrated in  FIG. 4 , the drape  102  is formed separately from the gown  104  and the drape  90 . The drape  102  is connected to the drape  90  by suitable clamps  108 . The drape  102  is connected with the waist of the surgeon  106  by clamps  110  to the gown  104 . Rather than utilizing clamps  108  to interconnect the drapes  90  and  102 , the drapes could be interconnected by VELCRO, ties, or other known devices. Of course, similar devices could be utilized to connect the drape  102  with the gown  104  of the surgeon  106 . The connection mechanism can be chosen such that, if surgeon  106  needs to change position with respect to the patient, the connection mechanism allows re-attachment of gown  104  to various locations of drape  102 . 
     The improved drapery system  100  maintains a sterile field between the leg  70  and the surgeon  106  during movement of the surgeon relative to the patient  62 . Thus, when the surgeon is in a seated position ( FIG. 4 ) the drapery system  100  provides a sterile field which extends from the surgeon to the space beneath and adjacent to the leg  70 . When the surgeon stands ( FIG. 5 ) the drapery system  100  continues to maintain a sterile field between the surgeon and the patient. This enables the surgeon  106  to move the leg  70  of a patient during an operation without contaminating the sterile field. The draping system  100  enables the sterile field to be maintained when the patient&#39;s leg is moved between the extended position of  FIGS. 4 and 5  and a hyperflexed position in which the foot  74  of the patient is disposed beneath the operating table  66 . 
     During movement of the surgeon  106  relative to the patient, for example, between the seated position of  FIG. 4  and the standing position of  FIG. 5 , the drape  102  moves with the surgeon and maintains a sterile field. Thus, when the surgeon  106  moves toward and away from the patient, the end portion of the drape  102  connected with the surgeon also moves toward and away from the patient. As the surgeon moves toward the patient, a portion of the drape  102  between the surgeon  106  and patient is lowered. As the surgeon moves away from the patient, the portion of the drape  102  between the surgeon and patient is raised. The foot  74  connected with the leg  70  of the patient is always above the drape  102  during movement of the surgeon  106 . 
     Drape  102  and/or drape  90  has flexibility and could be provided with flexed sections or may have a large redundant area which would go down to the surgeon&#39;s knees or to the floor to maintain the sterile field. By typical sterile technique, anything below the waist level of the surgeon or the support surface is considered un-sterile. However, with drapery system  100 , if drape  102  happens to drop down to the floor, it creates a contiguous sterile field and therefore, the surgeon could retrieve dropped objects from the floor if it is contained within drape  102  or drape  90 . This could save a significant amount of money by eliminating the need to dispose of (or re-sterilize) fallen surgical instruments or implants. 
     Although the drapery system  100  has been illustrated in  FIGS. 3-5  in association with a patient&#39;s leg  70 , the drapery system may be used in association with surgery on any desired portion of a patient&#39;s body. For example, the drapery system  100  could be used to maintain a sterile field between a surgeon and patient during surgery on a trunk portion of a patient&#39;s body. Alternatively, the drapery system  100  could be used to maintain a sterile field during surgery on a head or arm portion of a patient&#39;s body. 
     Drapery system  100  can use disposable drapes or can be re-sterilizable, either in its entirety or portions thereof. Additionally, known current drape technology can be incorporated into drapery system  100 . This includes the use of disposable independent drapes, ¾ sheet, disposable adherent drapes, U-drapes, disposable adhesive drapes, Betadine drapes, VELCRO attached drapes, snap, plastic snap drapes, single piece drapes, multi-drapes, two layer drapes, clear plastic drapes, independent or attached to drapes, one piece drapes with stretchable segment for extremities, arthroscopic drapes, shoulder drapes which incorporate U-drapes, square drapes, etc. 
     In another embodiment, drapes  90 ,  102  could be configured to create a mobile field. Specifically, the drapes can be made to have a surgeon&#39;s helmet attached to it and part of gown  104  attached to it so that the surgeon would literally walk into the drape system, his hands and his face would go into the drape to create a mobile surgical field attached to the patient to create even more of a sterile field. The drapery system could have laminar flow system connected to it to create sterile air coming in and then a suction coming out so it could have unidirectional airflow to further sterilize the field. 
     The drape system could have a tent, a cover over the top of this to create a mobile surgical field so that this could be done in emergency setting such as a military field or otherwise outdoors. Because the drape system can be provided with an attachment for flowing air in and out, maintaining extremely sterile air, the drape system could also be used for organ or tissue harvesting, such as bone harvesting under an emergency situation. The drape system could have the surgeon&#39;s gown, face mask, sterilizable hood all attached as part of it. It could be unrolled as one sterile pack adhering to the patient and rolling outward and the surgeon simply walks into the drape as does the assistant. When the procedure is complete, simply roll up the drape and throw it away, thereby maintaining all potential biohazards. 
     The drape could have a sterile flap where instruments could be passed through and/or a simple opening where the assistant could deliver instruments required through this field or the drape could be a flat open sheet where the assistant could bring the instruments on top of the sterile surgical field. There also may be a separate attachment for the circulating nurse. 
     As previously noted, drape  90  and/or drape  102  may also include an abbreviated gown  104  simply with the arms, front portion of the gown. This abbreviated gown could be a portion of drape  90 ,  102  so the draping system need not extend fully down to the floor. Rather, the abbreviated gown would have arm holes so that the surgeon can put his arms through the holes and the nurse would put gloves on him once they are sterilized. A provision can be made so that at least one person has an independently moveable surgical gown. 
     Incision 
     In accordance with another feature of the present invention, a limited incision  114  ( FIG. 6 ) is formed in the knee portion  76  of the leg  70 . The incision  114  is made just medial to the patella  120 . However, the incision  114  could be disposed laterally of the patella  120 . Although the length of the incision  114  may vary depending upon the circumstances, the incision  114  will usually have a length of between about seven (7) and about thirteen (13) centimeters. However, even smaller incisions may be made when circumstances permit. 
     In one embodiment, the incision is made when the knee portion  76  of the leg is flexed and the lower portion  68  of the leg extends downward from the upper portion  72  of the leg in the manner illustrated in  FIGS. 2 and 3 . At this time, the upper portion  72  of the leg  70  is supported above the support surface  64  by the leg support  80  ( FIG. 2 ). The lower portion  68  of the leg  70  is suspended from the upper portion  72  of the leg ( FIGS. 2 and 3 ). 
     When the knee portion  76  of the leg  70  is flexed so that the lower portion  68  of the leg is suspended at an angle of approximately ninety degrees relative to the upper portion  72  ( FIGS. 2 and 3 ), the incision  114  ( FIG. 6 ) may have a length of approximately ten (10) centimeters. When the leg  70  is straightened from the flexed condition of  FIGS. 2 and 3  to the extended condition of  FIGS. 4 and 5 , the length of the incision  114  may decrease by between ten and thirty percent. Thus, in one specific instance, an incision  114  had a length of approximately eleven (11) centimeters when the leg  70  was in the flexed condition of  FIGS. 2 ,  3  and  6  and a length of slightly less than ten (10) centimeters when the leg was in the extended condition of  FIG. 5 . By making the incision  114  with the leg in a flexed condition ( FIGS. 2 ,  3 , and  6 ) and operating on the leg  70  with the leg in a flexed condition, the overall length of the incision can be reduced from the length of incisions which have previously been made in the leg when it is in the extended condition. 
     The benefits of having a smaller incision include improved cosmetic results, improved rehab, less dissection of muscle and soft tissue, and preservation of the quadriceps mechanism. 
     It is preferred to have the incision  114  located adjacent to the medial edge of the patella  120 , in the manner illustrated schematically in  FIG. 6 . However, the incision  114  could be located adjacent to the lateral edge of the patella  120  if desired. Alternatively, the incision  114  could be disposed midway between lateral and medial edges of the patella  120 . By moving the incision  114  laterally or medially away from the midline of the knee, less stress is placed on incision  114  compared to a midline incision. 
     Although it is desired to minimize the length of the incision  114 , it is contemplated that the incision may have a length of approximately twice the length of the patella. It may be desired to have the incision  114  extend from a proximal end of the tibia in the leg  70  to the epicondylar notch on the distal end portion of the femur in the leg  70 . The length and location of the incision  114  may vary depending on the size of the implants to be positioned in the knee portion  76  and the location at which the implants are to be positioned. It is believed that it may be desired to have the incision  114  be smaller than the implants even though the implants must move through the incision. The viscoelastic nature of the body tissue and mobility of the incision  114  enables the implants to be larger than the incision and still move through the incision. 
     A straight incision  114  has been illustrated in  FIG. 6 . However, the incision  114  could have a different configuration if desired. For example, the incision  114  could have an L-shaped configuration. The incision  114  could be skewed at an acute angle to a longitudinal central axis of the patella  120 . If desired, the incision  114  could have a configuration matching the configuration of either the lateral or medial edge of the patella  120 . 
     Immediately after the incision  114  is formed, the leg  70  may be moved from the flexed condition of  FIGS. 2 and 3  to the extended condition of  FIG. 5 . While the leg  70  is in the extended condition, the incision  114  ( FIG. 7 ) is elastically expanded using suitable retractors. The incision  114  can also be expanded while the leg is in the flexed condition. The retractors apply force against the viscoelastic body tissue of the knee portion  76 . The retractors have a construction similar to that disclosed in U.S. Pat. No. 5,308,349. Alternatively, a pneumatic retractor, such as is disclosed in U.S. patent application Ser. No. 09/526,949 filed on Mar. 16, 2000 by Peter M. Bonutti may be utilized to expand the incision. 
     After the incision  114  has been elastically expanded, a patella  120  and tissue on the lateral side of the incision may be everted in a manner illustrated in  FIG. 7 . Thus, the patella  120  is moved from the normal orientation of  FIG. 6  to the everted or flipped orientation of  FIG. 7 , preferably while the leg  70  of the patient is in the extended orientation of  FIG. 7 . At this time, the inner side  122  of the patella  120  is facing outward away from other bones in the knee portion  76 . The outer side of the everted patella  120  is facing inward toward other bones in the knee portion  76 . This enables the inner side  122  of the patella  120  to be examined. 
     In order to enable a relatively small incision  114  to be used for operating on bones in the knee portion  76  of the leg  70  of the patient, the patella  120  is returned back to its normal position with the inner side  122  of the patella facing inward and the outer side of the patella facing outward. As this occurs, the opening at the incision  114  contracts. The retractors are then utilized to apply force against opposite sides of the incision  114 . As this occurs, the viscoelastic body tissue is extended, the opening at the incision  114  is again expanded, and the patella  120  is pushed to the lateral side of the knee portion  76 . This moves the patella  120  to a location offset to one side of the incision  114  in a manner illustrated in  FIG. 8 . The leg  70  is then flexed to the orientation shown in  FIGS. 2 and 3 . 
     If desired, the foregoing step of inverting the patella  120  may be omitted. The patella  120  may be left in orientations in which the inner side  122  of the patella faces inward throughout the operation. If this is done, the inner side  122  of the patella  120  may be inspected by tilting the patella from its normal orientation and/or using viewing devices, such as an endoscope. Regardless of how the inner side  122  of the patella  120  is inspected, moving the patella to the offset position of  FIG. 8 , with the inner side  122  facing inward, facilitates utilization of an incision  114  having a limited length. It is contemplated that many different surgical procedures could be conducted on the knee portion  76  with the patella  120  in the offset position of  FIG. 8 . Furthermore, avoiding eversion of the patella  120  significantly reduces stress on the quadriceps/tendon complex. Applicant has found that the stress on the complex is at least 20% less compared to a procedure with eversion, thereby decreasing the risks of tearing, damage, and strain. 
     As shown in  FIG. 8 , a retractor  121  can be used to offset patella  120  and/or maintain patella  120  in the offset position. In an exemplary embodiment, retractor  121  is approximately 2-3 mm thick. Retractor  121  also holds soft tissue away to expose the bone. Accordingly, retractor  121  can include at least one hole  123  for receiving a pin  125  to secure retractor  121  to bone or other body tissue. Alternatively, a suture or wire can be threaded through hole  123  to secure retractor  121  to tissue. In another embodiment, retractor  121  includes a sharp end to hold retractor  121  to the tissue. 
     Retractor  121  can be made out of any suitable material, such as metallic materials typically used for surgical instruments. If retractor  121  is made of a polymer, it is contemplated that retractor  121  could be disposable. If this is done, retractor  121  may be partially or entirely formed of relatively inexpensive polymeric materials. As previously disclosed, the disposable retractors could be sharpened at one end like a Homan. Such a disposable retractor could be made of a polymer such as polyethylene, which may be malleable to a degree. Thus, the disposable retractor could be deformed to a desired shape to expose the joint as required and possibly pin the tissue directly through the malleable portion of the retractor to hold the soft tissue out of the way while one is working on the bone. This would allow enhanced exposure through a smaller incision, visualizing it through flexion and extension. 
     The retractors could also be a composite with some metal and some plastic with a portion of the device, flexible, malleable and locking into bone to keep the tissue out of the way while one is working on the bone. Additionally, it is contemplated that the retractors could also be heated and malleable intraoperatively. The retractors could be made of a biodegradable material and be left in position to maintain a soft tissue sleeve or exposure so as to minimize scarring the joint. Regardless of the material, the retractors could have ribs or a roughened surface to grip the tissue. The retractors could also be coupled with a balloon retractor (discussed below). 
     Femoral Procedure 
     Expansion of the incision  114  with the retractors exposes a distal end portion  124  ( FIG. 8 ) of a femur  126  in the upper portion  72  of the leg  70 . The incision  114  is movable relative to the distal end portion  124  of the femur  126  to maximize exposure of the femur through the limited length of the incision. The femur  126  is then cut to receive an implant. Although either intramedullary or extramedullary instrumentation can be utilized, intramedullary instrumentation is used in an exemplary embodiment during cutting of the femur  126 . Therefore, a drill  128  is utilized to access the intramedullary canal or marrow cavity in the femur  126 . 
     The drill  128  is utilized to form a hole  130  in the center of the intercondylar notch in the distal end portion  124  of the femur  126  in a known manner. The drill  128  is used to form the hole  130  while the leg  70  is in the orientation illustrated in  FIGS. 2 and 3 . The patella  120  is in the offset position illustrated in  FIG. 8 . At this time, the inner side  122  ( FIG. 7 ) of the patella faces toward the femur  126 . 
     An epicondylar reference guide (not shown) engages the hole in the distal end portion  124  of the femur  126  to enable a line parallel to an epicondylar axis peaks of the medial and lateral condyles to be inscribed on the distal end portion  124  of the femur  126 . At this time, the leg  70  is in the orientation illustrated in  FIGS. 2 ,  3 ,  8  and  9 . A shaft  132  ( FIGS. 9 ,  10 ,  11  and  12 ) of a femoral alignment guide  134  is then inserted into the intermedullary opening  130 . 
     The femoral alignment guide  134  is then aligned with the epicondylar line which extends parallel to the epicondylar axis through the peaks of the lateral and medial condyles on the distal end portion  124  of the femur  126 . The femoral alignment guide  134  is utilized to support an anterior resection guide  138  and stylus  140  ( FIGS. 10 ,  11  and  12 ) on the distal end portion  124  of the femur  126  in the upper portion  72  of the leg  70  of the patient. Although only the femur  126  is illustrated in  FIGS. 10 ,  11  and  12 , it should be understood that the leg  70  is in the orientation illustrated in  FIGS. 2 and 3 . The upper portion  72  of the leg  70  us supported by the leg support  80 . 
     In accordance with one of the features of the present invention, the instrumentation is down sized to enable the size of the incision  114  ( FIG. 9 ) to be minimized. The downsized instrumentation has a transverse dimension which is smaller than a transverse dimension of an implant to be placed in the knee portion  76  ( FIG. 9 ). Thus, the femoral alignment guide  134  and anterior resection guide  138  have transverse dimensions, perpendicular to a longitudinal central axis of the femur  126 , which are smaller than transverse dimensions of a femoral implant  290 , tibial bearing insert  294 , and a tibial tray  286  ( FIG. 29 ) in a direction perpendicular to the longitudinal central axis of the femur  126  ( FIG. 9 ). 
     The instrumentation extends from a center portion of the femur  126  toward one side of the femur ( FIG. 11 ). In the particular operation illustrated schematically in  FIGS. 7-12 , the incision  114  is offset to the medial side of the patella  120 . Therefore, the instrumentation is offset to the medial side of the femur  126 . However, if the incision  114  were offset to the lateral side of the patella  120 , the instrumentation would be offset to the lateral side of the femur  126 . If the incision  114  were centrally disposed relative to the femur  126 , the instrumentation would be centrally disposed relative to the femur. Thus, the instrumentation is in general alignment with the incision  114  and extends only part way across the distal end portion  124  of the femur  126 . 
     The femoral alignment guide  134  ( FIGS. 10 ,  11  and  12 ) and anterior resection guide  138  have opposite ends which are spaced apart by distance which is less than a distance between epicondyles  148  and  150  on the distal end portion  124  of the femur  126 . The distance between opposite ends  154  and  156  of the femoral alignment guide  134  is less than two thirds (⅔) of the distance between tips  144  and  146  of the lateral and medial epicondyles  148  and  150 . Similarly, a distance between an end  160  and an opposite end  162  of the anterior resection guide  138  is less than two thirds (⅔) of the distance between the tips  144  and  146  of the lateral and medial epicondyles  148  and  150 . 
     The distance between opposite ends of a known femoral alignment guide and the distance between opposite ends of a known anterior resection guide are approximately the same as or greater than the distance between the tips  144  and  146  of the lateral and medial condyles  148  and  150 . The distance between opposite ends of the known femoral alignment guide and the distance between opposite ends of the known anterior resection guide are greater than the transverse dimensions of the femoral and tibial implants  286 ,  290  and  294  ( FIG. 29 ). This known anterior resection guide and femoral alignment guide are commercially available from Howmedica Osteonics of 359 Veterans Boulevard, Rutherford, N.J. under the designation “Scorpio” (trademark) Single Axis Total Knee System. 
     The incision  114  must be large enough to enable the femoral alignment guide  134  and the anterior resection guide  138  to pass through the incision. By reducing the size of the femoral alignment guide  134  and anterior resection guide  138 , the size of the incision  114  can be reduced. Of course, reducing the size of the incision  118  reduces damage to body tissue of the patient  62 . The femoral alignment guide  134  and the anterior resection guide  138  may be larger than the incision  114 . This is because the incision  114  can be resiliently stretched and/or moved relative to the femur  126  to enable the femoral alignment guide  134  and anterior resection guide  138  to move through the incision. 
     The distance between opposite ends  154  and  156  of the femoral alignment guide  134  is less than the distance which a femoral implant extends across the distal end portion  124  of the femur  126 . Similarly, the distance between opposite ends  160  and  162  of the anterior resection guide  138  is less than the distance which the femoral implant extends across the distal end portion  124  of the femur  126 . The femoral alignment guide  134  and the anterior resection guide  138  both extend medially from a center portion of the femur  126 . However, if the incision  114  were offset laterally of the patella  120 , the femoral alignment guide  134  and the anterior resection guide  138  would extend laterally from the center portion of the femur  126 . Similarly, if the incision  114  was centered relative to the patella  120 , the femoral alignment guide  134  and anterior resection guide  138  would be centered relative to the femur  126 . 
     If leg  70  is positioned as shown in  FIGS. 2 and 3 , positioning of the femoral alignment guide  134  and anterior resection guide  138  on the distal end portion  124  of the femur  126  is facilitated by distracting the knee joint under the influence of the weight of the lower portion  68  of the patient&#39;s leg and the foot  74 . Thus, when the femoral alignment guide  134  and anterior resection guide  138  are positioned on the distal end portion  124  of the femur  126 , the lower portion  68  of the leg  70  can be suspended from the upper portion  72  of the leg. At this time, the foot  74  is below the level of the support surface  64  ( FIG. 2 ) on which the patient is disposed in a supine orientation. The upper portion  72  of the patient&#39;s leg  70  is supported above the support surface  64  by the leg support  80  ( FIG. 2 ). 
     By distracting the knee joint under the influence of the weight of the lower portion  68  of the leg of the patient, the distal end portion  124  of the femur  126  is exposed through the relatively small incision  114  ( FIG. 9 ). Exposure of the distal end portion  124  of the femur  126  at the limited incision  114  is promoted by moving the lower portion  68  of the leg  70  and the incision relative to the femur. In addition, exposure of the distal end portion  124  of the femur  126  is promoted by having the patella  120  offset to the lateral side of its normal position. The inner side  122  of the patella  120  faces inward toward the distal end portion  124  of the femur  126  so that the skin on the knee portion  76  is not excessively stretched by everting the patella. 
     In accordance with another feature of the present invention, the instrumentation is at least partially positioned between the distal end portion  124  of the femur  126  and body tissue of the knee portion  76  ( FIG. 9 ). To enable the size of the incision  114  to be minimized, the instrumentation is moved laterally of the incision so that a portion of the instrumentation moves between the knee capsule and the end portion  124  of the femur  126 . This results in a portion of the instrumentation being exposed at the incision  114  and a laterally extending portion of the instrumentation being concealed by body tissue. For example, the end  154  ( FIG. 11 ) of the femoral alignment guide  134  and/or the end  160  of the anterior resection guide  138  are overlaid by body tissue adjacent to the lateral edge portion of the incision  114 . The body tissue which overlies portions of the instrumentation may include skin, the knee capsule, and connective and soft tissues. 
     With prior art instrumentation, the soft tissue must be completely dissected so that the distal end portion  124  of the femur  126  is fully exposed. In contrast, the instrumentation of the present invention can be at least partially positioned between the distal end portion  124  of the femur  126  and body tissue of the knee portion  76  ( FIG. 9 ). As discussed in more detail below, the soft tissue can be lifted or otherwise retracted. This minimizes the need for dissection. 
     When the femoral alignment guide  134  and anterior resection guide  138  are connected with the femur  126 , central axis of the femoral alignment guide and anterior resection guide are medially offset from the central axis of the femur. Thus, the central axis of the femur  216  extends through a lateral portion, that is, left portion as viewed in  FIG. 11 , of the femoral alignment guide  134 . The anterior resection guide  138  is almost entirely offset to the right (as viewed in  FIG. 11 ) of the central axis of the femur  126 . The incision  114  is disposed along a medial edge, that is, a right edge as viewed in  FIG. 6 , of the patella  120  when the patella is in its normal or initial position. 
     By having both the incision  114  and the instrumentation medially offset relative to the femur  126 , the central portion of the instrumentation is exposed at the incision. Thus, the medial edge of the incision overlaps the medial end  156  of the femoral alignment guide  134  and the medial end  162  of the anterior resection guide  138 . Similarly, the lateral edge of the incision  114  overlaps the lateral end  154  of the femoral alignment guide  134  and the lateral end  160  of the anterior resection guide  138 . 
     In view of the foregoing, it can be seen that the leg  70  ( FIG. 3 ) of the patient  62  ( FIG. 2 ) is maintained in the position illustrated in  FIGS. 2 and 3  with the foot  74  of the patient below the support surface  64  upon which the patient is supported in a supine position during forming of the incision  114  in the knee portion  76  of the leg  70 . The upper portion  72  of the patient&#39;s leg  70  is supported above the support surface  64  by the leg support  80  ( FIG. 2 ). In addition, the leg of the patient is maintained in the position illustrated in  FIGS. 2 and 3  during connection of the femoral alignment guide  134  and anterior resection guide  138  with the distal end portion  124  of the femur  126 . 
     Once the femoral alignment guide  134  and anterior resection guide  138  have been mounted on the distal end portion  124  of the femur  126 , an anterior cut is made in the manner illustrated in  FIG. 13 , During the anterior cut, a blade  170  of a saw  172  is utilized to make a cut across anterior portions of the lateral and medial condyles. The saw blade  170  is moved along guide surface  178  ( FIGS. 11 and 12 ) on the anterior resection guide  138 . 
     The guide surface  178  extends only part way across of the end portion  124  of the femur  126  ( FIGS. 11 and 13 ). The guide surface  178  does not extend across the lateral portion of the end portion  124  of the femur  126 . This at least partially results from the fact that the incision  114  ( FIG. 6 ) is offset in a medial direction from the center of the knee portion  76 . The incision  114  extends along the medial edge portion of the patella  120  when the patella is in its normal, that is, initial, position. In addition, the large majority of the anterior resection guide  138  extends medially from the central axis of the shaft  132  of the femoral alignment guide  134  ( FIG. 11 ). By having the anterior resection guide disposed in an overlying relationship with the medial portion of the end portion  124  of the femur  126  ( FIGS. 11 and 13 ), the size of the incision  114  can be reduced. 
     When anterior portions of the lateral and medial condyles  148  and  150  ( FIGS. 10 ,  11  and  12 ) on the distal end portion  124  of the femur  126  are to be cut with the saw  172 , the blade  170  is pivoted sideways ( FIG. 13 ) so that the cutting end of the blade has an arcuate component of movement. The cutting end of the blade  170  will move along a straight path during part of the movement of the blade along the guide surface  178 . However, when the blade  170  reaches the ends of the guide surface  178 , the saw  172  is pivoted to pivot the blade and move the cutting end of the blade along a path having an arcuate configuration. This results in a generally fan shaped cut which extends only part way across the anterior side of the lateral and medial condyles on the end portion  124  of the femur. 
     The saw blade may have teeth along opposite longitudinally extending edges. The saw blade  170  and saw  172  are of the oscillating type. However, a reciprocating type saw and blade may be utilized if desired. Additionally and as later described, a milling device and associated guides can be used. 
     Due to the limited length of the anterior resection guide  138 , the saw blade  170  is moved along the guide surface  178  to only partially complete the anterior skim cut on the end portion  124  of the femur  126 . The guide surface  178  is offset to the medial side of the central axis of femur  126  ( FIG. 11 ). Therefore, the saw blade can only partially form the lateral portion of the anterior skim cut while the saw blade engages the guide surface  178 . The anterior resection guide  138  can then disconnected from the femoral alignment guide  134  ( FIGS. 14 and 15 ) and the anterior femur cut is completed. 
     During completion of the anterior femur (skim) cut, previously cut surfaces on the end portion  124  of the femur  126  can be used to guide the saw blade  170  ( FIG. 13 ). Thus, an initial portion of the anterior skim cut is made on the distal end portion  124  of the femur  126  while the saw blade  170  is moved along one or more guide surfaces on the anterior resection guide  138 . After the anterior resection guide  138  has been disconnected from the femoral alignment guide  134 , the saw blade  170  is positioned in engagement with the cut surfaces on the distal end portion  124  of the femur  126 . This is accomplished by inserting the saw blade  170  into a slot or saw kerf formed in the distal end portion  124  of the femur during the initial portion of the anterior skim cut. 
     The saw blade  170  is then moved along the previously cut surfaces on the distal end portion of the femur  126  to guide the saw blade during completion of the anterior skim cut. Utilizing cut surfaces formed during an initial portion of the anterior skim cut to guide the saw blade  170  enables the size of the anterior resection guide  138  to be minimized. Although the illustrated saw blade  170  has teeth  180  at only one end, the saw blade could also have teeth along opposite longitudinally extending edges. 
     By utilizing the anterior resection guide  138  to guide movement of the saw blade  170  during only an initial portion of forming the anterior skim cut on the distal end portion  124  of the femur  126 , the overall length of the anterior resection guide, that is, the distance between the ends  160  and  162  ( FIG. 11 ) of the anterior resection guide can be limited to a distance which is less than the distance between the epicondyles  148  and  150 . Specifically, the distance between the ends  160  and  162  of the anterior resection guide  138  is less than two thirds (⅔) of the distance between the tips  144  and  146  of lateral and medial epicondyles  148  and  150  on the distal end portion  124  of the femur  126 . By limiting the length of the anterior resection guide  138 , the size of the incision  114  can be minimized. 
     It is contemplated that the initial portion of the anterior skim cut could be made with a first cutting tool and the anterior skim cut completed with a second cutting tool. The initial portion of the anterior skim cut may be made with relatively small oscillating saw blade. The final portion of the anterior skim cut may be made with a larger reciprocating saw blade. Alternatively, a small milling cutter could be used to make the initial portion of the anterior skim cut. The final portion of the skim cut could be made with a relatively long milling cutter or saw blade. It may be desired to make the initial portion of the anterior skim cut with a chisel and to complete the anterior skim cut with either a saw blade or a milling cutter. 
     The illustrated anterior resection guide  138  has a slot which forms the guide surface  178 . This results in the saw blade  170  being captured so that the saw blade is restrained against both up and down movement (as viewed in  FIG. 11 ) relative to the anterior resection guide  138 . However, in order to reduce the size of the anterior resection guide  138 , the slot could be eliminated and the saw blade  170  moved along a flat outer side of the anterior resection guide. 
     During making of the anterior skim cut, with and without the anterior resection guide  138 , body tissue ( FIG. 9 ) overlies at least portions of the lateral and medial condyles being cut. This is due to the relatively short extent of the incision  114 . Thus, the saw blade  170  and the portion of the femur  126  being cut by the saw blade are both at least partially enclosed by body tissue overlying the femur during making of the anterior skim cut. During making of the anterior skim cut, the incision  114  is moved relative to the femur  126  to provide clearance for the saw blade. 
     After the anterior portion of the lateral and medial epicondyles have been cut away and the anterior resection guide  138  removed, a flat anterior cut surface  182  ( FIGS. 14 and 15 ) is disposed on the distal end portion  124  of the femur  126 . The anterior skim cut is made on the distal end portion  124  of the femur  126  with the patella  120  offset to one side of the incision  118  ( FIG. 14 ). The inner side of the patella  120  faces toward the distal end portion  124  of the femur  126  when the patella is in the offset position of  FIGS. 9 and 14 . 
     The flat anterior cut surface  182  ( FIG. 15 ) extends parallel to the epicondylar axis. The maximum width of the anterior cut surface  182 , as measured parallel to the epicondylar axis, is greater than the distance between opposite ends  154  and  156  ( FIG. 11 ) of the femoral alignment guide  134 . Similarly, the maximum width of the anterior cut surface  182  ( FIG. 15 ), as measured parallel to the epicondylar axis, is greater than the distance between opposite ends  160  and  162  ( FIG. 11 ) of the anterior resection guide  138 . The anterior cut surface  182  is at least partially covered by body tissue which encloses the distal end portion of the femur  126  ( FIG. 14 ). 
     During making of the anterior skim cut, the patient  62  ( FIG. 2 ) is supported in a supine position on the support surface  64 . The upper portion  72  of the leg  70  is disposed above the support surface on the leg support  80 . The lower portion  68  of the leg  70  extends downward from the support surface  64 . The foot  74  ( FIG. 3 ) of the patient is disposed below the support surface. 
     Throughout the making of the anterior skim cut and the formation of the flat anterior cut surface  182  ( FIGS. 14 and 15 ) on the distal end portion  124  of the femur  126 , the lower portion  68  of the leg  70  can be suspended from the upper portion  72  of the leg in the manner illustrated in  FIG. 3 . This results in the knee portion  76  of the leg  70  being distracted by the combined weight of the lower portion  68  of the leg and the foot  74 . At this time, the lower portion  68  of the leg  70  dangles from the upper portion  72  of the leg. If desired, a holder could be provided to engage either the foot  74  and/or the lower portion  68  of the leg  70  to maintain the foot  74  and lower portion  68  of the leg in a desired position relative to the support surface  64 . 
     Once the anterior skim cut has been completed, a distal resection guide  186  is positioned relative to the flat anterior skim cut surface  182  ( FIG. 16 ). To position the distal resection guide  186  relative to the cut surface  182 , a resection guide stand  190  is mounted on the femoral alignment guide  134  in the manner illustrated in  FIG. 16 . The distal resection guide  186  is connected with the resection guide stand  190  by rotating a locking knob  192 . The distal resection guide  186  and resection guide stand  190  may be magnetized to assure correct assembly. Since the femoral alignment guide  134  is medially offset relative to the distal end portion  124  of the femur  126 , the distal resection guide  186  is also medially offset relative to the distal end portion of the femur. 
     When the distal resection guide  186  is to be connected with the resection guide stand  190 , the distal resection guide is moved between the anterior skim cut surface  182  and body tissue overlying the anterior skim cut surface ( FIG. 14 ). Thus, due to the limited extent of the incision  114 , skin and other body tissues are disposed over the anterior skim cut surface  182 . The distal resection guide  186  slides between the anterior skim cut surface  182  and the body tissue overlying the anterior skim cut surface. A lower (as viewed in  FIGS. 16 ,  17  and  18 ) major side of the distal resection guide  186  engages the anterior skim cut surface  182 . The opposite or upper (as viewed in  FIGS. 16 ,  17  and  18 ) major side of the distal resection guide  186  is engaged by the body tissue overlying the anterior skim cut surface  182  ( FIG. 14 ). The surgeon moves the incision  114  and/or the lower portion  68  of the leg  70  relative to the distal end portion of the femur  126  to facilitate movement of the distal resection guide  186  onto the anterior skim cut surface  182 . 
     Once the distal resection guide  186  has been positioned in the desired location on the flat anterior cut surface  182 , the distal resection guide  186  is secured in place with pins  196  and  198  ( FIG. 16 ). At this time, body tissue overlies the portion of the distal resection guide  186  spaced from the distal end of the femur. The distal resection guide  186  is medially offset from a central portion of the femur  126  and is aligned with the incision  114 . The incision  114  ( FIG. 14 ) is moved relative to the distal end portion  124  of the femur  216  to enable the pins  196  and  198  to be forced into the distal end portion of the femur. 
     The femoral alignment guide  134  and resection guide stand  190  are then separated from the distal end portion  124  of the femur  126  ( FIGS. 17 and 18 ). As this is done, the resection guide stand  190  ( FIG. 16 ) is separated from the distal resection guide  186 . Separation of the resection guide stand  190  from the distal resection guide  186  is accomplished by rotating the knob  192  and moving the resection guide stand  190  upward (as viewed in  FIG. 16 ) to disconnect the guide stand  190  from the femoral alignment guide  134 . The intramedullary rod  132  and femoral alignment guide  134  are then removed from the femur  126 . The distance between opposite ends  206  and  208  of the distal resection guide  186  is less than two thirds (⅔) of the distance between tips  144  and  146  ( FIG. 11 ) of the lateral and medial epicondyles  148  and  150 . 
     The distal resection guide  186 , like the anterior resection guide  138 , is down sized to enable the distal resection guide to move into the knee portion  76  of the patient&#39;s leg  70  through a relatively small incision  114 . To enable the distal resection guide  186  to move into the incision through a relatively small incision  114 , opposite ends  206  and  208  ( FIG. 16 ) of the distal resection guide  186  are spaced apart by a distance which is less than the distance between the lateral and medial epicondyles  148  and  150  ( FIG. 11 ) on the distal end portion  124  of the femur  126 . The distance between opposite ends  206  and  208  of the distal resection guide  186  is less than the distance which a femoral implant extends across the distal end portion  124  of the femur  126 . 
     The distal resection guide  186  is offset medially relative to the distal end portion  124  of the femur  126 . The incision  114  is also medially offset relative to the distal end portion  124  of the femur  126 . This results in the central portion of the guide surface  202  being exposed through the incision  114 . The lateral and medial edges of the incision  114  overlap opposite ends  206  and  208  of the distal resection guide  186 . The incision  114  also overlaps the anterior side, that is, the upper side as viewed in  FIG. 16 , of the distal resection guide. During cutting with the saw blade  170  ( FIGS. 17 and 18 ), the incision  114  is elastically expanded with suitable retractors. 
     During making of the distal femoral cut, the saw blade  170  moves along the guide surface  202  ( FIG. 17 ) on the distal resection guide  186 . The guide surface  202  on the down sized distal resection guide  186  has a length which is less than a transverse dimension of a cut to be made in the distal end portion  124  of the femur  126 . The saw  172  may be pivoted, in a manner illustrated schematically in  FIG. 13 , adjacent to opposite ends of the guide surface  202 . This moves the cutting end of the saw blade  170  along an arcuate path to form a generally fan shaped distal femoral cut. The saw  172  may be either a reciprocating or oscillating saw. 
     Due to the reduced size of the distal resection guide  186 , the saw blade  170  ( FIGS. 17 and 18 ) is ineffective to complete the distal femoral cut while the saw blade is in engagement with the guide surface  202  ( FIGS. 16 and 17 ). Therefore, after an initial portion of the distal cut has been made by moving the saw blade  170  along the guide surface  202 , the distal resection guide  186  is disconnected from the distal end portion  124  of the femur  126  and the distal femoral cut is completed. 
     During completion of the distal femoral cut, surfaces formed during the initial portion of the distal femoral cut are effective to guide the saw blade  170 . The saw blade  170  ( FIGS. 17 and 18 ) is moved into the saw kerf or slot formed during the initial portion of the distal femoral cut. As the saw blade  170  extends the initial portion of the distal femoral cut, the saw blade slides along cut surfaces formed during the initial portion of the distal femoral cut. Thus, cut surfaces formed during movement of the saw blade  170  along the guide surface  202  are utilized to guide movement of the saw blade during completion of the distal femoral cut. 
     The initial portion of the distal femoral cut may be made with a first cutting tool and the final portion of the distal femoral cut may be made with a second cutting. For example, the initial portion of the distal femoral cut may be made with a relatively small oscillating saw blade which can be readily inserted through the incision  114  into engagement with the distal resection guide  186 . The final portion of the distal femoral cut may be made with a larger saw blade which may be of the reciprocating type. It is contemplated that the initial and/or final portion of the distal femoral cut may be made with a milling cutter. It is also contemplated that a chisel may be used to make the initial and/or final portion of the distal femoral cut. 
     When the distal femoral cut is completed, a flat distal end surface  209  extends across the distal end of the femur  126  ( FIG. 17 ). The distal end surface  209  extends perpendicular to the anterior cut surface  182 . The maximum width of the distal end surface  209 , as measured parallel to the anterior cut surface  182  and epicondylar axis, is greater than the distance between opposite ends  206  and  208  of the distal resection guide  186 . The trochlear groove of the femur extends through the distal end surface  209 . 
     The distal femoral cut can be formed with the patella  120  ( FIG. 14 ) offset to one side of the incision  114  and with the inner side  122  of the patella facing toward the distal end portion  124  of the femur  126 . In addition, the leg  70  of the patient can be in the orientation illustrated in  FIGS. 2 and 3  with the foot  74  and lower portion  68  of the leg suspended from the upper portion  72  of the leg. The upper portion  72  of the leg is supported above the support surface  64  by the leg support  80 . 
     A femoral cutting guide  210  ( FIGS. 19 and 20 ) is then positioned on the distal end portion  124  of the femur  126  and utilized to make femoral anterior, posterior and chamfer cuts in a known manner. The femoral cutting guide  210  is connected with the distal end portion  124  of the femur  126  by two pins (not shown) in a known manner. The femoral cutting guide  210  is down sized so that it has opposite ends which are spaced apart by distance which is less than a distance between the lateral and medial epicondyles  148  and  150  ( FIG. 11 ) on the distal end portion  124  of the femur  126 . The femoral cutting guide  210  is offset in a medial direction from the center of the femur  126  ( FIG. 20 ). The medially offset position of the femoral cutting guide  210  is the result of the medially offset position of the incision  114  ( FIG. 6 ). 
     The initial portion of the femoral anterior, posterior and chamfer cuts are made by moving the saw blade  170  or other cutting tool along guide surfaces on the femoral cutting guide. Due to the relatively small size of the femoral cutting guide, the cuts cannot be completed while moving the saw blade  170  or other cutting tool along guide surfaces on the femoral cutting guide. Therefore, the femoral cutting guide  210  is separated from the distal end portion  124  of the femur  126  and the cuts are completed while guiding movement of the saw blade  170  or other cutting tool with cut surfaces formed during the making of the initial portions of the femoral anterior, posterior and chamfer cuts. When the femoral anterior, posterior and chamfer cuts are completed, the distal end portion  124  of the femur  126  will have the known configuration illustrated in  FIGS. 22 and 23 . 
     The femoral cutting guide  210  ( FIGS. 19 and 20 ) may have the same construction as a femoral cutting guide which is commercially available from Howmedica Osteonics of 359 Veterans Boulevard, Rutherford, N.J. The femoral cutting guide may have the construction disclosed in U.S. Pat. No. 5,282,803 or 5,749,876. However, it is preferred to down size the known femoral cutting guides to have a distance between opposite ends which is less than two thirds (⅔) of the distance between tips  144  and  146  ( FIG. 11 ) of medial and lateral condyles  148  and  150  on the distal end portion  124  of the femur  126 . This enables the femoral cutting guide  210  to move through the incision  114 . 
     Since the femoral cutting guide  210  is down sized, initial portions of the femoral anterior, posterior and chamfer cuts are made while guiding a saw blade or other cutting tool with the femoral cutting guide. These cuts are subsequently completed utilizing previously cut surfaces to guide the saw blade  170 . To complete a cut in this manner, the saw blade  170  or other cutting tool is moved along the previously cut surfaces to guide the saw blade as the cuts are extended. 
     During the making of the initial portions of the anterior, posterior and chamfer cuts with the femoral cutting guide  210  and the subsequent completion of the cuts without the femoral cutting guide, the knee portion  76  of the leg  70  of the patient can be distracted by the weight of the lower portion  68  and foot  74  of the leg. Thus, the lower portion  68  and foot  74  of the leg  70  are suspended from the upper portion  72  of the leg in a manner illustrated in  FIGS. 2 and 3  during the making of the femoral anterior, posterior and chamfer resections. The upper portion  72  of the patient&#39;s leg  70  is supported above the support surface  64  by the leg support  80  ( FIG. 2 ). 
     By distracting the knee joint during the making of the femoral anterior, posterior and chamfer cuts, access to the distal end portion  124  of the femur  126  is promoted and the making of the cuts is facilitated. Access to the distal end portion  124  of the femur  126  is also promoted by moving the suspended lower portion  68  of the leg  70  relative to the distal end portion of the femur. The incision  114  may be moved relative to the distal end portion  124  of the femur  126  by applying force to body tissue adjacent to the incision. 
     Tibial Procedure 
     As was the case for femoral preparation, the tibial procedure can be performed with the leg  70  in the position shown in  FIGS. 2 and 3 . Since the knee portion  76  of the leg  70  is distracted, a proximal end portion  212  ( FIG. 21 ) of a tibia  214  is separated from the distal end portion  124  of the femur  126 . The foot  74  ( FIG. 3 ) may be moved posteriorly to hyperflex the knee portion  76 . This facilitates viewing of the proximal end portion  212  of the tibia  214  through the relatively small incision  114 . 
     When the knee portion  76  ( FIG. 2 ) is hyperflexed, the angle between the upper portion  72  and the lower portion  68  of the patient&#39;s leg  70  is less than ninety (90) degrees. At this time, the foot  74  is disposed posteriorly of the position illustrated in  FIG. 2 . This results in the proximal end portion  212  ( FIG. 21 ) of the tibia  214  being moved anteriorly relative to the distal end portion  124  of the femur  126 . The distal end portion  212  of the tibia  214  can then be viewed through limited incision  114 . Even though the incision  114  has a relatively short length, it is possible to move the incision relative to the proximal end portion  212  of the tibia  214 . Therefore, the entire or at least almost the entire, proximal end surface of the tibia  214  can be viewed through the incision  214 . 
     It is contemplated that an external tibial alignment guide (not shown) will be utilized to align a tibial resection guide  218  ( FIG. 21 ) with the proximal end portion  212  of the tibia  214 . The tibial alignment guide has a known construction and may be similar or the same as is commercially available from Howmedica Osteonics of 359 Veterans Boulevard, Rutherford, N.J. Alternatively, the tibial alignment guide may have the construction disclosed in U.S. Pat. No. 5,578,039; or 5,282,803. 
     Once the tibial resection guide  218  ( FIG. 21 ) has been aligned with and secured to the proximal end portion  212  of the tibia  214 , the external tibial alignment guide (not shown) is disconnected from the tibial resection guide  218 . The tibial resection guide  218  is secured to the proximal end portion  212  of the tibia  214  by suitable pins. 
     In accordance with one of the features of the present invention, the tibial resection guide  218  is relatively small so that it can be moved through a relatively small incision  114  into engagement with the proximal end portion  212  of the tibia  214 . To facilitate moving of the tibial resection guide  218  through a relatively small incision  114 , the tibial resection guide  218  is smaller than implants  286  ( FIG. 27) and 294  ( FIG. 28 ) to be positioned on the proximal end portion  212  of the tibia  214 . The tibial resection guide  218  has a distance between opposite ends  228  and  230  ( FIG. 21 ) which is less than two thirds (⅔) of the distance between tips of lateral and medial epicondyles on the tibia  214 . Similarly, the distance between the ends  228  and  230  of the tibial resection guide  218  is less than two thirds (⅔) of the distance between tips  144  and  146  ( FIG. 11 ) of the lateral and medial condyles  148  and  150  on the femur  126 . 
     During positioning of the external tibial alignment guide and the tibial resection guide  218  ( FIG. 21 ) relative to the tibia  214  in the leg  70  of the patient, the leg  70  can be supported in the manner illustrated in  FIGS. 2 and 3 . Thus, the upper portion  72  ( FIG. 2 ) of the leg  70  is supported above the support surface  64  by the leg support  80 . The lower portion  68  of the leg  70  is suspended from the upper portion  72  of the leg. The foot  74  ( FIG. 3 ) connected with the lower portion  68  of the leg  70  is disposed below to support surface  64  ( FIG. 2 ). 
     During positioning of the tibial resection guide  218  on the proximal end portion  212  of the tibia  214 , the tibial resection guide is moved between the proximal end portion of the tibia and body tissue overlying the proximal end portion of the tibia. The tibial resection guide  218  is positioned relative to the proximal end portion  212  of the tibia  214  while the incision  114  is resiliently expanded. The incision  114  is expanded by applying force against opposite sides of the incision with suitable retractors. The retractors may have a construction similar to the construction disclosed in U.S. Pat. No. 5,308,349. Alternatively, a pneumatic retractor, such as is disclosed in U.S. patent application Ser. No. 09/526,949 filed Mar. 16, 2000 by Peter M. Bonutti may be used to expand the incision  114 . 
     The tibial resection guide  218  is slid inferiorly, that is, downward (as viewed in  FIG. 21 ) between the proximal end portion  212  of the tibia  214  and body tissue adjacent to the proximal end of the tibia. The tibial resection guide  218  is then connected to the proximal end portion  212  of the tibia  214  with suitable pins. Once the resection guide  218  has been connected with the tibia  214 , the force applied against opposite sides of the incision  114  by retractors is interrupted and the incision contracts. As this occurs, the body tissue moves over the lower (as viewed in  FIG. 21 ) portion of the tibial resection guide  218  to further enclose the tibial resection guide. 
     The tibial resection guide  218  is medially offset relative to the proximal end portion  212  of the tibia  214 . This is because the incision  114  is medially offset relative to the proximal end portion  212  of the tibia  214 . The incision  114  extends from the proximal end portion  212  of the tibia  214  to the superior portion of the trochlear groove in the distal end portion  124  of the femur  126 . As was previously mentioned, the incision  114  and the instrumentation may be laterally offset relative to the femur  126  and the tibia  214 . 
     Once the tibial resection guide  218  ( FIG. 21 ) has been mounted on a proximal end portion  212  of the tibia  214 , a proximal tibial cut is made. The proximal tibial cut is made by moving the blade  170  of the saw  172  along a guide surface  242  on the tibial resection guide  218  ( FIG. 21 ). When the saw blade reaches an end portion of the tibial guide surface  242 , the saw  172  is pivoted to move the saw blade  170  in the manner illustrated schematically in  FIG. 16 . This pivotal movement results in the cutting end portion of the saw blade  170  having an arcuate component of movement. This results in a generally fan shaped cut being formed in the proximal end portion  212  of the tibia  214 . 
     Due to the reduced size of the tibial resection guide  218  to facilitate movement of the tibial resection guide through the incision  114 , the saw  172  can only form an initial portion of the proximal tibial cut as the saw blade  170  moves along the guide surface  242  of the tibial resection guide  218 . To complete the proximal tibial resection cut, the tibial resection guide  218  is disconnected from the tibia  214 . 
     Once the tibial resection guide  218  has been separated from the tibia  214 , the saw blade  170  is inserted into the slit or kerf made by the saw blade during the initial portion of the proximal tibial cut. The cut surfaces which were formed during an initial portion of making the proximal tibial cut on the tibia  214  are then used to guide the saw blade  170  during completion of the proximal tibial cut. Thus, the saw blade  170  is moved along surfaces formed during the making of the initial portion of the proximal tibial cut to guide movement of the saw blade during completion of the proximal tibial cut. 
     It is contemplated that different cutting tools may be utilized to make the initial and final portions of the proximal tibial cut. Thus, the saw blade  170  used to make the initial portion of the tibial cut may be a relatively small oscillating blade and the saw blade used to make the final portion of the tibial cut may be a relatively long reciprocating blade. Alternatively, the initial and/or final portion of the tibial cut may be made with a milling cutter. If desired, a chisel could be utilized to make the initial portion of the tibial cut. The incision  114  may be expanded with suitable retractors during making of the tibial cut. The retractors may have any desired construction, including the construction disclosed in U.S. Pat. No. 5,308,349. Ligaments and other body tissue adjacent to the proximal end portion  212  of the tibia  214  may be shielded with suitable surgical instruments during making of the tibial cut. 
     Upon completion of the proximal tibial cut on the proximal end portion  212  of the tibia  214 , a flat proximal tibia cut surface  246  ( FIG. 22 ) is exposed on the proximal end portion  212  of the tibia  214  through the incision  114 . The flat cut surface  246  has a maximum width, as measured along an axis extending parallel to an axis extending through central axes of the collateral ligaments, which is greater than the distance between opposite ends  228  and  230  of the tibial resection guide  218 . The distal end portion  124  of the femur  126  is also exposed through the incision  118 . 
     In order to increase exposure of the proximal end portion  212  of the tibia  214  at the incision  218 , the foot  74  and lower portion  68  of the leg  70  ( FIG. 24 ) can be moved posteriorly toward the operating table  66  ( FIG. 2 ) to hyperflex the knee portion  76  of the patient&#39;s leg  70  during the making of the proximal tibial cut. When the knee portion  76  of the leg  70  is hyperflexed, the ankle  86  is moved from a position either extending through or anterior of a vertical plane extending perpendicular to a longitudinal central axis of the upper portion  72  of the patient&#39;s leg  70  to a position disposed posteriorly of the vertical plane. Thus, as viewed in  FIGS. 2 and 24 , the ankle  86  is moved toward the left. As this occurs, an angle between a longitudinal central axis of the upper portion  72  of the patient&#39;s leg and the longitudinal central axis of the lower portion  68  of the patient&#39;s leg is decreased to an angle of less than ninety degrees. 
     Hyperflexing the patient&#39;s leg  70  moves the proximal end portion  212  ( FIGS. 22 and 23 ) of the tibia  214  anteriorly away from the distal end portion  124  of the femur  126 . At this time, the knee portion  76  of the patient&#39;s leg is distracted under the influence of the weight of the lower portion  68  of the patient&#39;s leg and the foot  74  connected with the lower portion of the patient&#39;s leg. If desired, a force pulling the lower portion of the patient&#39;s leg downward (as viewed in  FIG. 3 ) may be applied to the patient&#39;s leg to further increase the distraction of the knee portion  76  of the leg and the extent of exposure of the proximal end portion  212  of the tibia  214 . 
     By hyperflexing the knee portion  76  of the patient&#39;s leg  70  and applying a downward (as viewed in  FIG. 3 ) force against the lower portion  68  of the patient&#39;s leg, the proximal end portion  212  of the tibia  214  is delivered anteriorly that is, toward the surgeon  106  ( FIG. 24 ). Application of a downward force against the lower portion  68  of the patient&#39;s leg is effective to open the space between the proximal end portion  212  of the tibia  214  and the distal end portion  124  of the femur  126  to the maximum extent permitted by the tendons and ligaments, that is, fibrous connective tissue, interconnecting the femur and tibia. 
     This enables the posterior cruciate ligament  250  ( FIG. 23 ) to be checked. In addition, access is provided to the posterior side of the knee portion  76  of the leg  70 . The surgeon  106  ( FIG. 24 ) can manually feel the posterior portion of the knee joint. There is sufficient space between the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214  to enable the surgeon  106  to visually and tactilely check the posterior of the knee portion  76  of the patient&#39;s leg  70 . 
     Access to the posterior portion of the knee enables osteophytes, bone spurs and similar types of posterior soft tissue to be removed. This enables tissue which could block further flexion of the knee portion  76  to be removed. In addition, it is possible to check the collateral ligaments and other fibrous connective tissue associated with the knee. 
     At this time, the lower portion  68  of the leg  70  ( FIGS. 23 and 24 ) is suspended from the upper portion  72  of the leg. Therefore, the lower portion  68  of the leg  70  hangs from the upper portion  72 . The foot  74  may be supported on the surgeon&#39;s knee  252  ( FIG. 24 ) or other surface. The foot  74  is free to move in any direction relative to the knee portion  76 . By raising or lowering his or her knee  252 , the surgeon  106  can move the tibia  214  relative to the femur  126  and vary the space between the distal end of the femur and the proximal end of the tibia. 
     By varying force indicated by arrows  256  ( FIG. 25 ), the vertical extent of space between the proximal end portion  212  of the tibia  214  and the distal end portion  124  of the femur  126  ( FIGS. 22 and 23 ) can be either increased or decreased. The force  256  is varied by raising and lowering the surgeon&#39;s knee  252 . Increasing the space between the proximal end portion  212  of the tibia  214  and the distal end portion  124  the femur  126  maximizes access to the posterior of the knee portion  76 . 
     By moving the lower portion  68  of the leg  70  upward, the ligaments and other connective tissue between the tibia  214  and femur  126  are relaxed. This enables the lower portion  68  of the leg  70  to be rotated about its longitudinal central axis, in a manner indicated by arrows  258  in  FIG. 25 . Rotational movement of the lower portion  68  of the leg  70  about its central axis enables the surgeon to cheek the collateral ligaments and the resistance encountered to rotation of the lower portion  68  of the leg relative to the upper portion  72 . 
     In addition, the foot  74  can be pivoted in a clockwise direction (as viewed in  FIG. 25 ) about the knee portion  76 , in the manner indicated by arrow  259  in  FIG. 25 , to increase the extent of flexion of the knee portion  76 . Alternatively, the foot  74  can be pivoted in a counterclockwise direction about the knee portion  76  to decrease the extent of flexion of the leg  70 . 
     The lower portion  68  of the leg  70  can also be moved sidewise, in the manner indicated by the arrow  260  in  FIG. 25 . When the lower portion  68  of the leg  70  is moved in the manner indicated by the arrow  260 , the lower portion of the leg is moved along a path extending through lateral and medial surfaces of the foot  74  and the lower portion  68  of the leg  70 . This enables the ligaments and other fibrous connective tissue in the leg to be checked for a range of movement. Although the incision  114  has not been shown in  FIG. 25 , it should be understood that the lower portion  68  of the leg  70  can be moved in the directions indicated by the arrows in  FIG. 25  when the knee portion  76  is in the condition illustrated in  FIGS. 22 and 23 . 
     The illustrated instrumentation can be formed of a metal which enables the instrumentation to be sterilized and reused. For example, the instrumentation could be formed of stainless steel. However, known metal instruments are relatively heavy and bulky. This substantially increases transportation expense. 
     It is contemplated that it may be desired to use the instrumentation once and then dispose of the instrumentation. If this is done, the instrumentation may be partially or entirely formed of relatively inexpensive polymeric materials. Thus, the femoral resection guide  134 , anterior resection guide  138 , distal resection guide  186 , femoral cutting guide  210 , and/or tibial resection guide  218  could be formed of inexpensive polymeric materials. If this was done, the guides could be used once and disposed of without being sterilized. In addition, the polymeric guides would weigh substantially less than metal guides. 
     Implants 
     After the distal end portion  124  of the femur  126  has been prepared and the proximal end portion  212  of the tibia  214  is prepared to receive implants ( FIGS. 22 and 23 ) and prior to insertion of the implants, any necessary work on the patella  120  may be undertaken. During work on the patella, the leg  70  of the patient may be extended and the patella  120  may be everted or flipped to the position illustrated in  FIG. 7 . The inner side or articular surface  122  of the patella  120  faces outward and is exposed. Known surgical techniques are then utilized to cut the patella  120  and position an implant on the patella in a known manner. This may be accomplished utilizing any one of many known devices and procedures, such as the devices and procedures disclosed in U.S. Pat. Nos. 4,565,192; 5,520,692; 5,667,512; 5,716,360; and/or 6,159,246. If desired any necessary work on the patella  120  may be undertaken after the femoral and tibial implants have been installed. 
     As an alternative to the above-described procedure in which patella  120  is everted or flipped to the position illustrated in  FIG. 7 , patella  120  can be resurfaced or otherwise worked upon while maintained in a substantially non-everted, anatomic position. U.S. Pat. No. 6,174,314 B1, the contents of which are incorporated herein by reference, discloses instrumentation and methods for in situ resurfacing of a patella. 
     Additionally, U.S. Pat. No. 5,163,949 and progeny, such as U.S. Pat. Nos. 6,358,266 B1, 6,277,136 B1, and 6,187,023 B1, discloses various embodiments of retractors and method of dissecting tissue. These embodiments include fluid operated retractors, mechanical retractors, and combinations thereof. The retractors and methods disclosed in this line of patents, which is incorporated herein by reference, can be used for patella procedures and/or visualization while the patella is maintained in a substantially non-everted, anatomic position. 
     Once the femoral and tibial cuts have been made and the patella repaired, femoral and tibial implants are installed in the knee portion of the leg  70 . Prior to permanently mounting of the implants in the knee portion  76  of the leg  70 , trials are conducted, in a known manner, with provisional femoral and tibial implants. The provisional femoral and tibial implants are releasably positioned relative to the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214 . As discussed in more detail below, the provisional implants (and/or instrumentation) can be made disposable and can be combined with the cutting guides or other instrumentation so that separate, dedicated provisional implants are not required. 
     The provisional implants are intended to aid the surgeon  106  in assessment of the function and balance of the various ligaments. The trials enable the surgeon  106  to observe the relationship of the provisional femoral and tibial implants relative to each other during flexion and extension of the knee portion  76  of the leg  70 . In one embodiment, the lower portion  68  of the leg  70  is suspended from the upper portion  72  of the leg ( FIGS. 2 and 3 ) during the trials with the provisional implants. Therefore, the lower portion of the leg  68  can be freely moved relative to the upper portion of the leg to check ligament balancing with the provisional implants. Since the lower portion of the leg  68  is suspended, it is possible to check for flexion and extension balancing of the ligaments and to check for rotational stability and rotational balancing of the ligaments during the trials with provisional implants. The lower portion  68  of the leg  70  can be moved with a combination of flexion or extension, rotation and sidewise movement. 
     The trials also enable the surgeon to check the manner in which the provisional implants interact with each other during flexion, extension, rotation, and sidewise movement. The manner in which the provisional femoral and tibial implants move relative to each other during combined bending and rotational movement of a patient&#39;s leg  70  enables a surgeon to check for the occurrence of excessive space or other undesirable situations between the provisional implants. During trials with provisional implants, the range of motion of the knee joint can be checked in both flexion/extension and rotation. 
     Utilizing known surgical techniques, it is very difficult, if not impossible, to check for both flexion/extension balancing, rotational balancing, and sidewise balancing during trials with provisional implants. With rotational balancing, the ligaments are balanced through multiple planes. When both flexion/extension and rotation are being checked, the surgeon can locate defects and improve the stability of the knee joint. The surgeon can assess the posterior cruciate ligament, collateral ligament balancing, and posterior capsule balancing. The surgeon can proceed with flexion/extension balancing of ligaments and rotational balancing of the ligaments. This enables the leg  70  to be examined throughout its range of motion during trials with provisional implants. 
     During an operation on the patient&#39;s leg  70 , the surgeon can apply upward force against the foot of the patient by resting the foot  74  on the surgeon&#39;s knee  252  ( FIG. 24 ) and raising the knee of the surgeon. Of course, when the foot  74  is to be lowered, the surgeon can lower the knee  252  upon which the foot  74  of the patient is resting. Alternatively, a pneumatic piston can be utilized to raise and lower the foot  74  of the patient. 
     Throughout the operation on the patient&#39;s knee  76 , the upper portion  72  of the patient&#39;s leg  70  is supported above the support surface  64  by the leg support  80 . This causes the hip of the patient to be hyperflexed by between 20 degrees and 40 degrees. Flexing of the hip by 20 degrees to 40 degrees improves rotational positioning and alignment. It also enhances the ability of the surgeon to hyperflex the knee portion  76  or to extend the knee portion during surgery. In addition, having the upper portion  72  of the patient&#39;s leg supported above the support surface  64  by the leg support  80  improves suspension of the lower portion  68  of the leg from the upper portion  72  of the leg. It is believed that the combination of suspending the lower portion  68  of the leg  70  and having the upper portion  72  of the leg supported above the support surface  64  by the leg support  80  will enhance the ability of a surgeon to check ligament balancing in flexion/extension, and rotation during trials during which provisional femoral and tibial components are temporarily connected with the distal end portion  124  of the femur  126  and with the proximal end portion  212  of the tibia  214 . 
     During a portion of the trials, the patella  120  may be in the normal position relative to the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214 . Therefore, during trials, it is possible to check tracking of the patella relative to the provisional femoral implant. This is done in order to prevent any possible interference of the patella  120  with the movement of the knee through its range of motion. 
     To install the trial femoral and tibial components, the proximal end portion  212  of the tibia  214  is prepared to receive the trial tibial implant. This is accomplished by positioning a tibial trial base plate  270  on the proximal end portion  212  of the tibia  214  ( FIG. 26 ). An alignment handle  272  is connected with the tibial trial base plate  270  to facilitate positioning of the tibial trial base plate relative to the proximal end portion  214  of the tibia. 
     The trial femoral implant (not shown) is then placed on the distal end portion  124  of the femur. This may be done in a known manner using a femoral impactor/extractor. A trial tibial bearing insert (not shown) is then mounted on the tibial trial base plate  270  in a known manner. Once this has been done, the trial provisional implants are used during conducting of trials with flexion/extension and rotational movements of the lower portion  68  of the patient&#39;s leg. When the trials are completed, the trial provisional implants are removed in a known manner. 
     After completion of the trials, the tibial trial base plate  270  is pinned to the proximal end portion  214  of the tibia. A tibial punch  274  ( FIG. 26 ) is positioned in a tibial punch tower (not shown) which is assembled onto the tibial trial base plate  270 . The tibial punch  274  is advanced relative to the tibial punch tower by impacting a mallet against the tibial punch. The foot  74  rests against the knee  252  of the surgeon during pounding of the tibial punch  274  into the tibia  214 . This results in the impaction forces being transmitted to the surgeon&#39;s knee  252  rather than to ligaments interconnecting the femur  126  and tibia  214 . 
     Once the tibial punch  274  has been advanced until it is fully seated on the base plate, the punch is removed. The tibial trial base plate  270  is then removed from the proximal end portion  214  of the tibia. Once the tibial trial base plate  270  has been removed, an opening  282  ( FIG. 27 ) formed in the proximal end portion  212  of the tibia  214  is exposed. The opening  282  has a configuration corresponding to the configuration of the tibial punch  274 . 
     A tibial tray  286  ( FIG. 27 ) forms a base portion of a tibial implant. The tibial tray  286  has a keel  288  with a configuration corresponding to the configuration of the tibial punch  274  ( FIG. 26 ) and the opening  282  ( FIG. 27 ) formed in the tibia  214 . The keel  288  ( FIG. 27 ) of the tibial tray  286  is covered with a suitable cement prior to being inserted into the opening  282 . If desired, the cement may be omitted. 
     A tibial component impactor/extractor may be used to insert the tibial tray  286  into the opening  282 . Once the tibial tray  286  has been mounted on the proximal end portion  212  ( FIG. 28 ) of the tibia  214 , a femoral component  290  ( FIG. 29 ) is mounted on the distal end portion  124  of the femur  126 . A known femoral impactor/extractor may be used to position the femoral component  290  on the distal end portion of the femur. The femoral component  290  may be provided with or without an intramedullary stem. Cement may or may not be used in association with the femoral component  290 . Once the femoral component  290  has been mounted on the distal end portion  124  of the femur  126 , a tibial bearing insert  294  ( FIGS. 28 and 29 ) is positioned in the tibial tray. 
     The femoral and tibial implants  286 ,  290 , and  294  may have any one of many known constructions. For example, the femoral and tibial implants could have the construction of a knee replacement which is commercially available from Howmedica Osteonics of 359 Veterans Boulevard, Rutherford, N.J. under the designation of “Scorpio” (trademark) total knee. Rather than being a total replacement, the femoral and tibial implants could be for a partial knee replacement. Thus, the femoral and tibial implants  286 ,  290  and  294  could have a construction which is the same as is illustrated in U.S. Pat. No. 5,514,143. The femoral and tibial implants  286 ,  290  and  294  may be of either the cemented type or the cementless types. 
     Once the femoral component  290  has been positioned on the femur  126  and the tibial tray  286  and bearing insert  294  positioned on the tibia  214 , ligament balancing is again conducted. The ligament balancing includes a check of stability of the joint in flexion, extension, and rotation. The ligament balancing check is performed with the lower portion  68  of the leg  70  suspended from the upper portion  72  of the leg. The upper portion  72  of the leg  70  is held above the support surface  64  ( FIG. 2 ) by the leg support  80  during the ligament balancing. 
     Since the lower portion  68  of the leg  70  is suspended from the upper portion  72 , in the manner illustrated in  FIGS. 2 ,  3  and  25 , the surgeon has a more natural feel of the true ligamentous structure. This is because tissues are not squashed or bunched in the back of the knee portion  76 . Since the lower portion  68  of the leg  70  is suspended from the upper portion  72  of the leg, the joint  76  is distracted without having the lower portion  68  of the leg jammed back against the upper portion  72  of the leg. With the leg suspended, a surgeon can view the tibial bearing insert  294  ( FIG. 29 ) and the femoral component  290  to determine how the femoral and the tibial implants cooperate with each other and the ligaments, tendons, joint capsule and other tissues. 
     The knee portion  76  may be flexed and extended, by moving the lower portion of the leg  70  along the path indicated by arrow  259  in  FIG. 25 . In addition, the lower portion  68  of the leg  70  may be moved sideways, that is, laterally and/or medially, as indicated by arrow  260  in  FIG. 25 , to check for the occurrence of slight openings between the tibial bearing insert  294  ( FIG. 29 ) and femoral component  290 . The lower portion  68  of the leg can also be rotated about its longitudinal central axis, in the manner indicated by the arrow  258  in  FIG. 25 . By simultaneously applying a combination of rotational, sideward, and flexion or extension motion to the lower portion  68  of the leg  70 , the surgeon can view the interaction between the tibial bearing insert  294  ( FIG. 29 ) and femoral component  290  through the entire range of movement of the leg  70 , including movement having rotational components. 
     By manually feeling resistance to flexion, rotational and/or sideward movement of the lower portion  68  of the patient&#39;s leg  70  ( FIG. 25 ), the surgeon can check the balancing of ligaments and other tissues in the knee portion  76  of the leg. In addition, the surgeon can check the manner in which relative movement occurs between the tibial bearing insert  294  and femoral component  290  ( FIG. 29 ). If a cheek of the rotational alignment of the femoral and tibial implants indicates that they are misaligned, the surgeon can change the rotational positions of the implants. If the ligaments are too tight medially or laterally, the surgeon can release the ligaments to the extent necessary. Ligaments which are too loose can be tightened. Since the lower portion  68  of the leg  70  is suspended, the surgeon can feel the effects of any ligamentous imbalance and take corrective action. 
     In contrast to the present invention, the majority of knee arthroplasties are done with the leg in a fixed position. Surgeons do not flex and extend through progressive intervals. As the above discussion illustrates, one aspect of the present invention involves controlling the position of the joint so that when the surgeon wants to work on the quadriceps mechanism the knee is in full extension. Similarly, when the surgeon wants to work on the tibia then he may be in more flexion, more toward 90-100°. The controlled positioning can be done in a leg alignment jig which allows reproducible holding positions that can be adjusted as desired. As previously noted, this can be achieved with electric motor, pneumatics, mechanical, or simple ratchets built on to a table, but allow precise positioning of the leg while surgeon goes from flexion to extension. There are existing leg holders, but these are very crude. Most surgeons simply use a sandbag and hold the leg in one position. This position is not precisely controlled, and therefore, somewhat variable. The soft tissue sleeve and relaxation is critical as one goes from flexion to extension, is more relaxed depending on which portion of the joint you want to expose, varying from flexion to extension. Certainly, quadriceps mechanism is the most relaxed in full extension, tighter against the femur in flexion. The tibia exposure may be improved in flexion, but controlling the specific amount of flexion/extension, locking this into position while the cuts are being performed sequentially and precisely is of significant value. 
     A portion of the foregoing check of ligamentous balancing may be performed with the patella  120  offset to one side of the incision  114 , in the manner illustrated in  FIG. 29 . This enables the surgeon to have a clear view of the tibial bearing insert  294  and femoral component  290  through the open incision  114 . After conducting a complete check of the ligamentous balancing with the patella  120  offset to one side of its natural position, the patella can be moved back to its natural position. 
     When the patella  120  is moved back to its natural position, the incision  114  closes so that there is little or no exposure of the tibial bearing insert  294  and femoral component  290  to the view of the surgeon. However, the surgeon  106  can move the lower portion  68  of the leg  70  with flexion/extension motion, indicated by the arrow  259  in  FIG. 25 , and/or rotational motion, indicated by the arrows  258 , or sideways motion indicated by arrows  260 . During this motion of the lower portion  68  of the leg  70 , the surgeon can check the manner in which the patella  120  interacts with the tibial and femoral implants and other tissues in the knee portion  76  of the patient&#39;s leg. By providing combinations of the foregoing rotational and flexion/extension motion of the lower portion of the leg  70 , the manner in which the patella  120 , with or without an implant thereon, tracks relative to the tibial and femoral implants can be readily checked. 
     In the foregoing description, the patella  120  was repaired after making the femoral and tibial cuts and before trials. However, it is contemplated that the patella  120  may be repaired after trials and after installation of the implants  286 ,  290  and  294 . Of course, the patella  120  may not need to be repaired and will be maintained in its original condition. 
     It is contemplated that fluid operated devices may be utilized to release ligaments or other tissue. The fluid operated devices may be utilized to apply force to tissue to move tissue relative to a bone, to expand the tissue, or to lengthen the tissue. For example, a balloon or bladder may be placed between tissue at the posterior of the knee portion  76  prior to mounting of the implants  286 ,  290  and  294 . The balloon may be inflated with gas or the bladder filled with liquid to move tissue relative to the distal end portion  124  of the femur  126  and relative to the proximal end portion  212  of the tibia  214 . The balloon or bladder may be used to move tissue before or after making of the femoral and/or tibial cuts. The balloon or bladder may be used to move tissue before or after the trial implants are positioned in the knee portion  76 . The balloon or bladder may be used to move tissue before or after the implants  286 ,  290  and  294  are positioned in the knee portion  76 . 
     The balloon or bladder may be formed of biodegradable or non-biodegradable material. If the balloon or bladder is formed of biodegradable material, it may be left in the knee portion during and after closing of the incision  114 . Of course, the biodegradable balloon or bladder will eventually be absorbed by the patient&#39;s body. In this regard, a narcotic or other medicament may be incorporated in the material in the balloon or the fluid used to expand the balloon. This provides a gradual time release of the medicament as the balloon degrades. Regardless of whether the device is biodegradable, capsular tightening and capsular tissue can be expanded or stretched. In the device is left in postoperatively, the balloon or bladder provides for hemostasis and maintenance of the soft tissue sleeve to improve flexion/extension. 
     It is contemplated that fluid operated retractors, expanders, and/or dissectors may be used to retract, expand or dissect body tissue. For example, retractors having a construction similar to any one of the constructions disclosed in U.S. Pat. No. 5,197,971 may be utilized to release tissue at locations spaced from the incision  114 . When tissue is to be released at locations where there is limited accessibility from the incision  114 , a device similar to any one of the devices disclosed in U.S. Pat. No. 5,295,994 may be utilized. It is believed that devices similar to those disclosed in U.S. patent application Ser. No. 09/526,949 filed Mar. 16, 2000 may be used in ways similar to those disclosed therein to move and/or release body tissue. 
     While the lower portion  68  of the leg  70  is suspended from the upper portion  72  of the leg and while the upper portion of the leg is held above the support surface  64  by the leg support  80 , the incision  114  in the knee portion  76  of the leg  70  is closed. Prior to closing of the incision  114 , the incision is thoroughly drained. Tissues in the knee portion  78  are then interconnected using a suture or other suitable devices. The soft tissues are closed in a normal layered fashion. 
     Review 
     With the exception of the procedure on the patella  120  ( FIG. 7 ), all of the foregoing procedures may be performed with the leg  70  of the patient in the orientation illustrated in  FIGS. 2 ,  3  and  25 . Thus, with the exception of procedures on the patella  120 , all of the foregoing procedures may be conducted with the lower portion  68  of the leg  70  suspended from the upper portion  72  of the leg. 
     The incision  114  ( FIG. 7 ) was made in the knee portion  76  of the leg  70  with the lower portion  68  of the leg suspended. Similarly, the incision  114  in the knee portion of the leg  70  was closed with the lower portion  68  of the leg suspended from the upper portion  72  of the leg. Thus, from the making of the incision  114  in the knee portion  76  of the leg  70  through the closing of the incision, the lower portion  68  of the leg is almost continuously extended downward from the upper portion  72  of the leg and the foot  74  was below the support surface  64 . In addition, the upper portion  72  of the leg was supported above the support surface  64  by the leg support  80 . Only during everting of the patella  120  ( FIG. 7 ) and resecting of the patella to receive an implant was the leg  70  of the patient in an extended or straightened orientation. However, the leg  70  of the patient could be extended or straightened at any time the surgeon desires during the foregoing procedure. 
     Throughout the entire procedure, the drapery system  100  ( FIGS. 4 and 5 ) maintained a sterile field between the surgeon  106  and the patient. As the surgeon moved between seated and standing positions and moved toward or away from the patient, the drape  102  would rise or fall. Thus, when the surgeon  106  moves from the seated position of  FIG. 4  to the standing position of  FIG. 5 , the drape  102  tends to rise upward with the surgeon. Similarly, when the surgeon moves from the standing position of  FIG. 5  back to the seated position of  FIG. 4 , the drape  102  tends to move downward. The drape  102  will tend to move upward as the surgeon moves away from the leg  70  of the patient and will tend to move downward as the surgeon moves toward the leg  70  of the patient. Although it is preferred to use the drapery system  100  illustrated in  FIGS. 4 and 5  and the various other embodiments described in connection with these figures, it is contemplated that a different drapery system could be utilized if desired. 
     It is believed that it will be particularly advantageous to utilize down sized instrumentation in performing the foregoing procedures on the knee portion  76  of the patient. The femoral alignment guide  134  ( FIGS. 10-15 ), anterior resection guide  138  ( FIGS. 10-13 ), resection guide stand  190  ( FIG. 16 ), distal resection guide  186  ( FIGS. 16-18 ), and tibial resection guide  218  ( FIG. 21 ) all have sizes which are two thirds (⅔) of their normal sizes or smaller. However, the various down sized instrumentation components of  FIGS. 9-21  can be utilized in their normal manner and have generally known constructions. Thus, the instrumentation of  FIGS. 9-21 , with the exception of being down sized, is generally similar to known instrumentation which is commercially available from Howmedica Osteonics Corp. of Rutherford, N.J. under the trademark “Scorpio” single access total knee system. 
     As was previously mentioned, it is contemplated that extramedullary and/or intramedullary instrumentation could be utilized if desired. Although it is believed that it may be preferred to use instrumentation which is anteriorly based, it is contemplated that posteriorly based instrumentation systems could be used if desired. Additionally and as described below, lateral or medial based instrumentation could be used if desired. The present invention also envisions combinations of these various instrumentations. 
     In the foregoing description, the saw  172  and blade  170  ( FIG. 15 ) were utilized to make cuts in various bones in the knee portion  76  of the leg  70  of the patient. The saw  172  and blade  170  may be of either the oscillating or reciprocating type. However, it is contemplated that other known cutting instruments could be utilized. For example, a milling device could be utilized to form at least some of the cuts. Alternatively, a laser or ultrasonic cutter could be utilized in making some of the cuts. It is believed that it may be particularly advantageous to utilize a laser or ultrasonic cutter to initiate the formation of a cut and then to utilize a saw or other device to complete the cut. 
     It is contemplated that either extramedullary or intramedullary instrumentation having a construction which is different than the illustrated construction could be utilized. For example, the anterior resection guide  138   FIGS. 10 ,  11  and  12  has a guide surface  178  which is formed by a slot through which the saw blade extends. If desired, the guide surface  178  could be provided on an end face without providing for capturing or holding of the saw blade  170  in a slot. 
     The instrumentation may be entirely or partially formed of light weight polymeric materials which are relatively inexpensive. A femoral cutting guide  210  has a size which corresponds to the size of the specific femoral component  290  which is to be installed on the distal end portion  124  of a femur  126 . An inexpensive femoral cutting guide  210 , formed of polymeric material, may be packaged along with a femoral component  290  of the same size. After the femoral component  290  is installed, the femoral cutting guide  210  may be discarded. This would minimize investment in instrumentation and would tend to reduce the cost of handling and/or sterilizing cutting guides. The result would be a reduction in cost to the patient. 
     It is contemplated that the use of guide members, corresponding to the anterior resection guide  138  of  FIG. 11 , the distal resection guide  186  of  FIG. 16 , and the tibial resection guide  218  of  FIG. 21  could be eliminated if desired. If this was done, positioning of a saw blade or other cutting device could be provided in a different manner. For example, light forming a three dimensional image, such as a hologram, could be projected onto the distal end portion  124  of the femur  126 . The three dimensional image would have lines which would be visible on the surface of the end portion  124  of the femur  126 . The saw cut would be formed along these lines. Alternatively, robot type devices having computer controls could be utilized to form the cuts without using guide members. 
     It is contemplated that emitters, receivers, and/or reflectors of computer navigation systems could be pinned or otherwise attached onto the femur  126  and tibia  214  to provide cutting positions and to facilitate ligament balancing through relatively small incisions. The computer navigation system may utilize three or four separate registers which have optical feedback to a central unit. The computer navigation system may utilize electromagnetic or photo-optical feedback. 
     It is contemplated that various known structures could be utilized in association with the leg  70  of the patient during performing of one or more of the procedures described herein. For example, the apparatus disclosed in U.S. Pat. No. 5,514,143 could be connected with the leg  70  of the patient and used to control flexion and extension of the leg. Since the apparatus disclosed in U.S. Pat. No. 5,514,143 includes separate femoral and tibial sections, it is believed that this apparatus may be particularly well adapted for use with the leg of the patient in the orientation illustrated in  FIGS. 2 ,  3  and  25 . This apparatus does not interfere with distraction of the knee portion  76  and can accommodate flexion and extension of the leg  70  of the patient. 
     The foregoing description has primarily referred to a full knee replacement. However, it is contemplated that the apparatus and procedures disclosed herein may be utilized in association with a revision or partial knee replacement. For example, the method and apparatus disclosed herein could be utilized in association with a unicompartmental knee replacement of the type disclosed in the aforementioned U.S. Pat. No. 5,514,143. The method and apparatus disclosed herein could be utilized in association with a revision of a previously installed full or partial knee replacement. It is also contemplated that the procedures disclosed herein and apparatus similar to the apparatus disclosed herein may be utilized with many different types of joints. For example, the procedures and apparatus may be utilized in association with a joint in an arm, shoulder, spine or hip of a patient. 
     Support Assembly 
     In accordance with one of the features of the invention, a support assembly  330  ( FIG. 30 ) is provided for the lower portion  68  of the leg  70  of the patient. Rather than support the foot  74  of the patient on the knee  252  of the surgeon ( FIG. 24 ), as previously described herein, the support assembly  330  may be utilized. The support assembly  330  includes a flat surface  332  which engages the foot of the patient. A pneumatically actuated piston and cylinder assembly  334  is operable to raise and lower the foot  74  of the patient in the manner indicated schematically by an arrow  336  in  FIG. 31 . Mechanisms other than pneumatics, such as a motor, could be used to control piston and cylinder assembly  334 . 
     When the knee portion  76  of the leg  70  is to be distracted, the piston and cylinder assembly is operated to lower the surface  332  and foot  74  of the patient. As this occurs, the weight transferred from the foot  74  of the patient to the support surface decreases until the support surface  332  is below and spaced from the foot  74 . Similarly, when the extent of distraction of the knee portion  76  is to be decreased, the piston and cylinder assembly  334  is operated to raise the support surface  332  and foot  74  of the patient. 
     By providing a flat support surface  332 , the lower portion  68  of the leg of the patient may be rotated about its longitudinal central axis relative to the upper portion  72  of the leg of the patient when the support assembly  330  is being utilized to at least partially support the lower portion  68  of the leg of the patient. However, it is contemplated that a foot holder could be provided in place of the flat surface  332 . The foot holder would have the advantage of being able to hold the foot  74  of the patient in a desired orientation relative to the upper portion  72  of the leg  70  of the patient. The foot holder could be constructed so as to have a pneumatically (or other) actuated drive to rotate the foot  74  about the longitudinal central axis of the leg  70  and/or lower portion  68  of the leg  70  of the patient. 
     The support surface  332  is raised and lowered by operation of the piston and cylinder assembly  334 . Therefore, operation of the piston and cylinder assembly  334  is effective to move the lower portion  68  of the leg  70  of the patient in the directions of the arrow  256  in  FIG. 25 . It is contemplated that a drive assembly could be connected with the support surface  332  to rotate the support surfaces about a vertical axis. The drive assembly may include a rack and pinion drive arrangement or a worm and wheel drive arrangement. By rotating the support surface  332  about a vertical axis relative to the piston and cylinder assembly  334 , movement of the lower portion  68  of the leg  70  in the directions of the arrow  258  in  FIG. 25  would be facilitated. 
     Percutaneous Instrumentation Mounting 
     In accordance with another feature of the invention, it is contemplated that the size of the incision  114  may be reduced by connecting one or more of the guide members with one or more bones through the skin of the patient. For example, the anterior resection guide  138  ( FIGS. 10 and 11 ), distal resection guide  186  ( FIG. 16 ), femoral cutting guide  210  ( FIGS. 19 and 20 ), and/or tibial resection guide  218  ( FIG. 21 ) could be mounted on the outside of the leg  70  and connected with bone in either the upper portion  72  or the lower portion  68  of the leg  70  of the patient. This would minimize or even eliminate the necessity of moving the guide through the incision  114  into engagement with the bone. It would also minimize or even eliminate the necessity of sizing the incision  114  so as to accommodate the guide. 
     For example, the distal resection guide  186  ( FIGS. 16-18 ) is illustrated schematically in  FIG. 31  as being mounted outside of the upper portion  72  of the leg  70  of the patient. The distal resection guide  186  is illustrated in  FIG. 31  as being disposed in engagement with an outer surface of skin  342  which encloses the distal end portion  124  of the femur  126 . The distal resection guide  186  is mounted directly outward of the flat anterior cut surface  182  formed on the distal end portion  124  of the femur  126 . The skin  342  and other body tissue extends between the distal resection guide  186  and the distal end portion  124  of the femur  126 . 
     The distal resection guide  186  is connected with the femur  126  by the pins  196  and  198 . The pins  196  and  198  extend through the distal resection guide  186  and the skin  342  into the femur  126 . The pins  196  and  198  extend through the flat anterior cut surface  182  into the femur  126  and hold the distal resection guide  186  against movement relative to the femur  126 . 
     Although a distal resection guide  186  has been illustrated in  FIG. 31 , it is contemplated that an anterior resection guide, corresponding to the anterior resection guide  138  of  FIG. 11  could be mounted in a similar manner. If this were done, the anterior resection guide  138  would have a generally L-shaped configuration with a body portion which would extend along the outer surface of the skin  342  ( FIG. 31 ). Pins, corresponding to the pins  196  and  198  of  FIG. 31 , would extend through the relatively long body portion of the generally L-shaped anterior resection guide  138 , through the skin  342  and into the femur  126 . 
     The short leg of the L-shaped anterior resection guide  138  would be positioned adjacent to the distal end portion  124  of the femur  126 . The short leg of the anterior resection guide would have a guide surface aligned with the distal end portion  124  of the femur  126  at a location corresponding to the location where the flat anterior cut surface  182  is to be formed. This guide surface could be of the slot or capture type illustrated in  FIG. 14 . Alternatively, the guide surface could be formed on a flat end face of the anterior resection guide. This would result in elimination of the slot commonly utilized to capture a saw blade or other cutting instrument. By having a portion of the anterior resection guide disposed outside of the incision  114  and connected with the femur  126  through the skin  342 , the size of the incision  114  tends to be minimized. 
     In addition to the aforementioned guides associated with the femur  126 , it is contemplated that a guide associated with the tibia  214  ( FIG. 21 ) could be connected with the tibia by pins extending through the skin  342 . For example, the tibial resection guide  218  could be placed in abutting engagement with skin which overlies the proximal end portion  212  of the tibia  214 . Suitable pins would extend through the tibial resection guide  218  ( FIG. 21 ) and through the skin  342  ( FIG. 31 ) into engagement with the distal end portion  212  of the tibia. Although it may be preferred to provide a tibial guide surface  242  of the slot type illustrated in  FIG. 22 , it is contemplated that only a single guide surface could be provided on a flat end portion of the tibial resection guide if desired. 
     Inspection 
     It is contemplated that at various times during the performance of the foregoing procedures, it may be desired to inspect locations remote from the incision  114 . Thus, it may be desired to visually ascertain the condition of soft tissue in the posterior of the knee portion  76 . In addition, it may be desired to visually check the condition of the collateral ligaments or soft tissue adjacent to the ligaments. The inspections may be conducted before or after the making of femoral and tibial cuts, before or after trials, and/or before or after installation of the implants  286 ,  290  and  294 . 
     In accordance with another feature of the invention, locations remote from the limited incision may be visually inspected. To inspect locations remote from the incision  114 , a leading end portion  350  ( FIG. 32 ) of an endoscope  352  can be inserted through the incision  114  and moved to the posterior of the knee portion  76 . Alternatively, the leading end portion  350  of the endoscope  352  can be inserted through a smaller stab wound incision. A camera  354  transmits an image to a monitor  356 . The surgeon  106  can then view images of the posterior of the knee portion  76  transmitted through the endoscope  352 . The upper portion  72  of the leg  70  is supported by the leg support  80 . The leg  70  is shown in  FIG. 32  in the same position illustrated in  FIGS. 2 and 3 . 
     In order to provide the surgeon  106  with information as to how the femoral and tibial implants  286 ,  290  and  294  interact with tissues in the knee portion  76 , the leg  70  of the patient may be bent between the flexed condition of  FIG. 32  and the extended condition of  FIG. 33 . In addition, the lower portion  68  of the leg  70  may be rotated about its longitudinal central axis, in the manner indicated by the arrow  258  in  FIG. 25 . During bending of the knee portion  76 , the surgeon views images of the posterior knee portion transmitted through the endoscope  352  to the monitor  356 . This enables the surgeon to detect any present or potential interference of tissue in the knee portion  76  with the full range of motion of the knee portion. During relative movement between the femur  126  and tibia  214 , the surgeon can view the manner in which the femoral and tibial implants interact with each other and the tissue in the joint capsule. 
     It is contemplated that the end portion  350  of the endoscope  352  will be moved so as to enable the surgeon  106  to view the collateral ligaments, particularly the ligament on the lateral side of the knee portion  76 , during bending of the knee portion. Although the endoscope  352  is illustrated in  FIGS. 32 and 33  as being utilized after the femoral and tibial implants  286 ,  290  and  294  have been connected with the femur  126  and tibia  214 , it is contemplated that the endoscope will be utilized prior to cutting of the femur and tibia, after cutting of the femur and tibia and prior to trials, after trials, and/or during trials. 
     It is contemplated that the endoscope  352  may be inserted into the knee portion  76  of the patient at a location other than through the incision  114 . Thus, if desired, a separate, very small portal or puncture type incision could be formed in the knee portion  76  of the leg of the patient at a location adjacent to a location where it is desired to visually inspect the knee portion of the patient. Although it is believed that it will be desired to inspect the knee portion  76  of the patient while there is relative-movement between the femur  126  and tibia  214 , it should be understood that the endoscope  352  could be utilized to inspect the knee portion  76  while the femur  126  and tibia  214  are stationary relative to each other. 
     Although an endoscope  352  is illustrated in  FIGS. 32 and 33 , it is contemplated that other known devices could be utilized to inspect knee portion  76 . Thus any desired fiber optic type instruments may be utilized to inspect the knee portion  76 . For example any of the known instruments associated with arthroscopic surgery could be utilized to inspect the knee portion  76 . 
     Generation of Images and Robotic Device 
     In accordance with another feature of the invention, during performance of surgery on a knee portion  76  of a patient&#39;s leg  70  ( FIG. 34 ), a known C-arm fluoroscope  360  or other imaging system is utilized to generate images of the knee portion  76  of the leg  70  during movement of the lower portion  68  of the leg relative to the upper portion of the leg. Images are transmitted in any fashion from the C-arm fluoroscope  360  to a control unit  362 . Video images are transmitted from the control unit  362  to a video screen  364  which is viewable by the surgeon  106  during surgery on the knee portion  76  of the leg  70 . A continuous display of images is projected in rapid succession on the screen illustrating the knee portion  76  of the leg  70  when the lower portion  68  of the leg is in various positions relative to the upper portion of the leg. 
     Thus, during flexion and/or extension of the leg  70 , video images are transmitted to the screen  364  to enable a surgeon to view images of the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214  during bending of the knee portion. The video display of images may be undertaken prior to forming of the incision  114  to enable the surgeon to view the manner in which components of the knee portion  76  interact prior to surgery. After the incision  114  has been made, the images provided on the video screen  364  enable the surgeon to visually determine the relationship between the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214  after the patella  120  has been moved to an offset position and prior to initiating any cuts on the bones in the patient&#39;s leg  70 . 
     After cuts have been made on the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214  in the manner previously explained, the lower portion  68  of the patient&#39;s leg can be moved relative to the upper portion  72  of the patient&#39;s leg. The images provided on the video screen  364  will enable a surgeon to better understand the relationship between the femur, tibia, and ligaments in the patient&#39;s leg during preliminary checking of ligament balancing after the distal end portion  124  of the femur  126  has been cut and after the proximal end portion  212  of the tibia  214  has been cut. 
     During trials when trial tibial and femoral components have been temporarily connected with the femur  126  and tibia  214 , the images provided at the video screen  364  will enable the surgeon to better evaluate the interaction between the trial components and body tissue in the knee portion  76  of the patient&#39;s leg  70 . Once the trials have been completed and the femoral and tibial implants  286 ,  290  and  294  positioned on the femur  126  and tibia  214 , the images provided at the video screen  364  will enable the surgeon to evaluate the relationship between the femoral and tibial implants. 
     During ligamentous balancing, images provided at the video screen  364  will indicate to the surgeon whether or not there is any undesired relative movement between the femoral and tibial implants. It is contemplated that the images be transmitted from the control unit  362  to the video screen  364  during movement of the lower portion  68  of the patient&#39;s leg  70  in any one or a combination of the directions indicated by the arrows  256 ,  258 ,  259  and  260  in  FIG. 25 . Once the surgeon, with the assistance of images provided at the video screen  364 , is satisfied that the femoral and tibial implants  286 ,  290  and  294  have been correctly positioned in the knee portion  76  of the patient&#39;s leg  70 , the incision  114  is closed. 
     The general construction and mode of operation of the C-arm fluoroscope  360  ( FIG. 34 ) and control unit  362  is the same as is disclosed in U.S. Pat. Nos. 5,099,859; 5,772,594; 6,118,845 and/or 6,198,794. However, it is contemplated that other known image generating devices could be utilized in place of the fluoroscope if desired. For example, an image generating device similar to a magnetic resonance imaging unit (MRI) could be utilized. 
     In accordance with still another feature of the invention, a robot  370  ( FIG. 34 ) is provided to perform cutting and/or implant placement operations on the knee portion  76  in the leg  70  of a patient. The robot  370  includes a base  372 . A support column  374  is moveable vertically relative to the base  372 , in a manner indicated by arrows  376  in  FIG. 34 . In addition, the support column  374  is rotatable about coincident longitudinal central axes of the base  372  and support column in a manner indicated schematically by arrows  378  in  FIG. 32 . A main arm  382  is pivotally attached to an upper end portion of the support column  374 . Motors and controls  386  are connected with the main arm  382 . The main arm is pivotal relative to the support column  374  in the manner indicated by arrows  388  in  FIG. 34 . 
     A secondary arm  390  is pivotally mounted on an outer end portion of the main arm  382 . The secondary arm  390  is pivotal relative to the main arm  382  in the manner indicated by arrows  392 . A mounting section  396  is rotatable about a longitudinal central axis of the secondary arm  390  and has a mounting flange which is rotatable about an axis which extends perpendicular to the longitudinal central axis of the secondary arm  390 . 
     It is contemplated that a cutting tool, such as the saw  172 , may be mounted on the mounting section  396 . Controls for the robot  370  effect movement of the saw relative to the distal end portion  124  of the femur  126  to form the anterior cut surface  182  on the femur and to form a distal end cut on the femur. In addition, the robot  370  moves the saw to form chamfer cuts on the distal end portion  124  of the femur  126 . 
     The robot  370  may also be utilized to move the saw to make the cuts to form the proximal end portion  212  of the tibia  214 . Thus, the robot may be utilized to form the proximal tibial cut surface  246  ( FIG. 22 ). 
     By using the robot  370  to move the saw to form the cuts on the distal end portion  124  of the femur  126  and on the proximal end portion  212  of the tibia  214 , the need for instrumentation, such as the femoral alignment guide  134  and anterior resection guide  138  of  FIG. 11 , the distal resection guide  186  of  FIGS. 16 and 18 , and the tibial resection guide  218 , is eliminated. Controls for the robot  370  are connected with the C-arm fluoroscope  360  to enable the position of the saw relative to the femur and tibia to be viewed by the surgeon during an operation. 
     The robot  370  may have any one of many different constructions. Specifically, it is contemplated that the robot  370  may have the same construction as is disclosed in U.S. Pat. No. 5,154,717. Alternatively, the robot  370  could have the construction disclosed in U.S. patent application Ser. No. 09/789,621 filed Feb. 21, 2001 by Peter M. Bonutti. However, it should be understood that other known robots could be utilized if desired. For example, a robot similar to the known “Robo Doc”™ could be utilized. 
     It is contemplated that a computer navigation system may be used with the robot  370  to guide movement of a cutting tool, such as a saw or milling cutter, relative to the tibia and femur in the leg  70  of the patient. Two or more locating devices are connected with the distal end portion  124  of the femur  126 . In addition, two or more locating devices are connected to the proximal end portion of the tibia  214 . The locating devices cooperate with motors and computer controls  386  for the robot  370  to provide the robot with information as to the position of the mounting section  396  and cutting tool relative to the femur  126  and tibia  214 . 
     The locating devices may be of the reflective or energy emitting type or energy receiving type. For example, three reflectors may be pinned onto the distal end portion  124  of the femur  126 . Similarly, three reflectors may be pinned onto the proximal end portion  212  of the tibia  214 . Light transmitted from the robot  370  to the reflectors on the femur and tibia is reflected back to photo cells on the robot to enable the robot to determine the positions of the femur and tibia. Rather than using reflectors, energy emitting devices may be pinned onto the femur  126  and tibia  214 . The energy emitting devices may emit either light or radio waves. 
     The above-described image guided surgery system is merely intended to be representative of the type of system that can be used with the present invention. However, it should be understood that other known image guided surgery systems, both in conjunction and independent of robotic systems, could be utilized if desired. Examples of commercially available systems include systems the Z-KAT (Hollywood, Fla.) suites, the MEDIVISION system (Oberdorf, Switzerland), the STEALTH NAVIGATOR system (Louisville, Colo.), and the ORTHOPILOT System (Tuttlingen, Germany). 
     It should also be understood that the robot  370  could have any one of many different constructions. It is also contemplated that the robot  370  could interact with a surgeon and patient in many different ways. For example, the robot could have a plurality of articulate arms which are controlled by the surgeon. Images provided by the fluoroscope  360  would enable the surgeon to control the articulate arms. Locating devices connected with the femur and tibia are visible to the surgeon in images provided by the fluoroscope  360 . Computer controls which respond to the locating devices provide information to the surgeon about cutting tools and/or other instruments being moved by the articulate arms. The surgeon operated controls, the articulate arms, and the fluoroscope or other imaging device may cooperate in the manner disclosed in U.S. Pat. Nos. 6,063,095 and 6,102,850 if desired. 
     It is believed that it may be desired to use a hologram to provide a three-dimensional optical image of cuts to be made. The three-dimensional image would be projected onto the end portion  124  of the femur  126  and/or onto the end portion  212  of the tibia  214 . The three-dimensional image may be lines indicating where the femur  126  and/or tibia  214  are to be cut. 
     The three dimensional image would allow a surgeon  106  to visually monitor operation of the robot  370  during the making of cuts. If there was even a small discrepancy, the surgeon  106  could interrupt operation of the robot and take corrective action. It is believed that the projecting of a three-dimensional image onto surfaces to be cut will be particularly advantageous when a robotic system which has surgeon operated articulate arms is utilized. The projection of a hologram generated three-dimensional image would enable a surgeon to visually determine whether or not a robotic system, similar to the system disclosed in U.S. Pat. No. 6,063,095 or 6,102,850, is being operated properly. 
     Patellar Resection 
     In the foregoing description, the patella  120  was everted or flipped from its normal position to a position in which an inner side  122  of the patella faces outward ( FIG. 7 ). The patella  120  was then cut while it was in the everted position. A patellar implant was then mounted on the patella  120  in a known manner. The patella  120  was then returned to its normal position with the inner side of the patella facing inward toward the distal end portion  124  of the femur  126 . This is a well known manner of performing surgery on a patella to install a patellar implant. 
     In accordance with one of the features of the present invention and as discussed above, it is contemplated that the patella  120  will be cut and an implant positioned on the patella while the patella remains in a substantially normal position relative to the femur  126 . When the patella  120  is in its normal position relative to the femur  126  ( FIG. 35 ), an inner side  122  of the patella  120  is disposed adjacent to the distal end portion  124  of the femur  126 . The patella  120  is urged toward the trochlear groove  452  in the distal end portion  124  of the femur  126  by the patellar tendon  456  and the patellar ligament  458 . The patellar tendon  456  connects the patella  120  with the quadriceps femoris muscle. The patellar ligament  458  connects the patella  120  with the tibia  214 . The patellar tendon  456  and patellar ligament  458  may be referred to as fibrous connective tissue. 
     While the patella  120  is in the normal position illustrated in  FIG. 35 , a guide assembly  464  ( FIG. 36 ) is positioned relative to the patella. The guide assembly  464  includes a main section  466  ( FIG. 36 ) with a slot  468  having guide surfaces along which a blade  170  of a saw  172  is moved. The main section  466  of the guide assembly  464  is positioned relative to the patella  120  by a pair of parallel arms  474  and  476 . 
     The arm  474  extends through the medially offset incision  114  and under the superior aspect  480  of the in situ patella  120 . The arm  476  extends through the incision  114  and under the inferior aspect  482  of the in situ patella  120 . By positioning the arm  474  under the upper end portion  480  of the patella and the arm  476  under the lower end portion  482  of the patella  120 , the guide surfaces in the slot  468  are accurately aligned with the patella  120  while the patella is in its normal position relative to the femur  126  and tibia  214  ( FIG. 35 ). 
     While the in situ patella  120  is urged toward the distal end portion  124  of the femur  126  by the patellar tendon  456  and the patellar ligament  458  (fibrous connective tissue), the saw  170  or other cutting tool cuts along a plane  484  ( FIG. 35 ) to form a flat surface on the inside of the patella  120 . A relatively thin layer on which the inner side  122  of the patella is disposed, is then removed from the patella  120 . A patellar prosthesis or implant is then mounted on the cut surface on the inside of the patella while the patella remains in its normal position. A suitable cement can be utilized to connect the implant with the patella. In addition, one or more projections may be provided on the inside of the implant to interconnect the implant and the patella in a known manner. 
     The guide assembly  464  can include inflatable bladders as an adjunct or replacement for arms  474  and  476 . These bladders would elevate the patella  120  to obtain access to inner side  122 . In this regard, U.S. Pat. No. 5,163,949 and progeny, such as U.S. Pat. Nos. 6,358,266 B1, 6,277,136 B1, and 6,187,023 B1, discloses various embodiments of retractors and method of dissecting tissue. These embodiments include fluid operated retractors, mechanical retractors, and combinations thereof. The retractors and methods disclosed in this line of patents, which is incorporated herein by reference, can be used for patella procedures and/or visualization while the patella is maintained in a substantially non-everted, anatomic position. 
     If desired, the patella  120  may be repaired before making cuts on the femur  126  and tibia  214 . Thus, immediately after making the incision  114 , the patella  120  may be cut while it is disposed in its normal position. An implant may then be mounted on the patella  120 . The surgically repaired patella  120  may then be moved to the offset position of  FIG. 8 . The femoral and tibial cuts may then be made in the manner previously explained in association with  FIGS. 8-25  and the tibial and femoral implants  286 ,  290  and  294  mounted on the femur  126  and tibia  214  ( FIGS. 27-29 ) while the previously repaired patella is in the offset position. 
     Extramedullary Tibial Instrumentation 
     When a tibial resection guide  500  ( FIGS. 37 and 38 ) or the tibial resection guide  218  ( FIG. 21 ) is to be positioned relative to the proximal end portion  212  of the tibia  214 , an external tibial alignment guide  504  ( FIG. 37 ) may be used to position the tibial resection guide relative to the tibia  214 . The external tibial alignment guide  504  is disposed outside of the patient&#39;s leg  70  and extends along the lower portion  68  of the patient&#39;s leg. If desired, the patient&#39;s leg can be in the position illustrated in  FIGS. 2 ,  3 , and  25 . 
     The external tibial alignment guide  504  ( FIG. 37 ) includes a hollow distal shaft  508 . A proximal shaft  510  is telescopically received in the distal shaft  508 . When the proximal shaft  510  has been extended for a desired distance from the distal shaft  508 , a vertical adjustment knob  514  is tightened to hold the proximal shaft  510  against movement relative to the distal shaft  508 . 
     The foot or lower end portion of the hollow distal shaft  508  is connected with the mid-point between the palpable medial and lateral malleoli by a spring clamp  518 . The spring clamp  518  is aligned with the second metatarsal and grips the outside of the ankle portion  86  ( FIG. 25 ) of the patient&#39;s leg  70 . The proximal shaft  510  ( FIG. 37 ) of the external tibial alignment guide  504  is aligned with the medial third of the tibial tubercle. This results in the external tibial alignment guide  504  being positioned along the outside of the patient&#39;s leg with the longitudinal axis of the external tibial alignment guide  504  extending parallel to a longitudinal central axis of the tibia  214 . 
     A stylus  522  ( FIG. 38 ) is mounted on the tibial resection guide  500 . The stylus  522  engages the proximal end portion  212  of the tibia to position the tibial resection guide  500  relative to the tibia. The tibial resection guide  500  is connected to the proximal end portion  212  of the tibia by a single pin  524  ( FIG. 38 ) which extends through the tibial resection guide  500  into engagement with the proximal end portion  212  of the tibia  214 . The external tibial alignment guide  504  and the stylus  522  cooperate with the tibial resection guide  500  and pin  524  to hold the tibial resection guide against rotation. 
     Although the tibial resection guide  500  has been shown in  FIG. 38  as being connected directly to the proximal end portion  212  of the tibia  214 , the tibial resection guide could be connected with proximal end portion  212  of the tibia  214  in different manner. Thus, in  FIG. 38 , the posterior facing side of the tibial resection guide  500  is disposed in abutting engagement with the proximal end portion  212  of the tibia  214 . However, the posterior facing side of the tibial resection guide  500  could be positioned in engagement with skin which encloses the proximal end portion  212  of the tibia  214  in order to minimize the overall length of the incision  114 . This would result in the pin  524  extending through the tibial resection guide and through the skin and other tissue overlying the proximal end portion  212  of the tibia  214  into engagement with the proximal end portion of the tibia. The manner in which the tibial resection guide would be mounted on the tibia, would be similar to that disclosed in  FIG. 31  for the distal resection guide  186 . However, the tibial resection guide  500  is secured in place by a single pin  524 , by the external tibial alignment guide  504 , and, to some extent at least, the stylus  522 . 
     The tibial resection guide  500  is medially offset from the external tibial alignment guide  504 . This is because the incision  114  ( FIG. 6 ) is disposed adjacent to the medial edge portion of the patella  120 . If desired, the incision  114  could be disposed adjacent to the lateral side of the patella  120 . If this was done, the tibial resection guide  500  would be laterally offset from the external tibial alignment guide  504 . Regardless of which direction the tibial resection guide  500  is offset, a portion of the tibial resection guide may be disposed beneath body tissue to minimize the size of the incision  114 . 
     In accordance with a feature of the apparatus of  FIGS. 37 and 38 , the external tibial alignment guide  504  is maintained in position on the tibia  214  during cutting of the proximal end portion  212  of the tibia  214  in a manner similar to that illustrated in  FIG. 21 . Maintaining the tibial alignment guide  504  in place during cutting of the proximal end portion  212  of the tibia  214 , enables the tibial alignment guide to be utilized to position the tibial resection guide  500  relative to the tibia  214 . This enables the tibial resection guide  500  to be connected to the tibia  214  by only the single pin  524 . In the past, a plurality of pins have been utilized to connect the tibial resection guide  500  with the tibia  214  in a manner similar to the disclosures in U.S. Pat. Nos. 5,234,433 and 5,643,272. It should be understood that the tibial alignment guide  504  and a tibial resection guide, similar to the tibial resection guide  500 , may be utilized during performance of a partial knee replacement in the manner disclosed in the aforementioned U.S. Pat. No. 5,234,433. 
     Since, the external tibial alignment guide  504  is maintained in position during cutting of the tibia, the saw blade  170  or other cutting tool must be angled around the proximal shaft  510  of the external tibial alignment guide  504  as the proximal end portion  212  of the tibia  214  is cut. During movement of the saw blade  170  ( FIGS. 13 and 21 ) along the guide surface  530  ( FIG. 38 ), only an initial portion of the cut in the proximal end portion  212  of the tibia is made. This is because the proximal shaft  510  of the external tibial alignment guide  504  partially blocks the saw blade  170 . In addition, the tibial resection guide  500  is down sized. 
     Opposite ends  534  and  536  of the tibial resection guide  500  are space apart by a distance less than two thirds (⅔) of the distance between tips of lateral and medial epicondyles  236  and  238  ( FIG. 38 ) on the proximal end portion  212  of the tibia  214 . Therefore, after an initial portion of the cut across the proximal end portion  212  of the tibia  214  has been made while moving the saw blade  170  along the guide surface  530 , the tibial resection guide  500  and external tibial alignment guide  504  are disconnected from the tibia  214 . The tibial cut is then completed. 
     During completion of the tibial cut, the guide surface  530  on the resection guide  500  is not in position to guide the saw blade  170 . Therefore, cut surfaces fanned during the making of the initial portions of the tibial cut are utilized to guide the saw blade. When the tibial cut is to be completed the saw blade  170  is inserted into a slot or kerf formed in the distal end portion  212  of the tibia  214  by the saw blade  170  as it moved along the guide surface  530  and made the initial portion of the tibial cut. During completion of the tibial cut, the cut surfaces which were formed on the proximal end portion  212  of the tibia  214  during the initial portion of the tibial cut are used to guide movement of the saw blade. 
     The tibial resection guide  218  of  FIG. 21  has a guide surface  242  formed by a closed ended slot. The tibial resection guide  500  of  FIG. 38  has a guide surface  530  formed by an open ended slot. Thus, the tibial resection guide  500  includes a slot  540  which has an open end  542 . The open end  542  of the slot  540  facilitates movement of the saw blade  170  along the slot and angling of the saw blade relative to the slot to maximize the extent of the initial portion of the tibial cut. Thus, the extent of the tibial cut formed during movement of the saw blade along the guide surface  530  on the tibial resection guide  500  is maximized by forming the slot  540  with the open end  542  so that the saw blade can be angled at the open end  542  of the slot. 
     The tibial resection guide  500  may be used with a first cutting tool during making of the initial portion of the tibial cut. A second cutting tool may be used to complete the tibial cut. For example, a relatively small blade  170  of an oscillating saw  172  may be used to make the initial portion of the tibial cut. A relatively long blade of a reciprocating saw may be used to complete the tibial cut. If desired, a chisel and/or milling cutter could be used to make the initial portion and/or final portion of the tibial cut. 
     It is contemplated that it may be desired to set the tibial resection guide  500  ( FIG. 37 ) for any one of a plurality of different resection levels. Thus, the tibial resection guide  500  could be set to make a tibial cut at a distance of two millimeters from a location on the proximal end portion  212  of the tibia  214  which is engaged by the stylus  522 . Alternatively, the tibial resection guide  500  could be utilized to make a cut at a distance of eight millimeters from the location where the stylus  522  engages the proximal end portion  212  of the tibia  214 . Of course, the greater the distance at which the tibial cut is made from the location where the stylus  522  engages the proximal end portion  212  of the tibia  214 , the greater will be the thickness of a layer of bone removed from the distal end portion  212  of the tibia  214 . 
     To facilitate movement of the tibial resection guide  500  between various depths, the stylus  522  includes a drive assembly  548  ( FIG. 38 ). The drive assembly  548  is actuated by rotating a knob  550  on the stylus. Rotation of the knob  550  through a predetermined distance, that is, one complete revolution, will cause the drive assembly  548  to move the tibial resection guide  500  for a predetermined distance along the proximal shaft  510  of the external tibial alignment guide  504 . Thus, rotation of the knob  550  for one complete revolution in a clockwise direction, viewed from above, is effective to move the tibial resection guide  500  through a distance of two millimeters downwards along the proximal shaft  510  of the external tibial alignment guide. Of course, this would increase the depth of the tibial cut by a distance of two millimeters. Similarly, rotating the knob  550  through two complete revolutions is effective to actuate the drive assembly  548  to move the tibial resection guide  500  downward (as viewed in  FIG. 39 ) along the proximal shaft  510  of the external tibial alignment guide  504  through a distance of four millimeters. 
     The drive assembly  548  includes an externally threaded member which is connected with the knob  550 . An internally threaded member is connected with the tibial resection guide  500 . The internally threaded member engages the externally threaded member and is held against axial and rotational movement relative to the tibial resection guide  500 . 
     After the tibial resection guide  500  has been moved to a desired position relative to the proximal end portion  212  of the tibia  214 , a locking knob  556  is rotated to actuate a lock screw to hold the tibial resection guide  500  against movement along the proximal shaft  510  of the external tibial alignment guide  504 . The pin  524  is then inserted through the tibial resection guide  500  into the proximal end portion  212  of the tibia  214 . 
     Rather than moving the tibial resection guide  500  along the proximal shaft  510  of the external alignment guide  504  under the influence of force transmitted from the knob  550  through the drive assembly  548  to the tibial resection guide, the drive assembly could be connected with the knob  556 . For example, the knob  556  could be connected with a pinion gear of a rack and pinion drive arrangement. The rack portion of the drive arrangement could be mounted on the proximal shaft  510 . If this was done, rotation of the knob  556  would cause the rack and pinion gear set to move the tibial resection guide along the proximal shaft  510  through a distance which is a function of the extent of rotation of the knob  556 . The stylus  552  would be connected to the tibial resection guide  500  and would engage the proximal end of the tibia  214  to indicate when the tibial resection guide  500  had moved to a desired position relative to proximal end portion  212  of the tibia. 
     It is contemplated that the stylus  522  could be eliminated if desired. The tibial resection guide  500  could be positioned by sliding a thin member, such as a blade, beneath tissue overlying the proximal end portion  212  of the femur  214 . A reference surface on the tibial resection guide  500  would then be moved into engagement with the blade or other thin member. The reference surface may be disposed on the upper (as viewed in  FIG. 38 ) end of the tibial resection guide  500  or may be disposed in a slot in the tibial resection guide. The reference surface may also be utilized to guide movement of a saw or other cutting tool. 
     If desired a hook or sickle shaped locating member could be extended from the tibial resection guide  500  to position the tibial resection guide relative to the proximal end portion  212  of the tibia  214 . When the incision  114  and tibial resection guide  500  are medially offset relative to the tibia  214 , the locating member would extend along the medial side of the proximal end portion  212  of the tibia. This would enable the stylus  522  to be eliminated. 
     It is contemplated that retractors may be mounted on the proximal shaft  510  of the external tibial alignment guide  504 . The retractors engage opposite sides of the incision. The retractors are effective to expand the incision  114  and/or maintain the incision in a desired position relative to the proximal end portion  212  of the tibia  214 . 
     Cannula 
     In accordance with another feature of the invention, access to the interior of the knee portion  76  of the leg  70  may be obtained through a cannula  564  ( FIG. 39 ). The cannula  564  is inserted into the incision  114 . If desired, the patient&#39;s leg  70  can be in the position shown in  FIGS. 2 ,  3  and  25 . The upper portion of the patient&#39;s leg is supported by the leg support  80 . 
     The incision  114  is formed with a relatively short length in the manner previously described herein. The cannula  564  has an initial size, illustrated in  FIG. 39 , which stretches the viscoelastic material of tissues forming the knee portion  76  of the leg  70 . Therefore, initial insertion of the cannula  564  into the incision  114  is effective to expand the incision. 
     Compact cutting tools, similar to those utilized for arthroscopic, endoscopic, or fiber optic assisted surgery may be at least partially moved through a passage  566  ( FIG. 39 ) formed by an inner side  568  of the cannula  564 . The cutting tools may have a construction similar to the construction illustrated in U.S. Pat. No. 5,540,695 or 5,609,603. Alternatively, the cutting tools may have a construction similar to the construction disclosed in U.S. patent application Ser. No. 09/483,676 filed Jan. 14, 2000 by Peter M. Bonutti and having a disclosure which corresponds to U.S. Pat. No. 5,269,785. 
     The cannula  564  is advantageously expandable to further stretch the viscoelastic tissue of the knee portion  76 . Of course, expanding the cannula  564  increases the size of the passage  566  to enable a relatively large object to pass through the passage. Thus, the cannula  564  may be expanded to facilitate movement of the implants  286 ,  290  and  294  through the cannula. The leg  70  is in the position shown in  FIGS. 2 ,  3  and  24  during expansion of the cannula and movement of objects through the passage  566 . 
     It is contemplated that the expandable cannula  564  may have many different known constructions. The illustrated cannula  564  is formed of elastomeric material and has the same construction as is disclosed in U.S. patent application Ser. No. 08/470,142 filed Jun. 6, 1995 by Peter M. Bonutti, et al. and having a disclosure which corresponds to the disclosure in U.S. Pat. No. 5,961,499. It should be understood that the cannula  564  could have a different construction, for example, a construction similar to the constructions disclosed in U.S. Pat. No. 3,811,449 or 5,183,464. 
     The cannula  564  can be expanded in many different ways other than under the influence of force transmitted directly to the cannula from an object moving through the cannula. For example, the cannula may be expanded by force transmitted from an implant  286 ,  290  and/or  294  to the cannula. The cannula  564  may be expanded by inserting tubular members into the cannula. Alternatively, fluid pressure could be used to expand the cannula  564  in the manner disclosed in the aforementioned Bonutti, et al. patent application Ser. No. 08/470,142 filed Jun. 6, 1995. 
     Rather than being expanded by inserting the expandable cannula  564  into the incision  114 , the incision may be expanded by utilizing pneumatic retractors. The pneumatic retractors may have a construction similar to the construction disclosed in U.S. Pat. No. 5,163,949. By utilizing the expandable cannula  564  or the expandable pneumatic retractors, force can be applied against opposite sides of the incision  114  to stretch the viscoelastic material disposed adjacent to opposite sides of the incision. This will result in the relatively small incision  114  being expanded to accommodate relatively large surgical instruments and/or implants. 
     Although a single incision  114  is illustrated in  FIG. 39 , it is contemplated that a plurality of incisions could be provided. Thus, a small incision may be spaced from the incision  114  to enable a cutting tool to be moved into the knee portion  76  along a path which is spaced from and may be transverse to a path along which a cutting tool is moved through the incision  114 . A second cannula, which is smaller than the cannula  564 , may be utilized with the second incision. 
     Implant with Interconnectable Portions 
     In order to enable surgery on a knee portion  76  of a patient&#39;s leg  70  to be conducted through an incision  114  of relatively small size, the implant may advantageously be formed in two or more portions ( FIG. 40 ). The portions of the implant are sequentially moved through the incision  114  into engagement with the distal end portion  124  of the femur  126  and/or the proximal end portion  212  of the tibia  214 . It is believed that having the implant formed as two or more portions will facilitate movement of the implant through the cannula  564  ( FIG. 39 ). 
     As the portions of the implant are sequentially moved through the incision  114 , they are positioned in engagement with one or more of the bones, that is, the femur  126  and/or the tibia  214  in the leg  70  of a patient. After the plurality of portions of the implant have been moved through the incision  114  and positioned in engagement with the femur  126  and/or tibia  214 , the portions of the implant are interconnected to form a unitary implant. If desired, the portions of the implant are moved through the incision  114  and interconnected while the leg of the patient is in the position illustrated in  FIGS. 2 ,  3  and  25 . 
     It is contemplated that the portions of the implant may be interconnected, while they are disposed in the patient&#39;s body and in engagement with either the femur  126  and/or tibia  214 , in many different ways. For example, the portions of the implant may be bonded together to form a one piece implant. The portions of the implant may be bonded together by the application of energy in anyone of many different forms to a joint between portions of the implant. For example, ultrasonic energy could be applied to the implant. Alternatively, heat could be directly applied to the implant. If desired, a laser could be utilized to effect bonding of separate portions of the implant together. 
     It is also contemplated that the separate portions of the implant could be mechanically interconnected. This could be done with a fastener which extends between portions of the implant. Alternatively, a retainer member such as a rod or bar could extend between portions of the implant. Regardless of how the portions of the implant are interconnected, the portions of the implant are interconnected after they have been moved into the patient&#39;s body. 
     In the embodiment of the invention illustrated in  FIG. 40 , the femoral component  290  of an implant is formed as two separate portions  572  and  574 . The portion  572  of the implant  290  is moved through the incision  114  into engagement with the distal end portion  124  of the femur  126 . Thereafter, the portion  574  of the implant  290  is moved through the incision  114  into engagement with the distal end portion  124  of the femur  126 . After the two portions  572  and  574  of the femoral component  290  of the implant have been positioned in abutting engagement with the femur  126 , the two portions of the implant are interconnected at a joint  576  between the two portions of the implant. If desired, the portions  572  and  574  of the femoral component  290  of the implant may be moved through the cannula  564  of  FIG. 39 . 
     The specific implant  290  illustrated in  FIG. 40  has portions formed of a polymeric material which may be either a polymer or a co-polymer. The material of the two portions  572  and  574  of the implant  290  are heated at the joint  576  while the two portions of the implant are disposed in the patient&#39;s body in engagement with the femur  126 . As this occurs, the material forming the two portions  572  and  574  of the implant  290  is heated to a temperature within its transition temperature range and becomes tacky without changing its overall configuration. The two portions  572  and  574  of the implant  290  may be heated by the direct or indirect application of heat. The indirect application of heat may include applying ultrasonic energy to the implant. 
     The heated material of the two portions  572  and  574  of the implant  290  are then pressed together at the joint  576  to form a bond between the two portions of the implant. As this occurs, there is a fusing of the material of the portion  572  of the implant  290  with the material  574  of the implant. This fusing together of the two portions  572  and  574  occur in the patient&#39;s body and results in the formation of a one-piece unitary implant  290 . 
     Rather than being formed of a polymeric material, it is contemplated that the two portions  572  and  574  of the implant could be formed of metal and have a polymeric layer on a side of the metal toward the femur  126 . This would result in the layer of polymeric material being disposed in engagement with the distal end portion  124  of the femur  126  and the metal forming the femoral component  290  facing toward the tibia  214  for engagement with the tibial bearing insert  294  ( FIG. 32 ). With such a construction, the application of energy to the two portions  572  and  574  of the implant would result in a heating of the layer of polymeric material on the inside of the layer of metal. The heated polymeric materials on the two portions  572  and  574  bond together at the joint  576  in a manner previously described. 
     When the two portions  572  and  574  of the femoral implant  290  are to be interconnected by fusing together sections of polymeric material which form the portions  572  and  574  of the implant or sections of polymeric material which are disposed on layers of metal forming part of the portions  572  and  574  of the implant  290  to be interconnected, it is contemplated that they may be interconnected in many different ways. One way in which polymeric material on the portions  572  and  574  of the femoral implant  290  may be interconnected is the same as is disclosed in U.S. patent application Ser. No. 09/737,380 filed Dec. 15, 2000 by Peter M. Bonutti, et al. This patent application contains a disclosure which corresponds to the disclosure in U.S. Pat. No. 6,059,817. 
     The two portions  572  and  574  of the implant  290  ( FIG. 40 ) may be formed of only metal. If this is done, the two portions  572  and  574  of the implant may be mechanically interconnected. For example, a screw could extend from the portion  574  of the implant  270  to the portion  572  of the implant while the two implants are in engagement with the distal end portion  124  of the femur  126 . Alternatively, a snap type joint  576  could be provided between the portions  572  and  574  of the implant. Although the two portions  572  and  574  of the implant  290  are positioned in engagement with the femur  126  and interconnected while the leg  70  of the patient is in the position illustrated in  FIGS. 2 ,  3  and  25 , the two portions of the implant could be positioned in engagement with the femur  126  while the leg  70  is straight (extended). 
     The implant  290  is connected with the femur  126 . However, it is contemplated that a tibial implant could be formed as a plurality of separate portions which are interconnected when they are in the knee portion  76  of the patient&#39;s leg  70 . It should be understood that the implant  290  could be formed of more than two portions. For example the implant could be formed with four separate portions which are interconnected in the patient&#39;s body. Although the implant  290  is to be used in a knee portion of a patient&#39;s body, it is contemplated that implants used at other portions of a patient&#39;s body could be interconnected in the patient&#39;s body. 
     In the embodiment of the invention illustrated in  FIG. 40 , the separate portions  572  and  574  of the implant  290  are positioned in engagement with the same bone, that is, femur  126  and interconnected. However, it is contemplated that one position of an implant could be positioned in engagement with a first bone and another portion of the implant positioned in engagement with a second bone. However, the two portions of the implant would be interconnected in the patient&#39;s body. The two portions of the implant may be interconnected after they have been positioned in engagement with bones in the patient&#39;s body. Alternatively, the two portions of the implant could be interconnected in the patient&#39;s body, before one or both portions of the implant have been positioned in engagement with a bone. 
     For example, a first component of an implant may be connected with a femur  126  in a patient&#39;s body. A second component may be connected with a tibia  214  in the patient&#39;s body. The two components are interconnected, in the patient&#39;s body, after they have been connected with the femur and tibia. 
     Transducer for Ligament Balancing 
     After the femoral component  290  and tibial components  286  and  294  of the implant had been positioned in the knee portion  76  of the patient&#39;s leg  70 , the ligaments are balanced in flexion, extension, and rotation in the manner previously described. It should be understood that even though the implants have not been shown in  FIGS. 41 and 42 , ligament balancing may be undertaken before and/or after the implants been positioned in engagement with the femur  126  and tibia  214 . However, it is contemplated that ligament balancing could be undertaken during surgical procedures which do not require cutting of the femur  126  and tibia  214  and/or implants. 
     In accordance with one of the features of the invention, during ligament balancing, tension forces in fibrous connective tissue such as collateral ligaments  590  and  592  ( FIGS. 41 and 42 ) are compared. If the forces in one of the ligaments  590  or  592  are excessive, the ligament in which the excessive force is present may be released. Similarly, if one of the ligaments is too loose, the ligament may be tightened. 
     In accordance with another one of the features of the invention, transducers are positioned between one or more bones in the knee portion  76  of the leg  70  of the patient. The transducers enable tension forces in ligaments  590  and  592  to be compared. The transducers may be used to determine the magnitude of the tension forces in the ligaments  590  and  592 . 
     Thus, a first or lateral transducer  596  ( FIGS. 41 and 42 ) is positioned between a lateral side of the distal end portion  124  of the femur  126  and a lateral side of the proximal end portion  212  of the tibia  214 . Similarly, a second or medial transducer  598  is positioned between a medial side of the distal end portion  124  of the femur  126  and a medial side of the proximal end portion of the tibia  214 . The transducers  596  and  598  are connected with a computer  600  ( FIG. 41 ) or other processor. 
     The computer  600  ( FIG. 41 ) has a display area  601  at which the output from the lateral transducer  596  is displayed. Similarly, the computer  600  has a display area  602  at which the output from the medial transducer  598  is displayed. By comparing the outputs at the display areas  601  and  602 , a surgeon can determine the relationship between the tension in the ligament  590  and the tension in the ligament  592 . In addition, the surgeon can determine the magnitude of the tension in the ligaments  590  and  592 . 
     It is contemplated that the leg  70  of the patient will be moved between the flexed condition of  FIGS. 2 ,  3 ,  25  and  41  and an extended position or straight condition ( FIGS. 4 and 42 ), while the output from the transducers  596  and  598  is viewed at the display areas  601  and  602  of the computer  600 . This will provide the surgeon with a clear indication of the manner in which tension forces in the ligaments  590  and  592  varies during bending of the knee portion  76  of the leg  70  of a patient. If an image generating device, similar to the C-arm fluoroscope  360  of  FIG. 34 , is used in association with the transducers  596  and  598 , the surgeon can see how components of the knee joint are interacting as the tension in the ligaments varies. 
     In addition to checking the tension in the ligaments  590  and  592  during movement of the leg  70  of the patient between flexed and extended conditions, it is contemplated that the tension in the ligaments  590  and  592  will be compared during the application of rotational forces to the lower portion  68  of the knee of the patient. Thus, forces tending to rotate the lower portion  68  of the leg of the patient in the direction of the arrow  258  in  FIG. 25  are applied to the lower portion  68  of the leg  70 . As these rotational forces are applied, the outputs from the transducers  596  and  598  ( FIG. 41 ) are displayed for review by a surgeon to determine whether or not the ligaments  590  and  592  are rotationally balanced. The transducers  596  and  598  may be utilized to provide outputs corresponding to forces resulting from a combination of flexion/extension movement and rotational movement of the lower portion  68  of the patient&#39;s leg  70 . It should be understood that the transducers  596  and  598  may be utilized throughout the entire ligament balancing process previously described herein in order to enable a surgeon to compare tension forces in the ligaments  590  and  592  throughout the ligament balancing process. 
     Although the transducers  596  and  598  have been illustrated schematically in  FIGS. 41 and 42  as being associated with the end portions of the femur  126  and tibia  214 , it should be understood that the transducers  596  and  598  could be associated with other joints if desired. For example, the transducers  596  and  598  could be positioned between vertebrae in a patient&#39;s spine. If this was done, the patient&#39;s spine could be bent in either anterior or lateral flexion and extension. The output at the display areas  601  and  602  would indicate the manner in which forces transmitted between the vertebrae vary during bending of the spine. 
     It is contemplated that the transducers  596  and  598  could have many different constructions. However, in the illustrated embodiment of the invention, the transducers  596  and  598  are pneumatic transducers. Thus, the lateral transducer  596  ( FIG. 42 ) includes a container or bladder having a chamber which is filled with fluid. It is contemplated that the chamber could be filled with either a gas or a liquid. In the embodiment of the invention illustrated in  FIGS. 41 and 42 , the transducers  596  and  598  have the same construction and are of pneumatic type. Therefore, the chamber is filled with air. However, the chamber could be filled with a liquid, for example, saline solution, if desired. 
     The transducers  596  and  598  are disposed between the femur  126  and the tibia  214 . Although it should be understood that the femoral implant  290  and tibial tray  286  and bearing  294  have not been illustrated in  FIGS. 41 and 42 , the implants may or may not be present when the transducers are positioned between the femur  126  and tibia  214 . Depending upon the location of the transducers  596  and  598  they may or may not be disposed in engagement with a portion of either the femoral or tibial implant. With a partial knee replacement, one of the transducers  596  or  598 , is disposed between femoral and tibial implants. The other transducer is disposed between surfaces on the femur  126  and the tibia  214 . 
     A conductor  604  is provided to transmit an output signal from the lateral transducer  596  to the computer display  601  ( FIG. 42 ). The conductor  604  could be constructed so as to conduct either fluid pressure from the transducer  596  to the computer  600  or to conduct an electrical signal from a fluid pressure transducer exposed to the fluid pressure in the transducer  596 . The medial transducer  598  is connected with the display  602  by a conductor  606 . 
     It is contemplated that the transducers  596  and  598  could have many different constructions including any one of the constructions disclosed in U.S. Pat. No. 5,667,520 or in U.S. patent application Ser. No. 09/483,676 filed Jan. 14, 2000 by Peter M. Bonutti and having a disclosure corresponding to the disclosure in U.S. Pat. No. 5,269,785. The transducers  596  and  598  may be formed of a material which is biodegradable or a material which is non-biodegradable. 
     Although the illustrated transducers  596  and  598  ( FIGS. 41 and 42 ) are of the pneumatic type, it is contemplated that a different type of transducer could be utilized if desired. For example, the transducers  596  and  598  could be solid state devices, such as piezoelectric load cells. Alternatively, the transducers could include deformable members to which strain gauges are attached. 
     It should be understood that the transducers  596  and  598  could be used to measure and/or compare tension in the ligaments  590  and  592  immediately after making the incision  114 . In addition or alternatively, the transducers  596  and  598  could be used to measure and/or compare tension in the ligaments  590  and  592  during trials with provisional components. Of course, the transducers  596  and  598  can be used to measure and/or compare tension in the ligaments after the implants  286 ,  290  and  294  have been mounted in the knee portion  76 . 
     In the embodiment of this invention illustrated in  FIGS. 41 and 42 , the transducers  596  and  598  are disposed between end portions of the femur  216  and tibia  214 . Therefore, the transducers  596  and  598  only indirectly respond to variations in tension in the collateral ligaments  590  and  592 . It is contemplated that the transducers  596  and  598  could be positioned so as to directly respond to variations in the tension in the collateral ligaments  590  and  592 . 
     For example, the transducer  596  could be positioned between the ligament  590  and lateral sides of the femur  126  and/or tibia  214 . Similarly, the transducer  598  could be positioned between the ligament  592  and medial sides of the femur  126  and/or tibia  214 . 
     It is contemplated that transducers, similar to the transducers  596  and  598 , could be utilized to determine variations in tension in ligaments and/or tendons other than the ligaments  590  and  592 . For example, transducers could be utilized to determine the tension in the patellar tendon  456  ( FIG. 42 ) and/or the patellar ligament  458 . If desired, transducers, similar to the transducers  596  and  598 , could be positioned so as to respond to variations in tension in the posterior cruciate ligament  250  and/or the anterior cruciate ligament. It is contemplated that a plurality of transducers, similar to the transducers  596  and  598 , may be positioned so as to respond to variations in tension in various combinations of ligaments and/or tendons. 
     In addition to providing outputs which are a function of variations in tension in ligaments and/or tendons, the transducers  596  and  598  may be utilized to apply force against the femur  126  and tibia  214 . When this is to be done, fluid under pressure is conducted to either or both of the transducers  596  and/or  598 . An increase in fluid pressure conducted to the transducers  596  and  598  is effective to expand containers or bladders in the transducers. 
     The fluid pressure force applied against the transducers  596  and/or  598  is transmitted to the femur  126  and tibia  214 . This force may be used to stretch the collateral ligaments  590  and  592  and/or other body tissue. If it is desired to stretch one of the ligaments  590  or  592  to a greater extent the other ligament, the fluid pressure transmitted to one of the transducers  596  or  598  would be greater than the fluid pressure transmitted to the other transducer. The force transmitted to the femur  126  and tibia  214  is indicated at the displays  61  and  601 . 
     It is contemplated that the transducers  596  and  598  will be removed before the limited incision  114  is closed. However, if it is desired, the transducers  596  and  598  may be left in place and utilized after the incision  114  is closed. When this is to be done, the transducers  596  and  598  may advantageously be formed of biodegradable material. By leaving the transducers  596  and  598  in place after the incision  114  is closed, the tension in the ligaments  590  and  592  may be compared during therapy. If desired, one or both ligaments  596  and/or  598  could be conducting fluid pressure to one or both transducers  596  and/or  598  during therapy. 
     Inlaid Implant—Femur 
     In the embodiment of the invention illustrated in  FIGS. 8-28 , articular surfaces on the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214  are cut away using a saw or other cutting tool. This results in areas on the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214 , where articular surfaces were previously disposed, being cut to have a flat planar configuration. Thus, an anterior skim cut, a distal end cut, and chamfer cuts are made on the distal end portion  124  of the femur  126  while a proximal end cut is made on the proximal end portion  212  of the tibia  214 . After the cuts have been made, the femoral implant extends across or encloses the cuts on the distal end portion  124  of the femur  126  and the tibial implant extends across the cut on the tibial end portion  212  of the tibia  214 . 
     It is contemplated that rather than enclosing the end portions of the femur and tibia with implants, the implants could be inlaid into the end portion of the femur and/or tibia. When an implant is to be inlaid into the distal end portion  124  of the femur  126  ( FIG. 43 ), a recess  610  is formed in the distal end portion  124  of the femur  126 . To form the recess  610 , a cutting tool, such as a milling cutter  614  ( FIG. 44 ), is utilized to cut away a defective portion of an articular surface on the distal end portion  124  of the femur  126 . The milling cutter  614  is rotated about its longitudinal central axis and has cutting edges disposed in a cylindrical array about the periphery of the milling cutter. The extent of the defective portion of the articular surface determines the extent to which the milling cutter  614  cuts away the articular surface. 
     A guide  620  ( FIG. 44 ) is provided for the milling cutter or other cutting tool. The guide  620  is effective to limit the extent of axial movement of the milling cutter  614  into the distal end portion  124  of the femur  126  to thereby limit the depth of the recess  610 . The guide  620  limits side wise, that is, radial movement of the milling cutter  614  to an area corresponding to the desired configuration of the recess  610 . This results in the recess  610  being fanned with a uniform depth throughout the extent of the recess and with a desired configuration. The construction of the guide  620  in the manner in which it cooperates with the milling cutter  614  may be similar to that disclosed in U.S. Pat. Nos. 5,344,423; 5,769,855; and/or 5,860,981. 
     Once the recess  610  has been formed using the milling cutter  614  in the manner illustrated schematically in  FIG. 44 , an implant  626  ( FIGS. 43 and 45 ) is positioned in the recess. The implant  626  fills the recess  610  and has an outer surface  628  ( FIG. 45 ) which forms a continuation of the naturally occurring articular surface  616  formed by the distal end portion  124  of the femur  126 . The outer surface  628  of the implant  626  replaces defective articular surface area removed by the milling cutter  614  from the distal end portion  124  of the femur  126 . 
     The outer surface  628  on the implant  626  cooperates with an articular surface on a tibia  214  in the same general manner as the original articular surface area removed by the milling cutter  614 . Of course, the outer surface  628  of the implant  626  is free of defects that made it necessary to replace the corresponding area on the articular surface  616  of the distal end portion  124  of the femur  126 . The outer surface  628  of the implant  626  may engage an articular surface formed by the boney material of the tibia  214 . Alternatively, the outer surface  628  of the implant  626  may engage the surface of an implant disposed on the tibia  214 . 
     During recovery of the patient, the naturally occurring surface  616  on the femur  126  and the implant  626  may both be load bearing. By having the implant  626  surrounded by load bearing natural bone, the implant is held in place on the distal end portion  124  of the femur  26 . In addition, the magnitude of the load which must be transmitted through the implant  626  is minimized. 
     The implant  626  could have any desired construction. Thus, the implant could be formed of a polymeric material or it could be formed of a metallic material. However, in accordance with one of the features of the invention, the implant  626  is formed of a material which promotes biological resurfacing and the growth of bone from the distal end portion  124  of the femur  126  into the implant to fill the recess  610  with new bone growth. The implant  626  may also be at least partially formed of material which promotes the growth of cartilage or other tissue over the implant. 
     The implant  626  may be formed with a non-living three dimensional scaffold or framework structure on which bone growth promoting materials, such as bone morphogenetic proteins, are disposed. The three dimensional framework or platform on which the bone growth promoting materials are disposed may be formed of either a biodegradable or a non-biodegradable material. When the scaffold or framework structure is formed of a non-biodegradable material, the bone from the distal end portion  124  will grow through the scaffold so that the scaffold becomes embedded in new bone growth. The scaffold may be formed of a porous metal or ceramic material. When the scaffold is formed of a bio-degradable material, the scaffold will eventually degrade and be absorbed by body tissue. 
     The scaffold may be formed of a mesh or a felt-like material, or a porous material similar to coral. The scaffold forms a growth supporting matrix to support cellular migration from the boney material of the distal end portion  124  of the femur  126  into the implant  626 . If the scaffold or platform is made of a bio-degradable material, then the scaffold or platform degrades and disappears after a period of time. It is contemplated that the scaffold could be formed of a bio-degradable material such as polyglycolic acid or polylactic acid. If desired, the scaffold or framework could be formed of fibrous connective materials such as portions of ligaments, tendons and/or bones obtained from human and/or animal sources. The scaffold could be formed of collagen. The scaffold may be formed of submucosal tissue. 
     The scaffold holds bone growth inducing materials and may include bone fragments to which tri-calcium phosphate, an antibiotic, hydroxyapatiate, allografts, autografts, and/or any other polymeric has been added. It is believed that it will be particularly advantageous to provide a bone growth morphogenetics protein in the implant  626  to promote the growth of bone into the implant. The scaffold may hold cultured and/or noncultured cells which promote biological resurfacing. 
     The matrix or scaffold for the implant  626  may contain tissue inductive factors and/or cells. The cells may be mesenchymal cells which are introduced into the scaffold in the operating room. Thus, the matrix or scaffold may be either biodegradable or non-biodegradable and may be constructed at a location remote from an operation. After the scaffold has been transported to the operating room the mesenchymal cells may be introduced into the scaffold. 
     It is contemplated that the matrix or scaffold for the implant  626  may contain stem cells and/or fetal cells. The stem cells and/or fetal cells may be introduced into either a biodegradable or non-biodegradable matrix or scaffold in the operating room. It is contemplated that tissue inductive factors may be provided in the matrix or scaffold along with any desired type of precursor cells. 
     The matrix or scaffold for the implant  626  may contain osteoinductive materials. The implant  626  may contain osteoblasts or osteoclast cells or their precursors. The implant  626  may also contain platelet matrix centrifuged from blood in a manner similar to that described in U.S. patent application Ser. No. 09/483,676, filed Jan. 14, 2000 by Peter M. Bonutti. 
     The matrix or scaffold for the implant  626  may be formed of allograft bone or collagen. Cartilage may be used to form the scaffold or matrix. The scaffold or matrix for the implant  626  may have a layered construction with the layers being formed of different materials. Each of the layers of the scaffold or matrix forming the implant  626  may be impregnated with a different material. For example, precursor cells may be provided in one layer and bone morphogenetic protein may be provided in another layer. 
     It is contemplated that submucosal tissue may be used to form the scaffold for one or more of the layers of the implant  626 . The submucosal tissue may be prepared in a manner similar to the manner disclosed in U.S. Pat. No. 5,755,791. The various layers of the implant  626  may be assembled in the operating room. 
     The implant  626  may be formed of multiple tissue fragments. Thus, a tissue press, similar to the tissue presses disclosed in U.S. patent application Ser. No. 09/602,743 filed Jun. 23, 2000, by Peter M. Bonutti and having a disclosure which corresponds to the disclosure in U.S. Pat. No. 5,662,710 may be utilized to shape the implant to a desired configuration. 
     The implant  626  may be formed to have any one of a plurality of different sizes and configurations. The implant may be shaped to the desired configuration at a location remote from an operating room and transported to the operating room. Alternatively, the implant  626  could be cut to the desired shape in the operating room. 
     By providing a substantial number of implants of different sizes in the operating room and/or by cutting an implant to obtain a desired configuration, it is possible for a surgeon to make a recess  610  to a shape which corresponds to a defective area on a portion of the femur  126 . An implant  626  having the configuration of the particular recess can then be provided. This enables the surgeon to remove a relatively small defective area of the bone forming the articular surface on the femur  126  and to minimize the size of the implant  626 . 
     It is believed that it will be desired to provide a series of implants of different sizes ranging from a relatively small size to a relatively large size. In addition, it is believed that it will be desired to provide a plurality of guides  620 . The guides  620  will have surfaces to guide movement of the milling cutter  614  or other cutting tool to form a recess  610  of a size corresponding to any one of the sizes of the implants in the series of implants. Thus, the plurality of guides  620  would be provided with each guide having guide surfaces corresponding to the configuration of an implant of a different size. 
     The scaffold or base of the implant  626  may be formed of a porous bio-degradable material. The porous bio-degradable material provides a matrix for demineralized bone, collagen, bone morphogenetic protein, growth factors, and autogenous bone marrow. In addition, progenitor cells, stem cells and/or fetal cells may be disposed on the scaffold. Some non-tissue-derived components may include coralline-based HA (ProOsteon), antibiotics, calcium sulfate, calcium and phosphorus oxide rich amorphous glass, anti-inflammatories, and bovine fibrillar collagen. The resulting material will have osteoinductive and osteoconductive qualities. Cortical cancellous bone chips which are freeze dried may be provided in the implant  626 . In addition, demineralized bone matrix may be provided in the implant  626 . 
     The implant  626  may be secured in the recess  610  with a suitable adhesive. There are many different known adhesives which may be used. Fibrin can be used as an adhesive, either in a natural state or after being compressed, to hold material together and to hold the implant  626  in the recess  610 . 
     It is contemplated that the patient&#39;s leg  70  may be in the position illustrated in  FIGS. 2 ,  3  and  25  during forming of the recess  610  and positioning of the implant  626  in the recess. The upper portion  72  of the patient&#39;s leg  70  may be supported above the support surface  64  by the leg support  80 . The limited incision  114  ( FIG. 6 ) may be formed in the knee portion  76  of the patient&#39;s leg. The patella  120  may be in the offset position of  FIG. 8  during forming of the recess  610 . 
     The drapery system  100  of  FIGS. 4 and 5  may advantageously be utilized to provide a sterile field. Although it may be desired to use a milling cutter as the cutting tool  614  ( FIG. 44 ), other known cutting tools could be used if desired. For example, a laser or ultrasonic cutting tool could be used to form the recess  610 . 
     Although it is believed that it will be preferred to have the patient&#39;s leg  70  in the position illustrated in  FIGS. 2 ,  3  and  25 , to support the patient&#39;s leg  70  with the leg support  80 , to offset the patella  120 , and to use the drapery system  100 , the implant  626  may be positioned in a patient&#39;s leg  70  without using any one or any combination of these features. Thus, the implant  626  could be positioned in a patient&#39;s leg  70  with the leg in the position shown in  FIG. 1  with any known drapery system. The patella may be everted ( FIG. 7 ) rather than offset. 
     The foregoing description of the implant  626  has assumed that the implant is to be positioned in the femur  126  in a leg of a patient. However, the implant  626  could be positioned in any desired bone in a patient&#39;s body. The implant  626  could be positioned at a location remote from an articular surface of a bone. The implant  626  may be positioned on a bone in ways other than positioning the implant in a recess similar to the recess  610 . 
     Inlaid Implant—Tibia 
     The implant  626  is illustrated in  FIG. 43  in association with a femur  126  in a patient&#39;s body. It is contemplated that a similar implant  640  ( FIG. 46 ) may be provided in the proximal end portion  212  of the tibia  214  in a leg  70  of the patient. The implant  640  is disposed in a recess  642 . The recess  642  may have any desired configuration. It is contemplated that the configuration of the recess  642  would be a function of the configuration of defective portions of the bone in the proximal end portion  212  of the tibia  214 . 
     The recess  642  is surrounded by an articular surface  644  of naturally occurring bone. Thus, the articular surface  644  is not defective and extends around the recess  642 . It should be understood that the extent of the articular surface  644  around the recess  642  could be substantially greater than is illustrated in  FIG. 46  relative to the size of the implant  640 . This is because the implant  640  is sized and has a configuration which is a function of the size and configuration of an area which was previously defective bone on the proximal end portion  212  of the tibia  214 . The articular surface  644  is load bearing and functions to transmit forces between the tibia  214  and the femur  126  in the leg  70  of the patient. 
     The recess  642  is formed with the milling cutter  614  ( FIG. 47 ). A guide  620  is provided to control the depth to which the milling cutter  614  removes bone from the proximal end portion  212  of the tibia  214  in the manner previously explained in conjunction with femur  126  ( FIGS. 43-45 ). The guide  620  and milling cutter  614  are utilized to form the recess  642  in a manner which is similar to that disclosed in U.S. Pat. No. 5,908,424. Rather than being formed by the use of a milling cutter  614  and guide  620 , it is contemplated that the recess  642  in the proximal end portion  212  of the tibia  214  and/or the recess  610  in the distal end portion  124  of the femur  126  could be formed by a robot having a construction similar to the construction of the robot  370  of  FIG. 33 . 
     The implant  640  ( FIGS. 46 and 48 ) may be formed of metal or a hard polymeric material. Alternatively, the implant  626  may be of a layered construction with a layer of metal backed by polymeric material. The surface of the implant forms a portion of the overall articular surface on the proximal end portion  212  of the tibia  214 . 
     Of course, the articular surface area on the proximal end portion  212  of the tibia  214  cooperates with articular surface areas on the distal end portion  124  of the femur  126  ( FIG. 43 ). It is contemplated that the implant  626  in the femur  126  and the implant  640  in the tibia  214  ( FIG. 46 ) could be disposed in engagement with each other. Alternatively, the implant  626  in the distal end portion  124  of the femur  126  ( FIG. 43 ) could be engaged by a naturally occurring articular surface on the proximal end portion  212  of the tibia  214  ( FIG. 46 ). Similarly, the implant  640  in the proximal end portion  212  of the tibia  214  may engage a naturally occurring articular surface area on the distal end portion  124  of the femur  126 . 
     It is contemplated that it may be preferred that the implant  640  contain bone growth promoting materials and/or materials which promote biological resurfacing. These bone growth promoting materials would promote growth of bone from the proximal end portion  212  of the tibia  214  into the recess  642 . This would result in the recess  642  being filled with new bone growth. The biological resurfacing materials would promote the growth of naturally occurring tissues on the implant  640 . 
     The implant  640  may include a three dimensional scaffold or framework structure formed of either a biodegradable material or a non-biodegradable material. Osteoinductive and/or osteoconductive materials may be disposed on this framework or platform. The scaffold may be formed of cortical bone, cartilage submucosal tissue, or other materials. 
     The matrix or scaffold for the implant  640  has interstitial spaces which contain material which promotes the growth of bone from the proximal end portion  212  of the tibia  214  into the matrix or scaffold. The bone growth materials may include bone morphogenic protein, factors that stimulate migration of cells, anti-inflammatories and/or immuno suppressants. Collagen, fibrin, osteoinductive materials, progenitor cells, and/or tissue inductive factors may be disposed on the platform. The implant  640  may contain cortical cancellous bone chips or demineralized bone matrix. It may be preferred to form the outer surface of the implant  640  of materials which promote biological resurfacing. 
     When the implant  640  is formed with a biodegradable three dimensional scaffold or matrix, it is contemplated that there will be cellular migration and growth of bone from the proximal end portion  212  of the tibia  214  into the scaffold or matrix. The scaffold or matrix will then degrade and disappear as material of the scaffold or platform hydrolyzes. However, if the matrix or scaffold is made of a non-biodegradable material, it is contemplated that the scaffold will become embedded in the bone growth from the proximal end portion  212  of the tibia  214  into the recess  614 . The scaffold, whether biodegradable or non-biodegradable, may be impregnated with mesenchymal cells. 
     The implant  640  on the tibia has the same construction as the implant  626  on the femur. However, the implant  640  on the tibia could have a construction which is different than the construction of the implant  626  on the femur. 
     It is contemplated that the patient&#39;s leg will be in the position illustrated in  FIGS. 2 ,  3  and  25  during forming of the recess  642  and positioning of the implant  640  in the recess. The upper portion  72  of the patient&#39;s leg  70  will be supported above the support surface  64  by the leg support  80 . The limited incision  114  ( FIG. 6 ) will be formed in the knee portion  76  of the patient&#39;s leg. The patella  120  will be in the offset position of  FIG. 8  during forming of the recess  642 . The drapery system of  FIGS. 4 and 5  may advantageously be utilized to provide a sterile field. Although it may be desired to use a milling cutter as the cutting tool, other known cutting tools could be used if desired. 
     Layered Implant 
     A multi layered inlaid implant  670  for use in biological resurfacing is schematically illustrated in  FIG. 49 . The implant  670  is disposed in a recess  672  formed in a bone  674 . The recess  672  is formed in the same manner as is illustrated in  FIGS. 44 and 47  for forming the recess  610  and the recess  642 . The recess  672  may be disposed in a defective portion of an articular surface on the distal end portion  124  of a femur  126 , as illustrated in  FIG. 43 , or may be located at a defective portion of an articular surface on the proximal end portion  212  of a tibia  214  as illustrated in  FIG. 46 . However, it is contemplated that the implant  670  may be disposed in the bone  674  at many different locations. At least some of these locations would be spaced from an articular surface on the bone. The bone may be located in many different portions of a patient&#39;s body, for example, a shoulder, spine, arm, hand, hip or foot. 
     The implant  670  is formed by a plurality of layers. The specific implant  670  illustrated in  FIG. 49  has a base layer  678  and an outer layer  680 . It should be understood that more than two layers could be provided if desired. For example, an intermediate layer could be disposed between the base layer  678  and outer layer  680  if desired. Each of the layers  678  and  680  of the implant  670  could be formed with its own separate platform or scaffold made of biodegradable materials. Alternatively, a single biodegradable scaffold or matrix could extend between the two layers  678  and  680 . 
     The inner or base layer  678  is disposed in engagement with the bone  674 . The inner layer  678  may be formed of bone growth promoting materials which promote migration of bone cells from the bone  674  to the base layer  678 . New bone growth into the base layer  678  will interconnect the base layer and the bone  674 . The base layer  678  may contain cortical cancellous bone power or chips and/or demineralized bone matrix, bone morphogenic protein, anti-inflammatories and/or immuno suppressants may be disposed in the base layer  678 . An antibiotic, hydroxyapatiate, tricalcium phosphate and/or polymers and copolymers may also be included in the base layer  678 . 
     The outer layer  680  may be formed of cartilage. Embryonal cells, fetal cells, and/or stem cells may be provided in the outer layer  680 . The outer layer  680  may be formed of submucosal tissue. The outer layer  680  promotes biological resurfacing of a portion of the bone  674  where the implant  670  is disposed. 
     It is contemplated that the recess  672  may be formed in the bone  674  at a location where there is a defect in an articular surface on the bone. However, it is also contemplated that the recess  672  in a position in a portion of the bone  674  where there is no articular surface. 
     It is contemplated that the patient&#39;s leg will be in the position illustrated in  FIGS. 2 ,  3  and  25  during forming of the recess  672  and positioning of the implant  670  in the recess. The upper portion  72  of the patient&#39;s leg  70  will be supported above the support surface  64  by the leg support  80 . The limited incision  114  ( FIG. 6 ) will be formed in the knee portion  76  of the patient&#39;s leg. The patella  120  will be in the offset position of  FIG. 8  during forming of the recess  672 . The drapery system of  FIGS. 4 and 5  may advantageously be utilized to provide a sterile field. Although it may be desired to use a milling cutter as the cutting tool, other known cutting tools could be used if desired. 
     Implant 
     An improved implant  690  is illustrated in  FIG. 50 . The implant  690  may be utilized in association with either a full or partial knee replacement. Alternatively, the implant  690  could be utilized in association with a repair of a glenoid joint, an elbow, an ankle, a spine or any desired joint in a patient&#39;s body. Implant  690  includes a base  692  and an articular layer  694 . The base  692  has been illustrated in  FIG. 50  as being connected with the proximal end portion  212  of a tibia  214 . The implant  690  is intended for use in association with either a partial or full knee replacement. However, it should be understood that an implant having a construction corresponding to the construction of the implant  690  could be utilized in association with any desired joint in a patient&#39;s body. 
     The base  692  ( FIG. 50 ) is connected with the tibia  214  by projection  700  and a fastener  702 . The projection  700  has a generally cylindrical configuration and extends from a main section  706  of base  692 . The projection  700  extends at an acute angle to the main section  706  in a direction away from the fastener  702 . 
     When the implant  690  is positioned on the proximal end portion  212  of the tibia  214 , the implant is moved along a path which extends parallel to a longitudinal central axis of the projection  700 . The path of movement of the implant  690  onto the proximal end portion  212  of the tibia  214  is indicated by an arrow  707  in  FIG. 50 . The arrow  707  is skewed at an acute angle to a longitudinal central axis of the tibia  214 . This results in the projection  700  being forced into the bone of the proximal end portion  212  of the tibia  214 . Deformation of the bone occurs adjacent to a leading end of the projection  700 . There is no significant deformation of the adjacent to a longitudinally extending outer side surface of the generally cylindrical projection  700 . 
     As the implant  690  is moved into position on the proximal end portion  212  of the tibia  214 , a downwardly extending flange  708  connected with the main section  706  moves into engagement with an outer side surface area on the tibia  214  as the main section  706  of the implant  690  moves into engagement with flat proximal end surface  710  on the tibia  214 . Once the inner side of the main section  706  has been pressed firmly against the flat end surface  710  on the tibia  214  and the projection  700  is moved to the position illustrated in  FIG. 50 , the fastener  702  is inserted through the flange  708 . The fastener  702  is a screw and engages the proximal end portion  212  of the tibia  214  to securely connect the implant  690  with the tibia. A longitudinal central axis of the fastener  702  extends generally parallel to a longitudinal central axis of the projection  700 . Therefore, as the fastener  702  is tightened to press the flange  708  against the outer side of the tibia  214 , the projection  700  is cammed or forced inward to press the main section  706  against the end surface  710  on the tibia. 
     It is contemplated that the base  692  of the implant  690  may be formed of metal. For example, the base  692  may be formed of porous tantalum. Of course, the base  692  could be formed of a different material if desired. Thus, the base  692  could be formed of a polymer or copolymer if desired. The articular layer  694  is formed of a smooth polymeric material which engages in articular surface on a femur. 
     It is contemplated that the patient&#39;s leg will be in the position illustrated in  FIGS. 2 ,  3  and  25  during positioning of the implant  690  on the proximal end portion of the tibia  214 . The upper portion of the patient&#39;s leg  70  will be supported above the support surface  64  ( FIG. 2 ) by the leg support  80 . The limited incision  114  ( FIG. 6 ) will be formed in the knee portion  76  of the patient&#39;s leg  70 . The patella  120  will be in the offset position of  FIG. 8  during positioning of the implant  690 . The drapery system  100  ( FIGS. 4 and 5 ) will provide a sterile field. The tibial resection guide  218  ( FIG. 21 ) may be used during forming of the flat end surface  710  on the tibia  214 . 
     Expandable Devices 
     In accordance with another feature of the invention, one or more expandable devices  720  and  722  ( FIG. 51 ) may be utilized to move, stretch, or separate body tissue. The expandable devices  720  and  722  may be utilized at any time during a full or partial knee replacement. Thus, the expandable devices  720  and  722  may be utilized to separate body tissue from the distal end portion  124  of a femur  214  before a femoral component or implant  290  is connected with the femur and before the tibial tray  286  and tibial bearing insert  294  are connected with the proximal end portion  212  of the tibia  214 . 
     The expandable devices  720  and  722  may be inserted into the knee portion  76  of the patient&#39;s leg  70  one or more days before either a partial or full knee replacement operation is to be undertaken. Before the surgery is initiated, the expandable device  720  may be expanded to stretch skin  342 , the joint capsule, and other tissue in the anterior of the knee portion  76 . The viscoelastic body tissue is resiliently stretched by the expandable device  720  in the general area where the limited incision  114  ( FIG. 6 ) is to be formed. 
     The incision  114  is subsequently made in the body tissue which has been resiliently stretched by the expandable device  720 . After the surgery on the patient&#39;s leg  70  has been completed, for example, after a full or partial knee replacement in accordance with  FIGS. 8-29 , the incision  114  in the stretched tissue is closed. The body tissue which was previously resiliently stretched by the expandable device  720  can, after closing of the incision  114 , return to its normal or unstretched condition. As this occurs, the length of any scar resulting from the incision  114  decreases. By making the incision  114  in body tissue which has previously been resiliently stretched by the expandable device  720 , the overall effective length of the incision  114  is reduced. 
     The expandable devices  720  and  722  may be resilient balloons which are inflated by a gas, such as air, or resilient bladders which are expanded under the influence of a liquid, such as saline solution. The resilient expandable devices  720  and  722  may be formed of a biodegradable material or a non-biodegradable material. It is contemplated that if the expandable devices  720  and  722  are to be left in the patient&#39;s body, they may advantageously be formed of a biodegradable material. However, if it is contemplated that when the expandable devices are to be removed from the patient&#39;s body during or after surgery, the expandable devices may be formed of a non-biodegradable material. 
     Rather than being inserted into the knee portion  76  prior to formation of the incision  114 , the expandable devices  720  and  722  ( FIG. 51 ) may be inserted into the knee portion immediately after making the incision. The expandable devices  720  and  722  may then be expanded to separate body tissue in the knee portion  76 . The expandable devices  720  and  722  are inserted into the knee portion  76  in a collapsed condition. The expandable devices are expanded after being inserted into the knee portion. 
     For example, the expandable device  720  may be resiliently expanded to stretch the patellar ligament  458  ( FIG. 51 ) and move the patella  120  away from the distal end portion  124  of the femur  126 . Alternatively, the expandable device  720  may be positioned between the femur  126  and the patellar tendon  456 . Expansion of the expandable device  720  would then result in movement of the patellar tendon  456  and patella  120  away from the distal end portion  124  of the femur  126 . Of course, if expandable devices were provided between the distal end portion  124  of the femur and both the patellar tendon  456  and patellar ligament  458 , the patella tendon and ligament would both be moved by expansion of the expandable devices. Positioning of the expandable device  720  between the patellar ligament and/or tendon facilitates subsequent movement of the patella  120  to offset position of  FIG. 8 . As previously noted, expandable device  720  can be used to access the inner surface of the patella  120 . 
     The expandable device  722  ( FIG. 51 ) is disposed in the posterior portion of the knee portion  76  of the leg  70 . Expansion of the expandable device  722  in the posterior portion of the patient&#39;s knee is effective to move the joint capsule and fibrous connective tissue away from the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214 . The expandable device  722  may be expanded immediately after the incision  114  is formed to effect releases of body tissue from the distal end portion  124  of the femur  126  and/or the proximal end portion  212  of the tibia  214 . 
     Expansion of the expandable device  722  is effective to move arteries, nerves and veins in the posterior of the knee portion  76  away from the distal end portion  124  of the femur  126  and proximal end portion  212  of the tibia  214  prior to making of the femoral and/or tibial cuts ( FIGS. 8-29 ). If desired, the expandable device  722  may be maintained in the expanded condition during making of one or more of the femoral and/or tibial cuts. If desired, the expandable device  722  may be provided with a tough surface which would protect arteries, nerves and/or veins during the making of one or more of the femoral and tibial cuts. 
     It should be understood that the expandable device  722  may have a configuration which is different from the configuration illustrated in  FIG. 51 . For example, the expandable device  722  may extend for a greater distance along the posterior of the femur  126  and tibia  214  if desired. Although the implants  286 ,  290  and  294  have been illustrated in  FIG. 51 , it should be understood that the expandable devices  720  and  722  may be used before and/or after installation of the implants. The expandable devices  720  and  722  may be positioned in the knee portion  76  of the patient&#39;s leg  70  with the leg in the flexed condition of  FIGS. 2 and 3  or with the leg in the extended condition of  FIG. 51 . 
     After the femoral component  290  and tibial tray  286  and tibial bearing insert  294  have been positioned in the knee portion  726  of the patient&#39;s leg  70 , the expandable devices  720  and  722  may be utilized to assist the surgeon during ligament balancing. The expandable devices  720  and  722  will also assist the surgeon in obtaining a full range of motion of the knee portion  76 . Thus, the expandable devices  720  and  722  may be expanded, under the influence of fluid pressure, to effect ligament releases or to move tissue out of an interfering relationship with relative movement between the femur  126  and tibia  214 . 
     The expandable devices  720  and  722  may be resiliently expanded under the influence of fluid pressure conducted through conduits to the expandable devices. If the expandable devices  720  and  722  are inserted after the incision  114  is formed in the knee portion  76  of the patient&#39;s leg  70 , the conduits for conducting fluid to and from the expandable devices  720  and  722  may extend through the incision. However, if the expandable devices  720  and  722  are inserted prior to making of the incision  114 , the conduits for conducting fluid to and from the expandable devices may extend through small portals or stab wounds formed in the knee portion of the patient&#39;s leg. It should be understood that the conduits for conducting fluid to and from the expandable devices  720  and  722  may extend through small secondary incisions spaced from the main incision  114  even though the expandable devices  720  and  722  are positioned in the knee portion  76  after making the main incision. 
     The small portals or stab wounds which form secondary incisions are spaced from the location where the main incision  114  is formed. Thus, the conduit for conducting fluid to and from the expandable device  722  may extend through a portal or stab wound formed in the posterior portion of the knee portion  76  of the patient&#39;s leg  70 . Before they are expanded, the contracted expandable devices  720  and  722 , are very small and flexible. The contracted expandable devices  720  and  722  have an appearance similar to a collapsed balloon. The contracted expandable devices are easily moved through the small secondary incisions. 
     It is contemplated that the expandable devices  720  and  722  may be left in the knee portion  76  of a patient&#39;s leg  70  after the incision  114  has been closed. If this is done, the expandable devices  720  and  722  may be utilized to obtain a full range of motion of the patient&#39;s knee  76  during therapy and/or recovery of the patient after the incision has been closed. If the expandable devices  720  and  722  are formed of a non-biodegradable material, it may be desirable to remove the expandable devices after the incision  114  has been closed. If the expandable devices  720  and  722  are formed of a biodegradable material, they do not have to be removed after the incision has been closed. It is contemplated that the expandable devices  720  and  722  may be contracted by piercing the skin  342  and puncturing the expandable devices. 
     It is contemplated that it may be desired to form the expandable devices  720  and  722  (and/or the conduits for inflating expandable devices  720  and  722 ) of a biodegradable material which is absorbable by the patient&#39;s body. If this is done, the expandable devices  720  and  722  may be formed of polyglycolic acid, polylactic acid, or combinations of these materials. It is contemplated that the expandable devices  720  and  722  could be formed of materials which include hyaluronic acid, catgut material, gelatin, cellulose, nitrocellulose, collagen or other naturally occurring biodegradable materials. Although it is believed that it would be preferred to form the expandable devices  720  and  722  of biodegradable materials so that they can be left in the patient&#39;s body and hydrolyzed so as to be absorbed by the patient&#39;s body, it is contemplated that the expandable devices  720  and  722  could be made of a non-biodegradable material if desired. The resiliently expandable devices  720  and  722  may have any of the constructions disclosed in U.S. Pat. Nos. 5,163,949; 5,454,365 and 5,514,153. Of course, the resiliently expandable devices  720  and  722  could have a different construction if desired. 
     Obtaining Range of Motion 
     After the implants  286 ,  290  and  294  have been positioned on the femur  126  and tibia  214  in the manner illustrated schematically in  FIG. 52 , it is contemplated that the range of motion of the knee portion  76  will be checked. During the check of the range of motion of the knee portion  76 , it may be found that the range is unduly limited due to interference between body tissue in the posterior of the knee portion  76  and the implants. The range of motion of the knee portion  76  may be limited by tightness of tendons, ligaments and/or other tissue in the knee portion  76 . 
     Although it is believed that the expandable devices  720  and  722  of  FIG. 51  may be utilized to alleviate these conditions, it may be preferred to use an expandable device  730  ( FIG. 52 ) which is inserted between the tibial bearing insert  294  and the trochlear groove in the femur  126 . Thus, once the implants  286 ,  290  and  294  have been positioned in the knee portion  76  of the patient&#39;s leg  70 , the expandable device  730  may be moved through the incision  114 . The expandable device  730  is then moved between the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214 . 
     The expandable device  730  may be a balloon or bladder which is made of resilient material. When fluid pressure in the expandable device  730  is increased, the expandable device is expanded from a collapsed condition to an extended condition. The resilient material of the expandable device  730  may or may not be stretched when the expandable device  730  is expanded. 
     The expandable device  730  may be moved posteriorly of the implants  286 ,  290  and  294  so as to engage tissue in the posterior portion of the patient&#39;s knee. Alternatively, the expandable device  730  may be positioned between the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214 . It is contemplated that the patient&#39;s leg  70  will be in the position illustrated in  FIGS. 2 and 3  with the patella  120  ( FIG. 52 ) offset when the expandable device  730  is positioned in the knee portion  76 . 
     When the expandable device  730  is moved to the posterior of the patient&#39;s knee portion  76 , expansion of the expandable device  730  applies pressure against tissue in the posterior portion of the patient&#39;s knee. This results in movement of body tissue away from the implants  286 ,  290  and  294 . Assuming that body tissue in the posterior of the patient&#39;s knee portion  76  is interfering with the range of relative movement between the implants  286 ,  290  and  294 , applying pressure against the body tissue in the posterior of knee portion will move the body tissue away from the implants to enable the range of motion to be increased. 
     Expansion of the expandable device  730  is effective to move and stretch body tissue, such as the joint capsule, ligaments, tendons, skin or other tissue associated with the posterior portion of the patient&#39;s knee. Space is established between the distal end portion  120  of the femur  126  and body tissue. Space is also established between the proximal end portion  212  of the tibia  214  and body tissue. Since the body tissue is moved and stretched by expansion of the expandable device  730 , a portion of the space tends to remain even though the viscoelastic body tissue retracts when fluid is conducted from the expandable device  730  and the size of the device decreases. 
     The expandable device  730  may be left in place in the posterior of the patient&#39;s knee portion  76  after the incision  114  is closed. A conduit  734  connected with the expandable device  730  would extend through the closed incision  114  to enable fluid to be conducted to and from the expandable device  730 . Therefore, after the incision  114  has been closed, the expandable device  730  can be expanded to increase the range of movement of the knee portion  76  of the patient&#39;s leg  70 . After fluid has been conducted from the expandable device through the conduit  734 , the size of the expandable device is reduced by exhausting fluid through the conduit. The reduced size of the expandable device enables the conduit  734  to be pulled outward, away from the knee portion  76 , to pull the expandable device  730  through a very small opening in the closed incision. 
     If desired, the expandable device  730  could be formed of a biodegradable material and left in the posterior of the knee portion  76 . The conduit  734  could be formed of a non-biodegradable material and pulled from the opening in the incision after the expandable device  730  has at least started to degrade. Of course, the conduit  734  could also be biodegradable. 
     Rather than applying force against body tissue at the posterior of the knee portion  76 , the expandable device  734  may be utilized to apply force against the distal end portion  124  of the femur  126  and against the proximal end portion  212  of the tibia  214 . This force would tend to stretch or release ligaments or other fibrous connective tissue connected with the femur  126  and tibia  214 . This force would also stretch the joint capsule, collateral ligaments  590  and  592  ( FIG. 41 ), and other tissues around the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214 . 
     When this is to be done, the expandable device  730  ( FIG. 52 ) is moved to a position midway between posterior and anterior portions of the implants  286 ,  290  and  294 . The expandable device  730  is then expanded under the influence of fluid pressure conducted through the conduit  734 . As the expandable device expands, it acts as a joint jack to apply force against the femur  126  and tibia  214 . This force will tend to stretch the collateral ligaments and other ligaments and tendons connected with the femur  126  and tibia  214 . 
     Once the expandable device  730  has been utilized to apply an upwardly directed force (as viewed in  FIG. 52 ) against the distal end portion  120  of the femur  126  and a downwardly directed force (as viewed in  FIG. 52 ) against the proximal end portion  212  of the tibia  214 , the expandable device  730  is contracted by conducting a flow of fluid from the expandable device through the conduit  734 . The surgeon can then check ligament balancing and/or the range of motion of the knee portion  76 . If the ligament balancing check and/or range of motion check indicates that it would be beneficial, the expandable device  730  can again be utilized to apply force against the femur  126  and tibia  214 . Fluid pressure would again connected through the conduit  734  to the expandable device  730 . Expansion and contraction of the expandable device  730  can be repeated as many times as necessary to obtain the desired ligament balancing and/or range of motion of the knee portion  76 . 
     In  FIG. 52 , the leg  70  of the patient is in the position indicated in  FIGS. 2 ,  3  and  25 . However, the leg  70  of the patient could be moved from the flexed position of  FIG. 52  to the extended condition of  FIG. 51  with the expandable device in position between the distal end portion  120  of the femur  126  and the proximal end portion  212  of the tibia  214 . It should be understood that the expandable devices  720 ,  722  and  730  of  FIGS. 51 and 52  may be utilized with the leg  70  of the patient in either the extended orientation of  FIG. 51  or the flexed orientation of  FIG. 52 . The leg  70  of the patient may be maintained stationary after insertion of the expandable devices  720 ,  722  and/or  730 . Alternatively, the patient&#39;s leg  70  may be moved in any one or a combination of the directions indicated by the arrows  256 ,  258 ,  259  and  260  in  FIG. 25  after insertion of the expandable devices  720 ,  722  and/or  730 . 
     Although a single expandable device  730  is illustrated in  FIG. 52 , it should be understood that a plurality of expandable devices  730  could be inserted into the knee portion  76  of the patient&#39;s leg. A first one of the expandable devices  730  may be inserted into the posterior of the knee portion  76 . A second expandable devices  730  may be positioned between the lateral portions of the femur  126  and tibia, that is, in a position similar to the position of the transducer  596  in  FIG. 41 . A third expandable device  730  may be positioned between medial portions of the femur  126  and tibia  214 , that is, in a position similar to the position of the transducer  598  in  FIG. 41 . 
     It is contemplated that different pressures may be conducted to the expandable devices in different positions in the knee portion  76 . For example, a relatively low fluid pressure may be conducted to the first expandable device  730  in the posterior of the knee portion  76  to move and/or stretch body tissue with a limited force. A relatively high fluid pressure may be conducted to the second and third expandable devices  730  disposed between the femur  126  and tibia  214  to effect relative movement between the femur and tibia. 
     If desired, a higher fluid pressure could be conducted to one of the expandable devices  730  disposed between the femur  126  and tibia  214  than the other expandable device. For example, a higher fluid pressure may be conducted to the second expandable device  730  disposed between lateral portions of the femur  126  and tibia  214  than to the third expandable device  730  disposed between the medial portions of the femur and tibia. Alternatively, a higher fluid pressure may be conducted to the third expandable device  730  disposed between medial portions of the femur  126  and tibia  214  than to the second expandable device  730  disposed between lateral portions of the femur  126  and tibia  214 . 
     When a plurality of expandable devices  730  are used, the expandable devices may be made of the same material or different materials. For example, the first expandable device  730  in the posterior of the knee portion may be fanned of a biodegradable material. The second and third expandable devices  730 , located between the femur  126  and tibia  214 , may be formed of a non-biodegradable material. Alternatively, the expandable devices  730  may all be formed of the same biodegradable material as the expandable devices  720  and  722 . 
     It is contemplated that the expandable devices  720 ,  722  and/or  730  of  FIGS. 51 and 52  may be utilized in association with many different joints in a patient&#39;s body. For example, the expandable devices may be utilized in association with surgery on a glenoid joint. Alternatively, the expandable devices may be used in association with surgery on a patient&#39;s spine. During spinal surgery, the expandable devices  720 ,  722  and/or  730  may be utilized to move one vertebra relative to an adjacent vertebra during replacement of an intravertebral disc between the vertebrae. If desired, the expandable devices  720 ,  722  and  730  could be positioned between articular processes on vertebrae. When the expandable devices  720 ,  722  and  730  are formed of a biodegradable material, they may be positioned relative to a patient&#39;s vertebral column during surgery and left in place after the surgery. This would allow at least partial healing after the surgery with the expandable devices being effective to transmit force between components of the patient&#39;s vertebral column. 
     The manner in which the expandable devices  720 ,  722  and  730  may be utilized in association with any one of many joints in the patient&#39;s body is similar to that disclosed in U.S. patent application Ser. No. 09/526,949 filed on Mar. 16, 2000. The manner in which an expandable device similar to the expandable devices  720 ,  722  and  730  may be placed within a shoulder joint is similar to the disclosure in the aforementioned application Ser. No. 09/526,949 of which this application is a continuation-in-part. The expandable devices  720 ,  722  and  730  may be utilized during carpal tunnel surgery in the manner disclosed in the aforementioned application Ser. No. 09/526,949. It is believed that it will be particularly advantageous to make the expandable devices  720 ,  722  and  730  of biodegradable material so that they may be left in a patient&#39;s body at the end of the surgery. 
     As previously mentioned, the expandable devices  720 ,  722  and  730  may be utilized during therapy after surgery to stretch body tissue in the knee portion  76  of the patient&#39;s leg  70  and/or to increase the range of motion of the knee portion. It is contemplated that an orthosis may be utilized to stretch tissue that limits joint movement. The orthosis may have a construction similar to the construction disclosed in U.S. Pat. No. 5,611,764. The orthosis may be utilized to affect static progressive stretching of tissue in the knee portion  76  of the patient&#39;s leg  70 . In addition, the orthosis may be utilized during progressive stress reduction. The orthosis may be utilized in conjunction with one or more expandable devices corresponding to the expandable devices  720 ,  722  and  730  in the patient&#39;s knee portion. Alternatively, the orthosis may be utilized without providing expandable devices in the patient&#39;s knee portion. 
     It is contemplated that, during restoration of the range of motion of the knee portion  76 , a constant passive motion device may be connected with the patient&#39;s leg. The constant passive motion device may include one or more load or force limiting devices similar to those disclosed in U.S. Pat. No. 5,456,268. The constant passive motion device may have a construction similar to that illustrated in U.S. Pat. No. 5,285,773. Of course, the constant passive motion device may have a different construction if desired. It is contemplated that a pulsatile stocking may be utilized to reduce the possibility of blood clots while a constant passive motion machine is utilized to increase the range of motion of the knee portion of a patient&#39;s leg. 
     It is contemplated that a laminar spreader may be used in association with the knee portion  76  during ligament balancing and/or gap balancing with the implants  286 ,  290  and  294 . Alternatively, a distraction device which is spring loaded may be utilized on a medial, lateral or both sides of the knee portion  56  rather than the expandable elements  720 ,  722  and  730  to increase range of motion and/or provide a desired ligament balancing. Insol&#39;s technique may be utilized in establishing a desire range of motion of the knee portion  76  of the patient&#39;s leg  70 . 
     Surgical Procedure 
     In the foregoing description of a specific surgical procedure which may be utilized in association with a knee portion  76  of a patient&#39;s leg, the femoral and tibial cuts are made, the patella is repaired and implants are installed in the knee portion  76  of the leg  70 . However, it is contemplated that the various steps in this surgical operation may be performed in a different order if desired. 
     Immediately after the limited incision  114  ( FIG. 6 ) is made in the knee portion  76  in the manner previously explained, repair of the patella  120  may be undertaken. During repair of the patella  120 , the patient&#39;s leg  70  is in the position illustrated in  FIGS. 2 and 3 . The patella  120  is cut in situ with the guide assembly  464  ( FIG. 36 ). After a flat surface has been cut along the plane  484  ( FIG. 35 ) to form a flat surface on the inside of the patella, a layer on which the inner side  122  of the paella is disposed is removed. This decreases the thickness of the paella. 
     After the patellar cut has been made, in the manner previously explained and before installation of the patellar implant, the tibial cut is undertaken. During the tibial cut, the patient&#39;s leg  70  is in the position illustrated in  FIGS. 2 and 3 . The proximal end portion  212  of the tibia  214  is cut, in the manner illustrated schematically in  FIG. 21 . 
     While the tibial cut is being made, the patella  120  is offset from its normal position with the flat cut surface, previously formed on the inner side of the patella, facing toward the distal end portion  124  of the femur  126 . Since the patellar cut has already been made, the patella  120  is relatively thin and provides minimal stretching of the skin  342  and other tissues in the knee portion  76  when the patella is in the offset position of  FIG. 21  during the making of the tibial cut. 
     After the tibial cut has been made, the femoral cuts are made. Making of the femoral cuts after making of the tibial cut and after making of the patellar cut maximizes the space which is available for the making of the femoral cuts. During the making of the femoral cuts, the patient&#39;s leg  70  is in the position illustrated in  FIGS. 2 and 3 . After the tibial cut has been made, a layer is removed from the tibia and the cut surface  246  ( FIGS. 22 and 23 ) on the proximal end portion  212  of the tibia is spaced from the distal end portion  124  of the femur  126 . In addition, the patellar cut has been made so that the patella  120  is relatively thin and provides minimal interference. The femoral cuts are made in the manner previously explained in conjunction with  FIGS. 8-20 . 
     After the femoral cuts have been made, the tibial tray  286  is positioned on the distal end portion  212  of the tibia  214  in the manner illustrated schematically in  FIGS. 27 and 28 . After the tibial tray  286  has been positioned on the tibia  214 , the femoral implant  290  ( FIG. 29 ) is positioned on the distal end portion  124  of the femur  126 . After the femoral implant  290  has been positioned on the distal end portion  124  of the femur  126 , the tibial bearing insert  294  ( FIG. 29 ) is positioned on the tibial tray  286  in the manner previously explained. 
     Once the tibial and femoral implants  286 ,  290  and  294  have been positioned, the patellar implant is mounted on the cut surface of the patella  120 . The patellar implant is positioned on the cut surface of the patella  120  while the patella is in the medially offset position illustrated in  FIG. 29 . By applying force to the patella pulling it outward away from the distal end portion  124  of the femur  126 , a patellar implant can be moved between the patella  120  and the femoral implant  290  ( FIG. 29 ) and mounted on the patella  120 . When the patella  120  has been moved back to the normal or initial position illustrated in  FIG. 6 , the implant on the patella is aligned with the distal end portion  124  of the femur  126 . 
     By making the patellar cut before making of the tibial cut and the femoral cuts, the available space for the tibial cut and femoral cuts is maximized. Maximization of the space for the tibial cut and femoral cuts and for the insertion of the femoral implant  290  and tibial implants  286  and  294  is maximized by mounting the patellar implant after the femoral and tibial implants have been mounted. 
     It should be understood that the foregoing procedure is performed with the patient&#39;s leg in the position illustrated in  FIGS. 2 ,  3  and  25 . Thus, the upper portion  72  of the patient&#39;s leg is supported above the support surface  64  by the leg support  80 . The lower portion  68  of the patient&#39;s leg is suspended from the upper portion  72  of the patient&#39;s leg. The foot  74  is disposed below the support surface  64 . 
     Femoral Cutting Guide 
     A femoral cutting guide  750  ( FIG. 53 ) has cutting guide slots  752  and  754  with open ends  756  and  758 . The guide slot  752  has parallel guide surfaces  762 . Similarly, the guide slot  754  has parallel guide surfaces  764 . 
     The guide surfaces  762  for the guide slot  752  are skewed at an acute angle of forty-five degrees to a major side surface  766  of the femoral cutting guide  750 . Similarly, the guide surfaces  764  are skewed at an angle of forty-five degrees to the major side surface  756  of the femoral cutting guide  750 . The guide surfaces  762  extend perpendicular to the guide surfaces  764 . The guide surface  762  guide a saw blade during the making of an anterior chamfer resection on the distal end portion  124  of the femur  126 . Similarly, the guide surfaces  764  guide a saw blade during the making of a posterior chamfer cut on the distal end portion  124  of the femur  126 . 
     The femoral cutting guide  750  has an anterior guide surface  770  which guides movement of a saw blade during the making of an anterior resection on the distal end portion  124  of the femur  126 . Anterior guide surface  770  extends across the femoral cutting guide  750  between the lateral end portion  774  and a medial end portion  776  of the femoral cutting guide  750 . The anterior guide surface  750  extends perpendicular to the major side surface  766  of the femoral cutting guide  750 . 
     A posterior guide surface  780  guides movement of a saw blade during the making of a posterior resection on the distal end portion  124  of the femur  126 . The posterior guide surface  780  extends between the lateral end portion  774  and the medial end portion  776  of the femoral cutting guide  770 . The posterior guide surface  780  extends perpendicular to the major side surface  766  and extends parallel to the anterior guide surface  770 . The anterior guide surface  770  and the posterior guide surface  780  extend transverse to the guide surfaces  762  and  764  of the guide slots  752  and  754 . 
     The femoral cutting guide  750  is disposed on the distal end of the femur  126 . The femoral cutting guide  750  is connected with the distal end of the femur  126  by a pair of pins  784  and  786 . The pins  784  and  786  have longitudinal central axes which extend perpendicular to the major side surface  766  of the femoral cutting guide  750  and extend generally parallel to a longitudinal central axis of the femur  126 . 
     When the femoral cuts are to be made on the distal end portion  124  of the femur  126 , the femoral cutting guide  750  is connected to the distal end of the femur. Initial portions of the various femoral cuts are then made by moving the saw blade along the guide surfaces  762 ,  764 ,  770  and  780  on the femoral cutting guide  750 . Since the femoral cutting guide  750  extends only part way across the distal end portion  124  of the femur  126 , the femoral cutting guide is disconnected from the femur and the femoral cuts are completed. 
     After the femoral cutting guide  750  has been disconnected from the femur  126 , cut surfaces during formation of the initial portion of the anterior femoral cut are utilized to guide the saw blade during completion of the anterior femoral cut. Similarly, cut surfaces formed during the initial portion of the posterior femoral cut are utilized to guide the saw blade during completion of the posterior femoral cut. Cut surfaces formed during the making of anterior chamfer cut are utilized to guide the saw blade during completion of the anterior chamfer cut. Similarly, cut surfaces formed during making of the initial portion of the posterior chamfer cut are utilized to guide the saw blade during completion of the posterior chamfer cut. 
     The cutting tool which is used to form the femoral cuts, tibial cuts, and patellar cut may have any desired construction. Although a saw  172  and blade  170  have been disclosed herein as making the various cuts, many known types of cutting tools may be used if desired. For example, laser cutters, milling cutters, and/or ultrasonic cutters may be utilized. When one or more features of the present invention are utilized to perform knee joint revisions, an ultrasonic cutter may advantageously be utilized to cut cement previously used in association with an implant. 
     Side Cutting Guide 
     Using the femoral cutting guide  210  of  FIG. 19  or the femoral cutting guide  750  of  FIG. 53 , the femoral cuts are made by moving a saw blade from a distal end of the femur  126  toward a proximal end of the femur. However, it is contemplated that the femoral cuts could be made by moving a saw blade between opposite sides of the femur in a direction extending generally perpendicular to a longitudinal central axis of the femur. Thus, the saw blade is moved along a path which extends between lateral and medial surfaces on the distal end portion  124  of the femur  126 . 
     A femoral cutting guide  800  is illustrated in  FIG. 54  as being mounted on a lateral surface  802  of the femur  126 . However, the femoral cutting guide  800  could be mounted on the medial surface of the femur  126  if desired. When the cutting guide  800  is mounted on the lateral surface  802  of the femur  126 , the incision  114  ( FIG. 6 ) is laterally offset. Similarly, when the cutting guide  800  is mounted on a medial surface of the femur  126 , the incision  114  is medially offset. 
     The femoral cutting guide  800  has a distal guide surface  806 . The distal guide surface  806  is disposed in a plane which extends perpendicular to a longitudinal central axis of the femur  126  and extends through the lateral and medial condyles. The distal guide surface  806  extends perpendicular to a major side surface  808  of the femoral cutting guide  800 . 
     An anterior chamfer guide surface  812  extends between opposite major sides of the femoral cutting guide  800 . The anterior chamfer guide surface  812  is disposed in a plane which extends at an acute angle of forty-five degrees to a plane containing the distal guide surface  806 . The anterior chamfer guide surface  812  extends perpendicular to the major side surface  808  of the femoral cutting guide  800 . Similarly, a posterior chamfer guide surface  816  extends between opposite major sides of the femoral cutting guide  800 . The posterior chamfer guide surface  816  is disposed in a plane which extends at an acute angle of forty-five degrees to a plane containing the distal guide surface  806 . The plane containing the posterior chamfer guide surface  816  extends perpendicular to the plane containing the anterior chamfer guide surface  812 . 
     An anterior guide surface  820  is disposed on the femoral cutting guide  800 . The anterior guide surface  820  extends between opposite major sides of the femoral cutting guide  800 . The anterior guide surface  820  is disposed in a plane which extends perpendicular to a plane containing the distal guide surface  806 . The plane containing the anterior guide surface  820  extends generally parallel to a longitudinal central axis of the femur  126 . 
     Similarly, the femoral cutting guide  800  includes a posterior guide surface  824 . The posterior guide surface  824  extends between opposite major sides of the femoral cutting guide  800 . The posterior guide surface  824  is disposed in a plane which extends parallel to a plane containing the anterior guide surface  820  and perpendicular to a plane containing the distal guide surface  806 . 
     The femoral guide  800  is formed of one piece of metal and has parallel opposite major side surfaces  808 . The femoral cutting guide  800  is connected with the lateral side  802  of the distal end portion  124  of the femur  126  by a pair of pins  830  and  832 . The lateral side  802  of the femur may be cut to form a flat surface which is abuttingly engaged by a major side surface of the femoral cutting guide  800 . 
     When the femoral cuts are to be made, the lateral side of the femur is cut to form a flat side surface on which the femoral cutting guide  800  is mounted by the pins  830  and  832 . A saw blade or other cutting tool is then moved from the lateral side to the medial side of the distal end portion  124  of the femur  126  while the saw blade or other cutting tool is guided by the distal guide surface  806  on the femoral cutting guide  800 . The distal guide surface  806  has an extent which is less than the extent of the distal end cut to be formed on the distal end portion  124  of the femur  126 . Therefore, after an initial portion of the distal end cut has been made utilizing the guide surface  806  to guide movement of a saw blade or other cutting tool, the cut surfaces are utilized to guide movement of the cutting tool during completion of the distal end cut. 
     Once the distal end cut has been completed, the saw blade or other cutting tool is moved from the lateral side of the femur  126  to the medial side of the femur along the anterior chamfer guide surface  812 . The cutting tool is then moved from the lateral side of the femur  126  to the medial side of the femur along the posterior chamfer guide surface  816 . Since the anterior chamfer guide surface  812  and posterior chamfer guide surface  816  have lengths which are less than the length of the anterior chamfer cut and posterior chamfer cut, only the initial portions of the chamfer cuts are made utilizing the guide surfaces  812  and  816  on the femoral cutting guide  800 . The cuts are completed by guiding movement of the saw blade or other cutting tool with the previously cut surfaces. 
     The anterior guide surface  820  is then utilized to guide movement of the saw blade during an initial portion of an anterior cut. During making of the anterior cut, the saw blade or other cutting tool is moved from the lateral side to the medial side of the distal end portion  124  of the femur  126 . Since the anterior guide surface  820  is smaller than the anterior cut, surfaces formed during making of an initial portion of the anterior cut are utilized to guide the saw blade or other cutting tool during a final portion of the anterior cut. 
     Similarly, the posterior guide surface  824  on the femoral cutting guide  800  is utilized to guide the saw blade or other cutting tool during making of a posterior cut. During the making of an initial portion of the posterior cut, the saw blade is moved along the posterior guide surface  824  from the lateral side  802  of the distal end portion  124  of the femur  126  to the medial side. The posterior guide surface  824  is shorter than the posterior cut. Therefore, cut surfaces formed during an initial portion of the posterior cut are utilized to guide the saw blade during completion of the posterior cut. 
     The femoral cutting guide  800  remains connected with the femur  126  during the initial portion of each of the femoral cuts and during completion of the femoral cuts. The femoral cutting guide  800  is not of the capture type. Therefore, a saw blade is free to move past the guide surfaces  806 ,  812 ,  816 ,  820  and  824  during completion of the femoral cuts. If the guide surfaces  806 ,  812 ,  816 ,  820  and  824  were formed by slots, the femoral cutting guide  800  would have to be disconnected from the femur before the femoral cuts could be completed. 
     The femoral cutting guide  800  has been illustrated in  FIG. 54  as being mounted on the lateral side  802  of the femur  126 . However, it is contemplated that the femoral cutting guide could be mounted on the medial side of the femur if desired. The distal cuts, chamfer cuts, anterior cuts and posterior cuts were set forth as being performed in that order. However, there is no critical order as to the sequence of the cuts. It is contemplated that the cuts may be formed in any desired sequence. 
     During use of the femoral cutting guide  800 , the patient&#39;s leg  70  can be in the orientation illustrated in  FIGS. 2 ,  3  and  25 . The drapery system  100  can be utilized to maintain a sterile field during the operation on the patient&#39;s leg. 
     Optical Systems 
     Rather than using the guide members illustrated in  FIGS. 9-21 , it is contemplated that an optically created guide could be utilized. The optically created guide may be a three dimensional image created by projecting a hologram onto an end portion of a bone which is to be cut. For example, a hologram may be used in projecting a three dimensional image of any one of the guides  138  ( FIG. 11 ),  186  ( FIG. 17 ),  210  ( FIG. 20 ), and  218  ( FIG. 21 ) onto a femur  126  or tibia  214  in a patient&#39;s body. Alternatively, one or more beams of coherent or non-coherent light may be projected onto the bone which is to be cut to provide a two dimensional cutting guide. 
     Utilizing pre-operative templating based on images of one or more bones in a patient&#39;s body, for example, a distal end portion  124  ( FIG. 55 ) of a femur  126 , a hologram may be developed. The hologram is utilized with a projector  858  to create a three dimensional image  850 . The illustrated three dimensional image is of a pattern of cuts to be made on the distal end portion of the femur  126 . In  FIG. 55 , the three dimensional image  850  is visible to the surgeon  106  and is utilized to replace the femoral cutting guide  800  of  FIG. 54 . Rather than replacing the femoral cutting guide  800  with a pattern of cuts as shown in  FIG. 55 , the three dimensional image  850  may be an image of the femoral cutting guide  800 . 
     Although a hologram may be used to produce the three dimensional image  850  which is visible to the surgeon  106 , the image may be created in other ways if desired. When the visible image  850  is to be projected onto a flat surface cut on the distal end portion  124  of the femur  126 , a two dimensional image may be utilized if desired. The two dimensional image  850  may be accurately projected on to the flat surface on the end portion  124  of the femur  126  utilizing either coherent or non-coherent light and known image projection techniques. 
     The three dimensional image  850  has visible light beams  852  and  854  which define opposite ends of a sight line for guidance of a saw  172  or other cutting tool. If desired, light may be projected with a plane of colored light which extends between the light beams  852  and  854 . The colored light plane extending between the light beams  852  and  854  is visible and provides a guide for alignment of a blade  170  in a desired spatial orientation relative to the side surface  802  on the femur  126 . 
     The surgeon  106  moves the saw blade  170  along the colored plane of light extending between the light beams  852  and  854 . The colored plane of light extending between the light beams  852  and  854  indicates to the surgeon the desired spatial orientation of the saw blade  170  during the making of a cut. A sensor connected with the saw  172  enables a computer connected with a source  858  of the image  850  to have the plane of light extend along each of the desired saw cuts during the making of the saw cut. Thus, during the making of the femoral cut which extends between the light beams  852  and  854 , a plane of colored light extends between the light beams. This enables the surgeon to determine when the saw blade is properly aligned with the side surface  802  of the femur  126 . When a different cut is to be made, for example, a cut between the light beam  852  and a light beam  862 , a plane of colored light extends between the light beams  852  and  862 . The plane of light is visible and indicates to the surgeon the desired spatial orientation of the blade  170  of the saw  172  relative to the femur  126 . 
     In addition, locating laser light beams  866  and  868  are projected from laser light sources  872  and  874  mounted on the saw  172 . The locating laser light beams  866  and  868  are visible to the surgeon  106  and are of a different color than the plane of light extending between the light beams  852  and  854  of the image  850 . Therefore, a surgeon can visually determine when the locating laser light beams  866  and  868  are aligned with the plane of light extending between the light beams  852  and  854  of the image  850 . 
     When the locating laser light beams  866  and  868  are disposed in the plane of light extending between the light beams  852  and  854 , the saw blade  170  is accurately aligned with the portion of the femoral cut to be made between the light beams  852  and  854  of the image  850 . If the locating laser light beams  866  and  868  are not disposed in the plane of light extending the light beams  852  and  854 , the saw blade  170  is not in alignment with the desired location for the femoral cut. 
     In addition to the visual indication provided by alignment of the locating laser light beams  866  and  868  with the plane of light between the light beams  852  and  854 , audible and/or visual signals may be provided to the surgeon indicating whether or not the locating laser light beams  866  and  868  are in alignment with the plane of colored light extending between the light beams  852  and  854 . For example, a green light may be illuminated when the locating laser light beams  866  and  868  are in the same plane as the light beams  852  and  854  of the image  850 . A red light may be illuminated when either or both of the locating laser light beams  866  and  868  are not located in the plane of colored light extending between the light beam  852  and the light beam  854 . In addition, a warning sound, that is, an alarm, may be sounded when either one of the locating laser light beams  866  or  868  is offset from the plane of colored light extending between the light beams  852  and  854 . 
     Once the femoral cut extending between the light beams  852  and  854  has been completed, the saw  172  and saw blade  170  are moved into alignment with a plane of colored light extending between the light beam  852  and  862 . A second femoral cut is then made in the same manner as previously described in conjunction with the light beams  852  and  854 . This process is repeated until the desired number of femoral cuts have been made. 
     In the embodiment illustrated in  FIG. 55 , the image  850  is projected onto a side surface  802  of the femur  26 . If desired, a three dimensional image may be projected onto all sides of the distal end portion  124  of the femur  126 . If this is done, the image may advantageously be a three dimensional image formed by lines which define the cuts to be made. As the saw blade  170  moves along lines of the three dimensional image, the saw blade  170  is moved to orientations corresponding to the orientations of the saw blade when making the femoral cuts illustrated in  FIGS. 12-23 . However, rather than using the cutting guides illustrated in  FIGS. 12-23 , the three dimensional image, corresponding to the image  850  of  FIG. 55 , is projected onto the entire distal end portion  124  of the femur  126 . Locating laser light beams would be projected from the saw  172  to indicate to a surgeon when a saw was in the desired orientation relative to light planes forming portions of the image projected onto the distal end  874 . This enables the saw blade  170  to be located relative to the distal end  874  of the femur  126  in the same manner as previously explained in conjunction with the side surface  802  of the femur. 
     As was previously mentioned, the three dimensional image  850  may be an image of anyone of the guides  138 ,  186 ,  210 ,  500 ,  750  or  800 . The saw blade  170  would be moved along the image of a guide surface on the three dimensional image of the guide. The locating laser light beams  866  and  868  would indicate to the surgeon the orientation of the saw blade  170  relative to the three dimensional image of a guide surface on the three dimensional image of any one of the guides  138 ,  186 ,  210 ,  218 ,  500 ,  750  or  800 . This would eliminate the heavy metal guides which have previously been used. When the size of any one of the three dimensional images of one of the guides  138 ,  186 ,  210 ,  218 ,  500 ,  750  or  800  is to be changed, it is merely necessary to have a computer controlling the projection of the three dimensional image to change a hologram being used to project the image or to effect a change in optics through which the image is projected. 
     Once the femoral cuts have been completed, an optical measuring device, such as an interferometer, may scan the cuts to determine if they have the desired configuration. Scanning the cuts with an optical measuring device may be used to eliminate the necessity of performing trials with provisional components. Eliminating the necessity of utilizing provisional components substantially reduces the amount of equipment required during a partial or total knee replacement. 
     The cut surfaces on the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214  are illustrated in  FIGS. 22 and 23 . Rather than performing trials with provisional implants, the cut surfaces on the femur  126  and tibia  214  are measured using known optical measuring devices. A computer, connected with the optical measuring device, is utilized to compare the measurement of the cut surfaces on the femur  216  and the tibia  214  with desired measurements for the specific implants  286 ,  290  and  294  to be mounted on the femur and tibia. The computer also compares optically determined orientations of the cut surfaces on the femur  126  and tibia  214  relative to desired orientations of the cut surfaces. 
     The optical measuring device may have any one of many known constructions. For example, the optical measuring device may have the construction illustrated in U.S. Pat. No. 6,185,315 or 6,195,168 if desired. If an optical measuring device or other measuring device indicates that the cut surfaces are incorrect, a computer connected with the source  858  ( FIG. 55 ) of the image  850  will change the hologram to correspond to a next smaller size of implant. When a surgeon determines that the femur  126  should be cut for the next smaller size implant, the surgeon manually enters data into the computer. In response to this data, the computer causes the projector  858  of the image  850  to project an image corresponding to a next smaller size image. The saw  172  is then utilized to cut the femur along the lines indicated by the next smaller size image. This will allow the next smaller size implant to be mounted on the femur. 
     It is contemplated that the projector  858  could have any desired construction. For example, the projector  858  could have a construction which is generally similar to the construction of apparatus disclosed in U.S. Pat. No. 6,211,976. It is contemplated that the laser light sources  872  and  874  could have a construction similar to the construction of devices disclosed in U.S. Pat. No. 5,425,355. The laser light sources  872  and  874  may have a construction which is similar to the construction of devices which are commercially available from Laserscope, Inc. of San Jose, Calif. 
     It is contemplated that the patient&#39;s leg  70  will be in the position illustrated in  FIGS. 2 and 3  when either the two dimensional or the three dimensional image is projected onto the end portion  124  of the femur  126 . The relatively small incision  114  may be resiliently expanded and/or moved relative to the distal end portion  124  of the femur  126  to allow the image  850  to be sequentially projected onto various areas on the distal end portion  124  of the femur  126 . A three dimensional image may be generated by any one of several known methods, including the method disclosed in U.S. Pat. No. 5,379,133. 
     It is contemplated that the three dimensional image  850  may be used with procedures other than cutting of one or more bones in a patient&#39;s leg  70 . For example, a three dimensional image of cuts to be made on a vertebra in a patient&#39;s back may be projected onto the vertebra. The three dimensional image may be used in surgery involving soft tissue in a patient&#39;s body. For example, the three dimensional image may be projected to a location in a patient&#39;s body where a vascular anastomosis or an intestinal anastomosis is to be undertaken. The three dimensional image may correspond to a pattern of stitches to be made between portions of soft body tissue. By projecting the three dimensional image into a patient&#39;s body at any desired location where surgery of any type is to be undertaken, a guide is provided in the patient&#39;s body to assist the surgeon. 
     The locating laser light beams  852  and  854  may be used with surgical instruments other than the saw  172 . For example, the locating laser light beams  852  and/or  854  could be utilized to indicate the position of a bovie, or a needle, or forceps relative to body tissue. The locating laser light beams may have an intensity which is sufficient to shine through body tissue and enable a surgeon on one side of body tissue to visually determine the position of a surgical instrument on the opposite side of the body tissue. 
     Unicompartmental Knee Replacement 
     The drawings associated with the foregoing description have illustrated a full knee replacement rather than a partial knee replacement. However, it is contemplated that the previously described features of the present invention may be utilized with either a partial knee replacement or a full knee replacement. A femur  126  is illustrated schematically in  FIG. 56  and has a distal end portion  124  with a pair of condyles  890  and  892 . When a partial knee replacement is to be made, only one of the two condyles, that is the condyle  892 , is cut. A saw  172  having a blade  170  is used to cut the condyle  892  along a line indicated at  896  in  FIG. 56 . 
     The saw  172  is provided with laser light sources  902  and  904 . The laser light sources  902  and  904  project visible locating laser light beams  906  and  908  which extend along opposite longitudinal edges of the saw blade  170 . The locating laser light beams  906  and  908  impinge against the condyle  892 . The locating light beams are of colored coherent light which is visible to a surgeon to indicate the orientation of the saw blade  170  relative to the condyle  892 . 
     It is contemplated that the saw  172  and blade  170  may be utilized in association with a guide member which is connected with the femur  126 . Alternatively, a two or three dimensional image, corresponding to the image  850  of  FIG. 55 , may be projected onto the distal end portion of the femur  126 . Another alternative would be to make a line  896  on the condyle  892  with a marking instrument. 
     Rather than using a saw blade  170  to make the cut in the condyle  892 , it should be understood that a different type of cutting tool could be utilized if desired. For example, a milling cutter could be used to cut along a line  896  in  FIG. 56 . If a full knee replacement, rather than a partial knee replacement, is desired, both condyles  890  and  892  may be cut with the saw  172  and blade  170  using the laser light sources  902  and  904  to indicate the position of the saw blade relative to the distal end portion  124  of the femur  126 . Once the femoral cuts have been made, an optical measuring device may be utilized to determine whether or not the cuts are of the proper size. 
     Multiple Incisions 
     A single incision  114  is illustrated in  FIGS. 6-8  to provide access to the knee portion  76  of the patient&#39;s leg  70 . As has been previously explained herein, the length of the incision  114  is minimized. However, it is contemplated that the length of the incision  114  could be further reduced by providing one or more very small incisions  920  ( FIG. 57 ) in the knee portion  76  of a patient&#39;s leg  70  in association with the incision  114 . The incision  920  is a small stab wound which forms a portal through the skin  342 . The blade  170  of the saw  172  or other cutting tool may be moved through the small incision  920  to make one or more femoral cuts. 
     After the femoral cuts have been made through the small incision  920  and the larger or main incision  114 , femoral and/or tibial implants are moved through the main incision. By providing the small incision  920  in association with the larger main incision  114 , the overall length of the main incision may be minimized. 
     During making of the incisions  114  and  970 , the patient&#39;s leg  70  is in the position illustrated in  FIGS. 2 and 3 . During making of the tibial and femoral cuts and insertion of the implants, the patient&#39;s leg  70  is also in the position illustrated in  FIGS. 2 and 3 . If desired, one or more expandable devices, corresponding to the expandable devices of  FIGS. 51 and 52 , may be inserted through one or more small incisions  920  and/or the main incision  114 . 
     In the embodiment of the invention illustrated in  FIG. 57 , laser light sources  902  and  904  are connected with the saw  172  in the manner illustrated schematically in  FIG. 56 . The laser light sources provide visible locating laser light beams, corresponding to the locating laser light beams  906  and  908  of  FIG. 56 . 
     By using more than one incision, that is, the main incision  114  and one or more small incisions  920 , cutting tools can approach and move along the distal end portion  124  of the femur  126  from different directions. Thus, the saw blade  170  moves from the right to the left as viewed in  FIG. 57 , that is, in a lateral direction, during making of a femoral cut. A cutting tool which moves through the incision  114  may move in a superior direction along the femur  126 , that is, from the distal end portion  124  of the femur  126  toward a proximal end portion of the femur. The cutting tools may be used to make cuts required for either a partial or full knee replacement. 
     Although it is preferred to make the incisions  114  and  920  and to cut the femur  126  with the leg  70  of the patient in the position illustrated in  FIGS. 2 and 3 , it should be understood that the use of a plurality of incisions during the surgery with the leg in other positions may be desired. Although the foregoing description has been in conjunction with surgery on a knee portion of a leg  70  of a patient, it is contemplated that the surgery could be performed on a different portion of the patient if desired. 
     Patellar Tracking 
     A pair of transducers  596  and  598  are illustrated in  FIGS. 41 and 42  to compare tension and collateral ligaments  590  and  592 . The manner in which the transducers  596  and  598  are positioned between the femur  126  and tibia  214  is illustrated schematically in  FIG. 58 . 
     In accordance with another feature of the invention, a pair of patellar transducers  930  and  932  are disposed on an inner side of the patella  120 . The patellar transducers  930  and  932  are connected with a display, corresponding to the computer display areas  601  and  602  of  FIG. 41 . The patellar transducers  930  and  932  are disposed between the distal end portion  124  of the femur  126  and the patella  120 . 
     The patellar transducers  930  and  932  have outputs which correspond to force transmitted between the patella  120  and the femur  126 . Thus, the output from the transducer  930  corresponds to the force transmitted between the lateral side of the patella  120  and a lateral side of a trochlear groove in the femur  126 . Similarly, the output from the transducer  932  corresponds to the force transmitted between a medial side of the patella  120  and a medial side of the trochlear groove in the femur  126 . By comparing the output from the patellar transducers  930  and  932  during relative movement between the femur  126  and tibia  214 , variations in the force transmitted between the lateral and medial portions of the patella  120  can be compared. This enables a surgeon to determine when the patella is tracking properly relative to the femur  126 . 
     The patellar transducers  930  and  932  are resiliently expandable containers which hold fluid. As the force transmitted between the patella  120  and the femur  126  increases, the pressure of the fluid in the patellar transducers  930  and  932  increases. It is contemplated that the containers  930  and  932  may hold either a gas or a liquid. Pressure signals corresponding to the pressure in the patellar transducers  930  and  932  are conducted through conductors  934  and  936  to a display, corresponding to the computer displays  601  and  602  of  FIG. 41 . The patellar transducers  930  and  932  may have any desired construction which enables them to measure the force transmitted between the patella  120  and the femur  126 . Thus, the transducers  930  and  932  could be of the piezoelectric type or of a strain-gauge type. 
     During checking of patellar tracking with the transducers  930  and  932 , the upper portion  72  of the leg  70  of the patient is supported above the support surface  64  by the leg holder  80  ( FIG. 2 ). The leg  70  is moved between the flexed condition of  FIGS. 2 and 3  and the extended condition of  FIG. 4 . During movement of the leg  70  between the flexed and extended conditions, there is relative movement between the end portion  124  of the femur  126  and the patella  120  ( FIG. 58 ). During relative movement between the femur  126  and patella  120 , the output from the patellar transducers  930  and  932  indicates the manner in which force transmitted between the patella and femur varies. This enables a surgeon to detect any defects in tracking of the patella  120  relative to the femur  126 . 
     The patellar transducers  930  and  932  are mounted on the patella  120  after the patellar implant has been mounted on the patella. This enables the patellar transducers  930  and  932  to be utilized to detect any irregularities in the manner in which the patellar implant cooperates with the femoral implant  290  ( FIG. 29 ). However, it is contemplated that the patellar transducers may be mounted on the patella  120  before the patellar implant is mounted on the patella. When this is to be done, the transducers  930  and  932  may be mounted in a body having a size and configuration corresponding to the intended size and configuration of the patellar implant. 
     In the embodiment of  FIG. 58 , the patellar transducers  930  and  932  extend across the patella  120  between lateral and medial edges of the patella. However, it is contemplated that the transducers  930  and  932  may extend only part way across the patella. If desired, more than the two illustrated patellar transducers  930  and  932  may be provided on the patella  120 . 
     The transducers  596  and  598  can be utilized in combination with the patellar transducers  930  and  932  ( FIG. 58 ). This enables the surgeon to determine the manner in which tension varies in the collateral ligaments  590  and  592  ( FIGS. 41 and 42 ) with variations in force transmitted between the patella  120  ( FIG. 58 ) and the femur  126 . However, the patellar transducers  930  and  932  may be utilized without the transducers  596  and  598 . 
     When it is determined that the patella  120  is not tracking properly, corrective action may be taken by increasing the fluid pressure in either or both of the patellar transducers  930  and  932 . If the transducers  596  and  598  are utilized, the corrective action may include increasing the fluid pressure in either or both of the transducers  596  and  598 . The transducers  596  and  598  and the patella transducers  930  and  932  are formed of resilient material which can be expanded under the influence of fluid pressure. 
     Although the patellar transducers  930  and  932  are utilized to measure force transmitted between lateral and medial portions of the patella  120  and the femur  126 , the patellar transducers can be utilized to stretch or move body tissue in the same manner as the expandable devices  720 ,  722  and  730  ( FIGS. 51 and 52 ). By increasing the fluid pressure conducted to the patellar transducer  930  ( FIG. 58 ), the patellar transducer expands to stretch fibrous connective body tissue connected with the lateral side of the patella  120 . Similarly, increasing the fluid pressure conducted to the patellar transducer  932  expands the patellar transducer  932  to stretch fibrous connective body tissue connected with the medial side of the patella  120 . Increasing the fluid pressure conducted to both patellar transducers  930  and  932  is effective to expand both transducers and stretch fibrous connective body tissue with both sides of the patella  120 . 
     The patellar transducers  930  and  932  may be formed of either a biodegradable material or a non-biodegradable material. When the patellar transducers  930  and  932  are to be left in the knee portion  76 , the patellar transducers may be formed of a biodegradable material which is eventually absorbed by the patient&#39;s body. When the patellar transducers  930  and  932  are to be removed from the knee portion  76 , the patella transducers may be formed of a non-biodegradable material. If the patellar transducers  930  and  932  are formed of a biodegradable material and are left in the knee portion  76  after closing of the incision  114 , the patellar transducers may be expanded during therapy to stretch body tissue connected with the patella  120 . 
     Movable Implant 
     The implant  690  of  FIG. 50  is fixedly secured to the proximal end portion  212  of a tibia  214  by the projection  700  and fastener  702 . In the embodiment of the invention illustrated in  FIG. 59 , a moveable implant  950  is provided between the distal end portion  124  of a femur  126  and a proximal end portion  212  of a tibia  214 . In accordance with a feature of this embodiment of the invention, the implant  950  is freely moveable relative to both the femur  126  and the tibia  214 . 
     The moveable implant  950  has a smooth upper (as viewed in  FIG. 59 ) surface  952  which is engaged by a medial portion of the distal end portion  124  of the femur. Similarly, the moveable implant  950  has a smooth lower (as viewed in  FIG. 59 ) surface  954  which is engaged by a medial portion of the proximal end portion  212  of the tibia  214 . This smooth upper and lower end surfaces  952  and  954  compensate for defects in the existing surfaces on the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214 . By providing the moveable implant  950  between the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214 , pain which results from engagement of a surface  958  on the distal end portion  124  of the femur  126  with a surface  960  on the proximal end portion  212  of the tibia  214  is eliminated or at least substantially reduced. 
     During bending of the knee portion  76  of the patient&#39;s leg  70 , the implant  950  may move relative to both the femur  126  and the tibia  214 . The implant  950  can move in either a lateral or medial direction relative to the femur  126  and tibia  214 . In addition, the implant  950  can move in either a posterior or anterior direction relative to the femur  126  and tibia  214 . 
     By having a three hundred and sixty degree (360°) range of movement relative to both the femur  126  and tibia  214 , the moveable implant  950  accommodates relative movement between the femur and tibia with minimal pain. This is because relative movement will occur between the implant  950 , femur  126  and tibia  214  at locations where frictional forces due to irregularities on the surfaces of the femur  126  and tibia  214  are minimal. In addition, the implant  950  can shift relative to the femur  126  and tibia  214  during bending of the knee portion  76  to accommodate irregularities in the existing surfaces  958  and  960  on the distal end portion  124  of the femur and the proximal end portion  212  of the tibia. 
     The range of movement of the implant  950  relative to the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214  is limited by engagement of the moveable implant  950  with soft tissue in the knee portion  76  of the patient&#39;s leg  70 . Therefore, even though the implant  950  can move relative to the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214 , the implant is held against excessive movement relative to the femur and tibia by soft tissues associated with the femur and tibia. 
     For example, engagement of the implant  950  with cartilage or other soft tissue which is located at the peripheral aspect of the knee joint between the femur  126  and tibia  214  retains the implant  950  within a desired range of movement. The cartilage may be articular cartilage and/or fibrocartilage. The cartilage is engaged by peripheral surfaces on the moveable implant  952  and retains the implant in a desired position relative to the femur  126  and tibia  214 . In addition, fibrous connective tissue extending between the femur  126  and tibia  214  limits movement of the implant  950  relative to the femur and tibia. 
     The joint capsule in the knee portion  76  of the patient&#39;s leg may be engaged by the periphery of the implant  950  to retain the implant in a desired position. By using cartilaginous, ligamentous, or other tissues to limit the range of movement of the moveable implant  950 , the implant can freely shift relative to the femur  126  and tibia  214  through a limited range of movement during bending of the knee portion  76  of the patient&#39;s leg  70 . If desired, growth of the tissues used to limit the range of movement of the implant may be promoted. 
     The moveable implant  950  is sized so as to fit the surfaces  958  and  960  on the distal end portion  124  and proximal end portion  212  of the femur  126  and tibia  214  ( FIG. 59 ). The sizing is accomplished by imaging the knee portion  76  of the patient&#39;s leg. The moveable implant  950  may be one of a series of implants of different sizes. After the patient&#39;s knee portion  76  has been imaged, a moveable implant is selected from the series of moveable implants of different sizes. The size of the selected moveable implant closely approximates the size of the space between the surfaces  958  and  960  on the distal end portion  124  and proximal end portion  212  of the femur  126  and tibia  214 . 
     Thus, for a relatively large individual, a moveable implant  950  having a relatively large size is selected from the series of moveable implants. Similarly, for an individual having a relatively small size, a moveable implant  950  having a relatively small size is selected from the series of moveable implants. The selected implant has a size which corresponds to the general size of the space between the surfaces  958  and  960 . 
     As a result of imaging of the knee portion  76  of the patient&#39;s leg  70 , the actual configurations of the existing surfaces  958  and  960  on the femur  126  and tibia  214  can be accommodated by shaping the upper surface  952  of the moveable implant  958  to have a configuration corresponding to the surface  958  on the femur  126 . Similarly, the lower surface  954  on the moveable implant  950  can be shaped to have a configuration corresponding to the configuration of the surface  960  on the tibia  214 . Of course, the configuration of the periphery of the moveable implant can be changed to correspond to the configuration of the periphery of the space between the surfaces  958  and  960  into which the moveable implant  950  is to be placed. 
     It is contemplated that the imaging of the knee portion  76  of the patient&#39;s leg  70  may be done preoperatively, on an out-patient basis. The moveable implant  950  may then be selected from the series of available moveable implants and shaped to have a configuration which corresponds to the configuration of the space between the surfaces  958  and  960 . The implant  950 , which has been shaped to conform to the space between the surfaces  958  and  960 , may then be moved to an operating room for insertion into a patient during the surgical procedure. Alternatively, the imaging of the knee portion  76  and shaping of the moveable implant  950  to the desired configuration may be performed in the operating room as part of the surgical procedure. 
     When the moveable implant  950  is to be positioned in the knee portion  76  of the patient&#39;s leg  70 , in the manner indicated schematically in  FIG. 59 , a limited incision is made in the knee portion of the patient&#39;s leg. The limited incision is made while the patient&#39;s leg  70  is supported in the position shown in  FIGS. 2 ,  3  and  25 . The upper portion of the patient&#39;s leg is supported by the leg support  80 . 
     The incision may have a limited length, corresponding to the limited length of the incision  114  of  FIG. 7  and be located adjacent to an edge of the patella  120 . When the implant  950  is to be positioned adjacent to a medial portion of the femur  126  and a medial portion of the tibia  214 , in the manner illustrated schematically in  FIG. 59 , the incision  114  would be located adjacent to a medial edge of the patella  120 , in the manner illustrated in  FIG. 6 . However, it should be understood that if the implant  950  is to be located adjacent to a lateral portion of the femur  126  and a lateral portion of the tibia  214 , the incision  114  could be formed adjacent to a lateral edge of the patella  120 . 
     Once the limited incision  114  has been formed in the manner previously described in conjunction with  FIGS. 6 and 7  herein, the patella  120  may be moved to the offset position of  FIG. 8  with the inner side  122  of the patella facing inward to facilitate utilization of an incision  114  having a limited length. Once the limited incision  114  has been formed, locations in the knee portion  76  of the patient&#39;s leg  70  may be inspected utilizing an optical device similar to the endoscope  352  of  FIGS. 32 and 33 . It is believed that the surgeon will bend the leg  70  of the patient between the flexed condition of  FIG. 32  and the extended condition of  FIG. 33  and will rotate the lower portion of the leg about it longitudinal central axis, in the manner indicated by the arrow  258  in  FIG. 25  prior to positioning of the implant  950  in the knee portion  76  of the leg  70 . This will enable the surgeon to detect any present or potential interference between the implant  950  and tissue in the knee portion  76  of the patient&#39;s leg  70 . 
     Once this has been done, the surgeon may or may not decide to cut tissue in the knee portion  76  of the patient&#39;s leg  70  before inserting the moveable implant  950 . If the surgeon elects to cut tissue in the knee portion  76  before insertion of the implant, this cutting will be relatively minor and will not involve the femoral and tibial cuts depicted in  FIGS. 13-23  herein. This is because the moveable implant  950  is to be positioned between surfaces  958  and  960  which are in their existing condition. Of course, eliminating the major femoral and tibial cuts illustrated in  FIGS. 13-23  herein will reduce the patient&#39;s post-operative recovery time. In addition, elimination of the major femoral and tibial cuts illustrated in  FIGS. 13-23  enables the size of the incision  114  to be reduced. 
     Once the moveable implant  950  has been positioned between the existing surfaces  958  and  960  on the femur  126  and tibia  214 , the patella  120  is moved from the offset position of  FIG. 8  back to its normal position relative to the distal end portion  124  of the femur  126  and the proximal end portion  212  of the tibia  214 . While the lower portion of the leg  70  is suspended from the upper portion of the leg and while the upper portion of the leg is held above the support surface  64  by the leg support  80  ( FIG. 2 ), the incision  114  is closed in a normal manner. Prior to closing of the incision, an imaging apparatus can be utilized to generate images of the knee portion  76  during bending of the leg  70  between the flexed and extended conditions of  FIGS. 32 and 33 . 
     Any known imaging apparatus may utilized to image the knee portion  76  of the patient&#39;s leg  70 . For example, the known C-arm fluoroscope  360  of  FIG. 34  may be utilized to generate images of the knee portion  76  of the patient&#39;s leg  70 . These images will enable the surgeon to determine the manner in which the implant  950  will move relative to the femur  126  and tibia  214  during bending of the patient&#39;s leg. Prior to closing of the incision  114 , any corrective action which the surgeon may believe is necessary can be taken to make certain that the moveable implant  950  is in the desired relationship with the femur  126  and tibia  214 . 
     Rather than forming the incision  114  in the manner illustrated schematically in  FIG. 6 , the incision may be formed with an even shorter length and a cannula, corresponding to the cannula  364  of  FIG. 39 , inserted into the incision. The implant  950  may be moved through the resiliently expandable cannula into the space between the existing surfaces  958  and  960  ( FIG. 59 ) on the femur  126  and tibia  214 . The cannula would stretch the viscoelastic material of tissues in which the very limited incision is formed to resiliently expand the extent of the incision  114  to enable the implant  950  to be moved through the incision even though the moveable implant  950  is larger than the incision. 
     The cannula  564  ( FIG. 39 ) through which the implant  950  ( FIG. 59 ) is moved into the space between the surfaces  958  and  960  is advantageously expandable to accommodate the implant  950 . The cannula may have any one of the constructions previously described in conjunction with  FIG. 39  herein. If desired, multiple incisions, corresponding to the incisions  114  and  920  of  FIG. 57  may be utilized during positioning of the implant  950 . An expandable cannula may be associated with either or both of the incisions. Fiberoptic devices, such as an endoscope or arthroscope, may be inserted through a very small corresponding to the incision  920  of  FIG. 57 , to facilitate positioning of the implant  950 . By utilizing an expandable cannula and/or arthroscopic and endoscopic surgical procedures, the size of the incision  114  through which the implant  950  is moved can be minimized. 
     The moveable implant  950  is flexible so that force transmitted between the femur  126  and tibia  214  deflects the moveable implant  950 . This results in the moveable implant  950  being shaped by the surfaces  958  and  960  on the femur  126  and tibia  214 . By shaping the upper surface  952  on the moveable implant  950  with the surface  958  on the femur  126 , smooth sliding engagement is provided between the surface  958  on the femur  126  and the upper surface  952  on the moveable implant  950 . Similarly, the lower surface  954  on the implant  950  is shaped by the surface  960  on the tibia  214 . By shaping the lower surface  954  on the implant  950  with the surface  960  on the tibia  214 , smooth sliding engagement is provided between the surface  960  on the tibia  214  and the lower surface  954  on the moveable implant  950  during bending of the knee portion  76 . 
     Shaping of the surfaces  952  and  954  on the moveable implant  950  may be accomplished in any one of many different ways. For example, the implant  950  may be formed of a material which is resiliently deflected by the surfaces  958  and  960  on the femur  126  and tibia  214 . This results in the upper surface  952  and lower surface  954  and the moveable implant  950  being resiliently deflected to have a configuration corresponding to the configuration of the portions of the surfaces  958  and  960  which are engaged by the moveable implant during bending of the knee portion  76 . During bending of the knee portion  76 , the moveable implant  950  shifts or moves relative to the surfaces  958  and  960  on the femur  126  and tibia  214 . During this shifting movement, the configuration of the upper surface  952  and the lower surface  954  of the moveable implant  950  is resiliently changed by forces transmitted between the femur  126  and tibia  214  through the moveable implant  950 . 
     Rather than having the moveable implant  950  resiliently deflected by force transmitted between the femur  126  and tibia  214 , the moveable implant  950  may be plastically deformed by the force transmitted between the femur and the tibia. Thus, the surface  958  on the femur  126  may plastically deform the upper surface  952  on the moveable implant  950  so that it retains a configuration corresponding to the configuration of the surface  958  on the femur  126 . Similarly, the surface  960  on the tibia  214  may be plastically deform the lower surface  954  on the moveable implant  950  so that it maintains a configuration corresponding to the configuration of the surface  960  on the tibia  214 . By plastically deforming the material of the moveable implant  950  with the surfaces  958  and  960  on the femur  126  and tibia  214 , smooth sliding engagement is obtained between the upper and lower surfaces  952  and  954  on the moveable implant  950  during bending of the knee portion  76 . 
     Even though the upper and lower surfaces  952  and  954  on the moveable implant  950  are either elastically or plastically shaped by the force transmitted between the femur  126  or tibia  214 , the moveable implant will, initially, be configured to have a shape corresponding to the existing space between the surfaces  958  and  960 . It is contemplated that this will result in the surfaces  952  and  954  being spaced apart by different distances between different portions of the moveable implant  950 . 
     For example, the distance between the upper surface  952  and lower surface  954  on the moveable implant  950  may be relatively large adjacent to a medial edge portion of the moveable implant  950 . The distance between the upper and lower surfaces  952  and  954  on the moveable implant  950  may be relatively small adjacent to a lateral edge portion of the moveable implant. As was previously mentioned, it is contemplated that images be generated of the knee portion  76  to enable the shape of the existing space between the surfaces  958  and  960  to be determined and to enable the moveable implant  950  to be configured, outside of the patient&#39;s body, to a configuration which generally conforms to the configuration of the space between the surfaces  958  and  960 . Once the moveable implant  950  has been initially shaped to a configuration corresponding to the configuration of the space between the surfaces  958  and  960 , the implant is positioned between the surfaces. 
     It is contemplated that the moveable implant  950  may be relatively thin compared to the thickness of the moveable implant illustrated schematically in  FIG. 59 . This would result in the upper surface  952  of the moveable implant  950  being spaced apart from the lower surface  954  of the moveable implant by a relatively small distance. By forming the moveable implant  950  with a relatively small thickness, that is, the distance between the upper surface  952  and the lower surface  954 , the implant will be relatively flexible. This enables the implant to be deflected by force transmitted between the surfaces  958  and  960  on the femur  126  and the tibia  214 . 
     It is contemplated that a relatively flexible moveable implant  950  may be configured so as to readily fit into an existing space in the knee portion  76 . This would result in a tendency for the moveable implant  950  to become seated on the proximal end portion  212  of the tibia  214 . The moveable implant  950  would be seated on the proximal end portion  212  of the tibia  214  by force applied against the moveable implant by the surface  958  on the femur  126 . The lower surface of the moveable implant would be permanently deflected to have a configuration corresponding to the configuration of the upper surface  960  in the tibia  214 . The upper surface  952  of the moveable implant would have an overall configuration which may differ from the configuration of the surface  958  on the femur  126 . However, even though the configuration of the upper surface  952  on the moveable implant  950  is different than the configuration on the surface  958  on the femur  126 , there would be smooth sliding engagement between the surface  958  on the femur  126  and the upper surface  952  of the moveable implant  950 . The result would be that there would be relatively little movement between the lower surface  954  of the moveable implant  950  and the surface  960  on the tibia  214  during bending of the knee portion  76 . However, there would be a relatively large amount of movement between the upper surface  952  of the implant  950  and the surface  958  on the femur  126 . Since the moveable implant  950  would be permanently deflected to have a configuration corresponding to the space between the existing surfaces  958  and  960  on the femur  126  and tibia  214 , the existing surfaces  958  and  960  on the femur  126  and tibia  214  would cooperate with the moveable implant  950  without inducing pain in the knee portion  76  of the leg  70  of the patient. 
     It is contemplated that the moveable implant  950  may be formed of many different materials. For example, the moveable implant  950  may be formed of a biological material. For example, the moveable implant  950  may be formed of allograft or autograft or xenograft. Combinations of these graft materials may be utilized. These graft materials may be shaped in the manner disclosed in U.S. Pat. No. 5,888,219. The moveable implant  950  may be formed of the same materials as the implant  626  of  FIGS. 43 and 45  if desired. 
     It is believed that it may be desired to form the moveable implant  950  of metal. For example, the moveable implant  950  could be formed of chromium, titanium, tantalum, zirconium or aluminum. The metal forming a moveable implant may or may not have a porous construction. The metal forming the moveable implant  950  would have a wettable surface which can be wetted by body fluids to provide lubricity. If the moveable implant  950  is formed of a porous metal, the metal may be impregnated with one or more polymeric materials which function as lubricants. 
     The moveable implant  950  may be formed of a ceramic material. The ceramic material of the moveable implant may have either a porous or non-porous construction. When the ceramic material of the moveable implant  950  has a porous construction, it is contemplated that the openings in the ceramic material will be filled with a lubricant to facilitate relative movement between the surfaces  958  and  960  on the femur  126  and tibia  214  and the surfaces  952  and  954  on the moveable implant  950 . 
     When the moveable implant  950  is formed of a porous material, for example a porous metal or a porous ceramic, it is contemplated that the moveable implant could be impregnated with both a bone growth promoting material and a lubricant. For example, the portion of the porous moveable implant  950  adjacent to the upper surface  952  of the implant may be impregnated with a lubricant. The portion of the moveable implant  950  adjacent to the lower surface  954  may be impregnated with bone growth inductive materials. 
     With such a construction, the lower surface  954  of the moveable implant is configured to correspond to the configuration of the surface  960  on the tibia  214 . Therefore, the moveable implant will tend to become seated on the proximal end portion  212  of the tibia  214 . Once this has occurred, the bone growth promoting materials in the porous implant  950 , adjacent to the lower surface  954  of the implant, will promote growth of bone into the moveable implant  950  to connect the moveable implant with the tibia  214 . The lubricant in the porous material adjacent to the upper surface  952  of the moveable implant  950  will minimize friction with the surface  958  on the femur  126  so that there will be minimal tendencies for the moveable implant  950  to move relative to the tibia  214  once the moveable implant has become seated on the proximal end portion  212  of the tibia. Of course, this will facilitate the growth of bone between the surface  960  on the proximal end portion  212  of the tibia  214  and the moveable implant  950 . 
     The moveable implant  950  may be formed of graft materials which have been shaped in the manner disclosed in U.S. Pat. No. 5,888,219. If desired, the moveable implant  950  may have a three dimensional scaffold or framework structure on which graft materials are disposed. The framework on which the graft materials are disposed may have sufficient flexibility to enable the moveable implant  950  to be flexed to correspond to the configuration of the surface  960  on the tibia  214  by force applied against the upper surface  952  of the moveable implant by the femur  126 . The graft materials on the scaffold will be shaped by the surface  958  on the femur  126  to form the upper surface  952  of the implant with the configuration which corresponds to the configuration of the surface  958  on the femur. 
     It is contemplated that the moveable implant  950  may be formed of materials which degrade with the passage of time. Thus, after the implant  950  has been disposed in the knee portion  76  of a patient&#39;s leg  70  for a predetermined period of time, for example two years, it may be necessary to replace the moveable implant  950 . Due to the limited incision required to enable the implant  950  to be positioned in the knee portion  76 , it is a relatively simple operation to replace the moveable implant  950 . The size of the incision and the trauma induced in the patient by replacing the moveable implant  950  may be minimized by the use of a cannula corresponding to the cannula  564  of  FIG. 39 . The cannula through which the implant  950  is moved into the knee portion  76  of the patient&#39;s leg may have a construction similar to the construction illustrated in U.S. Pat. Nos. 3,811,449; 5,183,464; and/or 5,961,499. 
     Seating of the moveable implant on the tibia  214  may be promoted by forming the moveable implant of a hydrophilic material which absorbs body fluids and expands. When the implant  950  of hydrophilic material is positioned in the space between the surfaces  958  and  960  on the femur  126  and tibia  214 , the hydrophilic material of the implant will absorb body fluids and expand to fully occupy the space. This will result in the lower surface  954  of the moveable implant  950  being pressed firmly against the surface  960  on the tibia  214 . Similarly, the upper surface  952  on the moveable implant  950  will be pressed against the surface  958  on the femur  126  as the moveable implant absorbs body fluids and expands. This results in the moveable implant  950  expanding in such a manner as to change the configuration of the moveable implant to the configuration of the space between the surfaces  958  and  960  on the femur  126  and tibia  214 . 
     The hydrophilic material of the moveable implant  950  may be a polymeric material which is either a copolymer or a dipolymer. The hydrophilic material may contain petroylglupamic acid, carboxymethylcellulose, a collagen or polylactide. The hydrophilic material may be a ceramic that is found in hydroxyapatite composites with polyethylene, polylactide or polyhydroxybutyrate. Of course, the moveable implant  950  could be formed of other known hydrophilic materials which attract body liquid under the influence of molecular attraction and establishes molecular linkages with the body liquid. The hydrophilic material may be disposed on a frame work or base which is formed of a non-hydrophilic material such as a porous metal. 
     It should be understood that the patient&#39;s leg  70  is supported in a manner previously explained herein in conjunction with  FIGS. 2 and 3 . The improved drape system  100  of  FIGS. 4 and 5  may be utilized during surgery in which the moveable implant  950  is positioned in the knee portion  76  of the patient&#39;s leg  70 . The patient&#39;s leg  70  may be moved in the manner schematically by arrows in  FIG. 25  to enable a surgeon to make certain that the moveable implant  950  cooperates with the femur  126  and tibia  214  in a desired manner. The articular surface  122  on the patella  120  may be repaired in the manner indicated schematically in  FIGS. 35 and 36 , contemporaneously with positioning of the moveable implant  950  in the knee portion  76 . One or more expandable devices, similar to the expandable devices  720 ,  722  and  730  of  FIGS. 51 and 52  may be utilized to facilitate positioning of the moveable implant  950  in the knee portion  76  of a patient&#39;s leg  70 . It should be understood that any of the features previously described in conjunction with  FIGS. 1-58  herein could be utilized, if desired, in association with the moveable implant  950 . 
     Moveable Inlay 
     In the embodiment of  FIG. 59 , the moveable implant  950  is positioned in engagement with existing surfaces  958  and  960  on the femur  126  and tibia  214 . In the embodiment illustrated in  FIG. 60 , a moveable implant  970  is positioned in a recess  972  formed in a medial portion of the proximal end portion  212  of the tibia  214 . The recess  972  may be relatively shallow and formed with a minimum or no cutting away of bone from the proximal end portion  212  of the tibia  214 . The recess may be formed by cutting away cartilage and/or other material disclosed on the proximal end portion  212  of the tibia  214 . Depending upon the condition of the proximal end portion  212  of the tibia  214 , the bone may or may not be cut away to form the recess  972 . Thus, the recess may be formed in tissues, such as fibrous tissues, associated with the end portion of the bone at the proximal end portion of the tibia  214 . 
     The moveable implant  970  may be held in position relative to the proximal end portion  212  of the tibia  214  by engagement with the recess  972 . If this is done, tissue growth promoting materials and/or materials which promote biological resurfacing may be provided in the moveable implant  970 . These materials would promote the growth of tissue adjacent to the proximal end portion  212  of the tibia  214  into the moveable implant  970 . The biological resurfacing materials would promote the growth of naturally occurring tissues, which were not removed to form the recess  972 , into the moveable implant  970 . Thus, cartilage tissues located adjacent to the peripheral aspect of the proximal end portion  212  of the tibia  214  would grow into the moveable implant  970 . 
     It should be understood that the recess  972  may have a lower surface formed by the existing surface  960  of the tibia and side surfaces formed by fibrocartilage which extends around the periphery of the moveable implant  970 . It is believed that it will be desired to position the moveable implant  970  in the recess  972  without anchoring the moveable implant to the tibia  214 . However, if desired, an adhesive such as fibrin could be utilized to connect the moveable implant with the existing surface  960  on the proximal end portion  212  of the tibia. The moveable implant  970  may have any one of the constructions previously described in conjunction with the implant  640  of  FIGS. 46 and 48  or the multi layered implant  670  of  FIG. 49 . 
     Multi Component Moveable Implant 
     The moveable implant  950  of  FIG. 59  is formed as one piece. In the embodiment of the invention illustrated in  FIG. 61 , the moveable implant  980  is formed with a plurality of pieces. The moveable implant  980  is disposed between a medial portion of the distal end portion  124  of a femur  126  and a medial portion of the proximal end portion  212  of a tibia  214 . The moveable implant  960  is positioned between an existing surface  958  on the femur  126  and an existing surface  960  on the tibia  214 . The moveable implant  980  includes an upper section  982  and a lower section  984 . The upper section  982  has an upper surface  988  which engages the existing surface  958  on the distal end portion  124  of the femur  126 . The upper section  982  of the moveable implant  980  has a lower surface  990  which engages the lower section  984  of the moveable implant  980 . 
     The lower section  984  of the moveable implant  980  has a lower surface  994  which engages the existing surface  960  on the proximal end portion  212  of the tibia  214 . In addition, the lower section  984  of the implant  980  has an upper surface  986  which engages a lower surface  990  on the upper section  982  of the moveable implant  980 . 
     The surfaces on the moveable implant  980  which engage existing surfaces on the femur  126  or tibia  214  are shaped to conform to the configuration of the existing surfaces on the femur and the tibia. To enable the surfaces on the moveable implant to be shaped to conform to the configuration of existing surfaces on the femur  126  and tibia  214 , images of the femur and tibia are generated utilizing known imaging apparatus, such as an MRI, X-ray, or fluoroscope. These images are utilized to determine the configuration of the existing surface  958  on the femur  126  and the existing surface  960  on the tibia  214 . The upper surface  988  on the upper section  982  of the moveable implant  980  is then shaped to a configuration corresponding to the configuration of the existing surface  958  on the femur  156 . The lower surface  994  on the lower section  984  of the moveable implant  980  is shaped to a configuration corresponding to the configuration of the existing surface  960  on the tibia  214 . By shaping the upper and lower surfaces  988  and  994  on the implant  990  to conform to the shape of the existing surfaces  958  and  960  on the femur  126  and tibia  214 , the upper and lower sections  982  and  984  tend to seat themselves on the femur  126  and tibia  214 . Thus, the upper surface  988  on the upper section  982  of the moveable implant  980  becomes seated against the existing surface  958  on the femur  126  under the influence of force transmitted between the existing surface  958  on the femur and the upper surface  988  on the upper section  982  of the moveable implant  980 . Similarly, the lower surface  994  on the lower section  984  of the implant  980  becomes seated against the existing surface  960  on the tibia  214  under the influence of force applied to the upper surface  996  on the lower section  984  of the moveable implant  980  by the upper section  982  of the moveable implant. 
     The lower surface  990  on the upper section  982  of the moveable implant  980  and the upper surface  996  on the lower section  984  of the moveable implant  980  are shaped to promote the desired articulation in the knee portion  76  of the leg  70 . Once the two sections  982  and  984  of the moveable implant  980  have been positioned between the existing surfaces  958  and  960  on the femur  126  and tibia  214 , relative movement occurs where the lower surface  990  on the upper section  982  of the moveable implant  980  engages the upper surface  996  on the lower section  984  of the moveable implant. This tends to minimize any pain or discomfort resulting from defects in the existing surfaces  958  and  960  on the femur  126  and tibia  214  during bending of the knee portion  76 . 
     The upper section  982  and lower section  984  may be formed of the same materials or any combination of the same materials as previously described in conjunction with the moveable implant  950  of  FIG. 59 . Although the upper section  982  and lower section  984  of the moveable implant  980  are fanned of the same material, it is contemplated that the upper section  982  could be formed of a material which is different than the material forming the lower section  984  of the moveable implant  980 . 
     The moveable implant  980  will be positioned in the space between the existing surfaces  958  and  960  on the femur  126  and tibia  214  in the manner previously discussed in conjunction with the embodiment of the invention illustrated in  FIG. 59 . Thus, the patient&#39;s leg will be supported in the orientation illustrated in  FIGS. 2 and 3  during the making of a limited incision along one side of the patella  120  in the manner illustrated in  FIG. 6 . The patella  120  may then be offset to one side. Alternatively, the patella may remain in its initial position or be offset just slightly to provide sufficient space to insert the moveable implant  980 . It is contemplated that the knee portion  76  will be inspected utilizing fiberoptic devices similar to the endoscope  352  of  FIGS. 32 and 33 . An expandable cannula corresponding to the cannula  364  of  FIG. 39 , may be inserted into the incision and the endoscope and/or the moveable implant  980  inserted into the knee portion  76  through the expandable cannula. 
     Moveable Implant with Anchored Section 
     In the embodiment of the invention illustrated in  FIG. 61 , the moveable implant  980  has upper and lower sections  982  and  984  which are moveable relative to each other and relative to the femur  126  and tibia  214 . In the embodiment of the invention illustrated in  FIG. 62 , a moveable implant  1002  has a section which is fixedly connected with a bone in the knee portion  76  of the patient. In the embodiment of the invention illustrated in  FIG. 62 , the moveable implant  1002  includes an upper section  1006  and a lower section  1008 . The upper section  1006  of the implant  1002  is freely moveable relative to the femur  126 . The lower section  1008  of the moveable implant  1002  is anchored to the tibia  214 . Thus, the upper section  1006  of the moveable implant  1002  is freely moveable relative to the existing surface  958  on a medial portion of the distal end portion  124  of the femur  126 . The upper section  1006  is also freely moveable relative to the tibia  214 . However, the lower section  1008  of the moveable implant  1002  is anchored to the tibia  214  by a keel or projecting section  1012 . The projecting section  1012  extends through the existing surface  960  on a medial portion of the proximal end portion  212  of the tibia  214 . 
     The upper section  1006  and lower section  1008  of the moveable implant  1002  are formed of the same material as previously discussed in conjunction with the moveable implant  950 . The upper and lower sections  1006  and  1008  of the moveable implant  1002  are positioned in the space between the existing surfaces  958  and  960  through a cannula which corresponds to the cannula  564  of  FIG. 39 . The cannula extends into a limited incision and is resiliently expandable to stretch the viscoelastic body tissue in which the limited incision is formed to enable the moveable implant  1002  to be moved through the cannula into the space between the existing surfaces  958  and  960  on the femur  126  and tibia  214 . 
     Although the lower section  1008  of the moveable implant  1002  has been illustrated in  FIG. 62  as being anchored to the tibia  214  and the upper section  1006  freely moveable relative to the femur  126 , this could be reversed if desired. Thus, the upper section  1006  of the moveable implant  1002  could be anchored to the femur  126 . If this was done, the lower section  1008  of the moveable implant  1002  would be freely moveable relative to the tibia  214 . 
     Securing Moveable Anchor 
     In the embodiment of the invention illustrated in  FIG. 59 , the moveable implant  950  is freely moveable relative to the existing surfaces  958  and  960  on the femur  126  and tibia  214 . In the embodiment of the invention illustrated in  FIG. 63 , a moveable implant  1020  is connected with the medial collateral ligament  1022 . Although the moveable implant  1020  is disposed between and is freely moveable relative to existing surfaces  958  and  960  on the femur  126  an the tibia  214 , the connection between the moveable implant  1020  and the medial collateral ligament  1022  limits the range of movement of the moveable implant  1020  relative to the existing surface  958  on a medial portion of the distal end portion  124  of the femur  126 . Similarly, the connection between the moveable implant  1020  and the medial collateral ligament  1022  limits the range of movement of the implant  1020  relative to the existing surface  960  on a medial portion of the proximal end portion  212  of the tibia  214 . 
     The moveable implant  1020  has the same construction as the moveable implant  950  of  FIG. 59 . However, the moveable implant  1020  is provided with a small passage or opening which enables a suture  1026  to be used to interconnect the moveable implant  1020  and the ligament  1022 . The suture  1026  extends through the opening in the moveable implant  1020  and extends around the ligament  1022 . The suture  1026  holds the moveable implant  1020  in engagement with the ligament  1022 . This results in a side surface  1030  on the moveable implant  1020  being held in intimate apposition with the ligament  1022 . Due to engagement of the side surface  1030  on the moveable implant  1020  with the ligament  1022 , tissue can grow from the ligament into the moveable implant  1020  to further interconnect the ligament and the movable implant. 
     It is contemplated that the moveable implant  1020  will have a construction which promotes the in growth of tissue from the ligament  1022  into the implant. Thus, the moveable implant  1020  may have a porous scaffold on which tissue growth inductive factors are disposed. For example, the moveable implant  1020  could be formed of porous tantalum. The porous tantalum scaffold could contain collagen, fibrin, progenitor cells and/or tissue inductive factors. Of course, other known materials which promote biological resurfacing could be provided on the porous metal scaffold of the moveable implant  1020  if desired. 
     Although one specific construction of the moveable implant  1020  has been described, it is contemplated that the moveable implant  1020  could have many different constructions. For example, the moveable implant  1020  could have any one of the constructions and be formed of any one or more of the materials previously described in conjunction with the moveable implant  950 . 
     It is contemplated that the patient&#39;s leg  70  may be in the position illustrated in  FIGS. 2 and 3  during positioning of the moveable implant  1020  in the space between the existing surfaces  958  and  960  on the femur  126  and tibia  214 . The upper portion of the patient&#39;s leg  70  may be supported above the support surface  64  ( FIG. 2 ) by the leg support  80 . The drapery system  100  of  FIGS. 4 and 5  may advantageously be utilized during positioning of the moveable implant  1020  to provide a sterile field. 
     Connection of Moveable Implant with Soft Tissue 
     In the embodiment of the invention illustrated in  FIG. 59 , the moveable implant  950  is freely moveable relative to the existing surfaces  958  and  960  on the femur  126  and tibia  214 . In the embodiment of the invention illustrated in  FIG. 63 , the moveable implant  1020  is connected with the ligament  1022  to limit the range of movement of the moveable implant  1020 . In the embodiment of the invention illustrated in  FIG. 64 , a moveable implant  1040  is connected with soft tissue other than the ligament  1022  of  FIG. 63 . Rather than being connected with the soft tissue by single suture  1026  in the manner illustrated in  FIG. 63 , the moveable implant  1040  is connected with soft tissue in a plurality of locations by a plurality of sutures. 
     The moveable implant  1040  ( FIG. 64 ) has the same construction as the moveable implant  950  of  FIG. 59 . The moveable implant  1040  is positioned between existing surfaces  958  and  960  ( FIG. 59 ) on a femur  126  and tibia  214  in the same manner as is illustrated schematically in  FIG. 59  for the moveable implant  950 . The moveable implant  1040  is moved into position between the existing surfaces on a femur and a tibia in the same manner as previously explained in conjunction with the moveable implant  950  of  FIG. 59 . Thus, the moveable implant  1040  of  FIG. 64  is moved into a position between existing surfaces  958  and  960  on a femur and tibia through a limited incision and a resiliently expandable cannula corresponding to the cannula  564  of  FIG. 39 . 
     In accordance with one of the features of this embodiment of the invention, a plurality of connections  1044  are provided between the periphery of the moveable implant  1040  and soft tissue  1046 . Although many different soft tissues in the knee portion  76  of a patient&#39;s leg may be connected with the moveable implant  1040  by connections  1044 , in the embodiment of the invention illustrated in  FIG. 64 , the moveable implant  1040  is connected with the joint capsule in the knee portion  76  of the patient&#39;s leg  70 . The joint capsule extends around and encloses the knee joint. Therefore, the connections  1044  can be formed between the moveable implant  1040  and the soft tissue of the joint capsule  1046  at a plurality of locations in the manner illustrated in  FIG. 64 . 
     By providing anterior and posterior connections  1044  with the soft tissue of the joint capsule  1046 , the moveable implant  1040  is held against excessive movement in either a posterior or anterior direction. Similarly, the connections  1044  between the moveable implant  1040  and the medial portion of the soft tissue or joint capsule  1046  holds the moveable implant  1040  against excessive movement in either the medial or lateral direction. The connections  1040  may initially be formed by sutures. 
     Although the range of movement of the moveable implant  1040  relative to the femur  126  and tibia  214  ( FIG. 59 ) is limited by the connections  1044  ( FIG. 64 ), the moveable implant  1040  is freely moveable relative to the existing surfaces  958  and  960  ( FIG. 59 ) on the femur  126  and tibia  214  within the range of movement established by the connections  1044  with the soft tissue or joint capsule  1046 . 
     Tissue inductive growth factors are provided on the moveable implant  1040 . The tissue inductive growth factors promote a growth of the soft tissue onto the moveable implant  1040 . It is contemplated that the moveable implant  1040  will have a porous platform in which the tissue growth inductive factors are disposed. This will promote a growth of the soft tissue or joint capsule  1046  into the moveable implant  1040  to assist the sutures at the connections  1044  in interconnecting the moveable implant  1040  and the soft tissue or joint capsule  1046 . 
     Thus, the connections  1044  between the moveable implant  1040  and the soft tissue  1046  is initially established by sutures which extend between the moveable implant  1040  and the soft tissue or joint capsule  1046 . With the passage of time, tissue grows from the soft tissue or joint capsule  1046  into the periphery of the moveable implant  1040  to further interconnect the moveable implant  1040  and the soft tissue. The sutures which initially form the connections  1044 , hold the periphery of the moveable implant  1040  in engagement with the soft tissue  1046 . Due to the intimate apposition of the moveable implant  1040  with the soft tissue or joint capsule  1046  and the tissue growth promoting factors in the moveable implant  1040 , growth of the soft tissue or joint capsule  1046  into the periphery of the moveable implant  1040  is promoted. 
     Molded Implant 
     In the embodiment of the invention illustrated in  FIGS. 65 and 66 , an implant  1060  is molded onto an existing surface  960  on the proximal end portion  212  of the tibia  214 . The implant  1060  is formed of bone cement which is held in place by a retainer or dam  1064  which extends around a medial portion of the proximal end portion  212  of the tibia  214 . The dam forms a compartment which is filled with the bone cement. As the bone cement hardens, the femur  126  ( FIG. 59 ) is moved relative to the tibia  214  to impart a desired configuration to the bone cement. 
     Once the bone cement has hardened, the retainer or dam  1064  may be removed. The bone cement then forms an implant which is disposed on the existing surface  960  of the tibia  214 . The bone cement is connected with existing surface  960  of the tibia  214  by adhesion between the implant  1060  and the existing surface  960  of the tibia  214 . It is contemplated that a releasing agent could be mixed with the bone cement which is used to form the implant  1060  so that the implant would not adhere to the existing surface  960  of the tibia  214 . This would result in the implant  1060  being freely moveable relative to both the tibia  214  and the femur  126  in the same manner as in which the moveable implant  950  is freely moveable relative to the femur  126  and tibia  214 . 
     Deformity Correction 
     The moveable implants of  FIGS. 59-66  are utilized to affect a resurfacing of joint surfaces to minimize pain resulting from defective joint surfaces. The moveable implants of  FIGS. 59-66  are not particularly effective in correcting deformities in the femur  126  and/or tibia  214 . Thus, the moveable implant  950  ( FIG. 67 ) is positioned between the femur  126  and tibia  214  to compensate for defects in the existing surfaces  958  and  960  on the femur  126  and tibia  214 . It is contemplated that other devices will have to be utilized to compensate for bone deformities. The devices which are utilized to compensate for bone deformities may be positioned in the femur  126  and/or tibia  214 . 
     The devices which compensate for bone deformities may have a construction similar to the construction of any one of the devices disclosed in U.S. Pat. No. 6,086,593. Of course, other known devices could be utilized to correct bone deformities if desired. 
     One specific device which may be utilized to correct bone deformities is a wedge member  1080  ( FIG. 67 ). The wedge member  1080  is formed of a relatively hard rigid material. The wedge member  1080  is capable of transmitting force between upper and lower portions of a bone, such as the tibia  214 . The wedge member  1080  may be hollow and have a compartment which is filled with bone growth inductive material. The wedge member may be formed of a suitable rigid material, such as tantalum or stainless steel. Alternatively, the wedge member  1080  could be formed of a biodegradable material. It is contemplated that the wedge member  1080  may be formed of human bone. 
     When the wedge member  1080  is to be positioned in the tibia  214 , a saw cut is made to form a slot at the location where the wedge member  1080  is to be installed. The saw cut and resulting slot extend only part way through the tibia  214 . The wedge member  1080  is then moved into the slot. As the wedge member is forced into the slot, the wedge member pivots an upper portion of the tibia  214  in a counter-clockwise direction (as viewed in  FIG. 67 ) relative to a lower portion of the tibia to correct a deformity in the tibia or to compensate for a deformity in the femur  126 . 
     Although the wedge member  1080  has been illustrated in  FIG. 67  as being installed in the tibia  214 , it is contemplated that the wedge member could be installed in the femur  126  if desired. Although the wedge member  1080  has been illustrated in  FIG. 67  as being installed in a medial portion of the tibia  214 , the wedge member  1080  could be installed in a posterior, anterior or lateral portion of the tibia if desired. The wedge member  1080  has the same construction and cooperates with the femur in the same manner as is disclosed in the aforementioned U.S. Pat. No. 6,086,593. 
     It is contemplated that the patient&#39;s leg  70  will be in the position illustrated in  FIGS. 2 and 3  during installation of any one of the implants illustrated in  FIGS. 59-66 . However, the implants could be positioned in the patient&#39;s leg with the patient&#39;s leg in a different orientation if desired. Thus, any one of the implants of  FIGS. 59-66  could be placed in the patient&#39;s leg with the patient&#39;s leg in either the flexed or extended orientation illustrated in  FIG. 1 . 
     The foregoing description of the moveable implants of  FIGS. 59-66  has been in conjunction with the knee portion  76  of a patient&#39;s leg  70 . However, it is contemplated that the implants will be used in association with other joints in a patient&#39;s body. For example, any one of the implants of  FIGS. 59-66  could be utilized in association with a glenoid joint. Alternatively, any one of the implants could be used in association with an ankle, wrist or elbow joint. It is contemplated that any one of the many different features of the present invention may be utilized separately or in association with the implants illustrated in  FIGS. 59-66  and that the implants may be used in association with any desired joint in a patient&#39;s body. 
     In-Situ Bone Removal 
     As previously detailed, one aspect of the present invention is the performance of all or a portion of a surgical procedure through a cannula.  FIGS. 68-74  show one embodiment of this aspect as applied to the hip joint. Access to acetabulum  1100  and proximal portion of femur  1102  may be obtained through a cannula  1104 . Cannula  1104  is inserted into incision  1106 , which is formed with a relatively short length (generally less than 10 cm in length) in the manner previously described herein. Cannula  1104  has an initial size, illustrated in  FIG. 68 , which stretches the viscoelastic tissue around the hip joint. Therefore, initial insertion of cannula  1104  into incision  1106  is effective to expand the incision. 
       FIG. 68  shows one manner in which guidance of the cannula (and any subsequent surgical implement going therethrough) to the desired location can be facilitated. A guide wire  1108  having a sharp tip is driven through femur  1102  and pinned to bone. Although guide wire  1108  is shown pinned to acetabulum  1100 , guide wire  1108  can be pinned to femur  1102 , as discussed below. Pinning guide wire  1108  to bone helps to ensure that the location of cannula  1104  remains relatively constant during the surgical procedure. 
     A pilot hole can be created through femur  1102  to help insert guide wire  1108 . Additionally, the creation of this pilot hole and/or the insertion of guide wire  1108  can be done under imaging guidance, such as fluoroscopy. Additionally, the proximal end of guide wire  1108  or cannula  1104  ( FIG. 69 ) can include an IR reflector  1109  for use with a computer surgical navigation system to monitor the location of guide wire  1108 . As is well known, IR reflector  1109  can alternatively be an electromagnetic radiation transmitter or receiver depending on the specific computer surgical navigation system. 
     Cannula  1104  is advantageously expandable to further stretch the viscoelastic tissue. Of course, expanding cannula  1104  increases the size of a passage  1110  formed by an inner side  1112  of cannula  1104 , thereby enabling a relatively large object to pass through the passage. Thus, cannula  1104  may be expanded to facilitate movement of surgical implements, such as implants and instruments through the cannula. 
     It is contemplated that expandable cannula  1104  may have many different known constructions. The illustrated cannula  1104  is formed of elastomeric material and has the same construction as disclosed in U.S. Pat. No. 6,338,730. It should be understood that cannula  1104  could have a different construction, for example, a construction similar to the constructions disclosed in U.S. Pat. No. 3,811,449 or 5,183,464. 
     Cannula  1104  can be expanded in many different ways other than under the influence of force transmitted directly to the cannula from an object moving through the cannula. Cannula  1104  may be expanded by inserting tubular members into the cannula. Alternatively, fluid pressure could be used to expand cannula  1104  in the manner disclosed in the aforementioned U.S. Pat. No. 6,338,730. 
     By utilizing expandable cannula  1104  or the expandable pneumatic retractors previously disclosed, force can be applied against opposite sides of incision  1106  to stretch the viscoelastic material disposed adjacent to opposite sides of the incision. This will result in the relatively small incision  1106  being expanded to accommodate relatively large surgical instruments and/or implants. 
     Once cannula  1104  is inserted, guide wire  1108  can be removed if desired. Alternatively, guide wire  1108  can be used to direct insertion of other surgical implements. Regardless of whether guide wire  1108  is removed, cannula  1104  can be moved or pivoted about incision  1106  so that its location can be varied. This is particularly useful, for example, if the area surrounding the surgical site needs to be accessed. 
     Although a single incision  1106  is illustrated in  FIG. 68 , it is contemplated that a plurality of incisions could be provided. Thus, a small incision may be spaced from the incision  1106  to enable a suctioning tool to be moved into the hip joint along a path which is spaced from and may be transverse to a path along which a cutting tool is moved through the incision  1106 . A second cannula, which is smaller than the cannula  1106 , may be utilized with the second incision. 
     If desired, tissue retractors and/or dissectors can be used to create space between the soft tissue and the bones of the hip joint. Prior art mechanical dissectors and retractors can be used. It is also contemplated that fluid operated retractors, expanders, and/or dissectors may be used to retract, expand or dissect body tissue. For example, retractors having a construction similar to any one of the constructions disclosed in U.S. Pat. No. 5,197,971 may be utilized to release tissue at locations spaced from incision  1106 . When tissue is to be released at locations where there is limited accessibility from incision  1106 , a device similar to any one of the devices disclosed in U.S. Pat. No. 5,295,994 may be utilized. It is believed that devices similar to those disclosed in U.S. patent application Ser. No. 09/526,949 filed Mar. 16, 2000 may be used in ways similar to those disclosed therein to move and/or release body tissue. 
     As shown in  FIG. 69 , a fluid operated device  1114  is inserted through cannula  1104  so that a bladder  1116  is placed between soft tissue  1117  and acetabulum  1100  and femur  1102 . Bladder  1116  is inflated by fluid introduced via tubing  1118  to move soft tissue  1117  relative to acetabulum  1100  and femur  1102 . Fluid operated device  1114  may be formed of biodegradable or non-biodegradable material. If bladder  1116  and tubing  1118  are formed of a biodegradable material, they need not be removed prior to closing of incision  1106 . 
     In the case of a hip replacement surgery (total or partial), a reamer is typically used to create a uniform cavity for the acetabular component and/or an oscillating blade is typically used to remove a portion of the femoral head so that the femoral component can be received in the medullary canal of the femur. In this regard, compact cutting tools, similar to those utilized for arthroscopic, endoscopic, or fiber optic assisted surgery may be at least partially moved through passage  1110  to affect in situ removal of bone. The cutting tools may have a construction similar to the construction illustrated in U.S. Pat. No. 5,540,695 or 5,609,603. Alternatively, the cutting tools may have a construction similar to the construction disclosed in published U.S. Patent Application No. 2002/0055755 A1. 
     U.S. Pat. No. 5,269,785 also discloses a tissue removal system and method that can be used with the limited incision system according to the present invention. This patent discloses a device with a flexible shaft and a controllable tip. Furthermore, the device can be single lumen or multi-lumen, with a cannula if desired. The cutting tip can be controlled via valves, pneumatics, radio control, fiberoptic control, electric wire control, cable control, or pneumatic control. Multiple movable segments or a single movable segment can provide the flexibility. Joints can be provided between rigid sections. The flexibility and controllability are particularly useful in limited incision procedures. For example, the device can be bent over a 60-90° angle, and then selectively remove osteophytes at the edge of the tissue without damaging the associated tissue. Furthermore, the option of suction provides for tissue removal and the option of irrigation minimizes heat necrosis in the limited operative space. 
     The reaming of the acetabulum can be done in a single pass with a single reamer, or a plurality of progressively larger reamers can be used. Guide wire  1108  is particularly helpful with multiple reamers since the locking of guide wire  1108  with respect to acetabulum  1100  helps ensure that each reamer is reaming about the same central axis. 
       FIGS. 70A-70B  show another embodiment of a tissue removing surgical instrument particularly useful for minimally invasive hip replacement surgeries.  FIG. 70A  shows tissue removing surgical instrument  1120  in a retracted position so that instrument  1120  can move freely within lumen  1110  of cannula  1104 . Instrument  1120  is provided with a cannulation  1122  along a shaft  1123  so that instrument  1120  can be moved along guide wire  1108 . Upon activation, distal end  1124  of instrument  1120  assumes the shape shown in  FIG. 70B . Concave underside  1126  of the cup-shaped distal end  1124  has at least one cutting surface  1128  so that rotation of instrument  1120  in conjunction with retrograde movement of instrument  1120 , i.e. movement in the direction of arrow  1130  ( FIG. 71 ), causes removal of the bone forming the head of femur  1102 . 
     Convex top side  1132  of the cup-shaped distal end  1124  has at least one cutting surface  1134  (shown in the form of gratings typical of prior art acetabular reamers) so that rotation of instrument  1120  in conjunction with antegrade movement of instrument  1120 , i.e. movement in the direction of arrow  1136  ( FIG. 72 ), causes reaming of acetabulum  1100 . Instrument  1120  can be provided with irrigation and suctioning capacities, as taught in published U.S. Patent Application No. 200210055755 A1 to minimize heat necrosis and aid in the evacuation of the removed bone. Alternatively, a separate suctioning, and if desired, irrigation device, can be used. The separate device(s) can extend through cannula  1104  or an additional cannula. 
     Activation of instrument  1120  can occur in a number of different ways. For example, rotational movement of instrument  1120  alone can cause instrument  1120  to go from the retracted ( FIG. 70A ) to the extended position ( FIG. 70B ). U.S. Pat. No. 5,445,639 teaches one such rotational mechanism. Alternatively, fluid pressure, cable means, or other similar mechanisms can be used for activation. 
     After removal of the head of femur  1102  and reaming of acetabulum  1100 , the cutting tool or tools can be withdrawn from the hip joint. In the case of instrument  1120 , instrument  1120  can be pulled back through passage  1110 , with distal end  1124  in the retracted position, or in the expanded position if the diameter of passage  1110  permits and the surgeon so desires. Alternatively, distal end  1124  can be separated from the rest of instrument  1120 , for example by cutting off and removal through a separate incision. 
     It should be noted that the reaming of acetabulum  1100  and removal of the head of femur  1102  can be done with minimal, i.e. subluxation, or no dislocation of the hip joint. As previously noted, access to the joint space can be increased by movement of cannula  1104 . Additionally, the joint space can be manipulated remotely. For example and as shown in  FIG. 68 , an elongate member  1138 , such as a Schanz screw, can be inserted through a stab wound and attached to femur  1102 . Elongate member  1138  can be used as a lever arm to increase the access to the hip joint. As a result of the reduction or elimination of dislocation, the interoperative strain on the soft tissue surrounding the hip joint is minimized. Any damage or cutting of soft tissue is also minimized. These features limit post-operative pain and lead to quicker surgical recovery. 
     The present invention also envisions insertion of some or all of the implant components through cannula  1104 . This concept will be illustrated with a description of the procedure for an acetabular component. An analogous procedure for the femoral component can be used and a procedure for use with the knee has been described above.  FIG. 73  shows the backing  1140  (typically made of a metal) of an acetabular component being inserted. Cannula  1104  is in an expanded state to accommodate the backing  1140 . Alternatively, a larger non-expandable cannula could be used. Preferably, guide wire  1108  is the same guide wire that was used for cannula  1104  and tissue removing instrument  1120 . This helps to ensure that backing  1140  is implanted at the same location that the reaming occurred. 
     Guide wire  1108  can be removed so that a standard liner or insert (typically made of polyethylene) can be used in conjunction with backing  1140 . Alternatively and as shown in  FIG. 74A , an insert  1142  having a bore  1144  can be used so that insert  1142  can slide over guide wire  1108  in a manner similar to backing  1140 .  FIG. 74B  shows another design for an insert  1146  that has a bore  1148  so that insert  1146  can slide over guide wire  1108 . One different between insert  1142  and insert  1146  is the location of bore  1144  compared to bore  1148 . Bore  1148  is placed in an area where no articulation with the ball of the femoral component occurs. As a result, the tolerances for the edges surrounding bore  1148  are not a significant concern for the generation of wear debris. Regardless of the location, the bore can be sealed, for example with an adhesive, to help contain any wear debris and minimize migration. 
     Other acetabular designs can be used. For example, the backing and liner acetabular components can be bonded together, either inside or outside of the patient. The portions may be bonded together by the application of energy in any one of many different forms, such as ultrasonic energy and heat. The present invention also envisions the application of the principles described and shown in  FIGS. 68-74  to other locations in the body. Examples include the knee, the shoulder (both the glenoid and humeral components), the joints of the hand and wrist, the joints of the foot and ankle, and the spine. With respect to the spine, suitable procedures include any procedure involving the disc space and/or the vertebra, such as fusions, pedicle screw insertions, cages, or other implants. 
     In knee replacement procedures, in situ reaming of the patella as well as the condyles of the femur and tibia can be performed. Specifically, a guide wire is placed over the condyles and reaming occurs over this guide wire using a mill or a cutting saw. The patella could be removed in a similar fashion with a retrograde reamer directed by a guide wire. As previously described, the milling/cutting tools could be used in conjunction with jigs that allow a plurality of intersecting straight cuts or a smooth arc cut. The jig can be mounted on the medial or lateral side. If desired, the cutting of the femur and tibia can be done using a limited incision approach and the implantation of the femur, tibia, and/or patella components can be done through a larger incision. 
     Lateral/Medial Approach to Knee Replacement 
     As previously discussed (see, e.g.  FIG. 54  and associated text), one aspect of the present invention includes a medial or lateral approach to joint replacement and other surgeries near a joint.  FIGS. 75-77  show one embodiment of this aspect.  FIG. 75  shows that femoral medial epicondyle  1150  is osteotomized or cut from distal end  1152  of femur  1102 . This osteotomy removes the superior attachment point of medial collateral ligament  1154  so that the joint space between femur  1102  and tibia  1156  can be pivoted open and accessed from the medial side. As an alternative, the tibial medial epicondyle  1158  could be osteotomized to separate the inferior attachment point of medial collateral ligament  1154  so that the joint space could be accessed from the medial side. Additionally, either the femoral or tibial lateral epicondyle  1160 ,  1162  could be osteotomized to separate one of the attachment points of lateral collateral ligament  1164 . Furthermore, medial collateral ligament  1154  or lateral collateral ligament  1164  can be cut without the need for removal of bone, if desired. However, as healing a bone/bone interface can be easier than healing a ligament/ligament interface, separate of the ligament through an osteotomy may be preferable. 
     In this regard,  FIG. 77  shows that femoral medial epicondyle  1150  can be reattached to distal end  1152  of femur  1102  with a screw  1166  or staple. As an alternative to screw  1166 , any method suitable for reattaching one piece of bone to another piece of bone can be used. 
     By accessing the joint space from a side medial or lateral to the centerline of the joint, the incision can be made shorter, as previously discussed. Additionally, and as previously discussed, a medial or lateral incision stretches less than a direct anterior incision. With respect to the knee joint in particular, when an incision is directly over the patella, the incision length increases 30% from 0° extension to 120° flexion. If the incision is shifted more laterally or medially, such as over the medial collateral ligament, the incision only lengthens approximately 12% from 0° extension to 120° flexion. There is less stress on the soft tissue and therefore less scarring and less postoperative pain. Also by going more medial or lateral with the incision there is less damage and less disruption of the quadriceps mechanism. Furthermore, patella  1168  tends to naturally move toward the pivot location when the joint space is hinged open from either a medial or lateral approach. The natural movement of patella  1168  allows anterior access to the joint space without the need to evert patella  1168 . However, patella  1168  can be minimally subluxed and/or everted to increase the exposure of the joint space, if desired. 
     Returning to the embodiment in  FIGS. 75-77 , any desired procedure can be performed within any joint space. Thus, the medial or lateral approach can be applied, for example, to the hip, shoulder, the joints of the hand and wrist, the joints of the foot and ankle, and the spine. However, this embodiment is particularly useful for knee joint replacement surgeries.  FIGS. 78 and 79  show one implant that can be used in this regard. In general, prior art knee prostheses for partially or totally replacing a knee joint include a femoral component for attachment to the distal end of the femur and a tibial component for attachment to the proximal end of the tibia. The tibial component typically includes a base or tray that is implanted in the tibia and an insert or meniscal plate placed on the face of the tray for articulating with the condyles of the femoral component. The tray often includes a keel or stem that inserts in the tibia to provide stability. 
     In contrast, tibial tray  1170  is a modular unit comprising a base  1172  and a keel  1174 . An inferior surface  1176  of tibial tray  1170  is substantially flat so that tibial tray  1170  can be slid into position from the lateral or medial side onto previously cut or milled tibia  1156 . A side cutting jig analogous to that shown in  FIG. 54  or other side cutting or milling techniques can advantageously be used to prepare tibia  1156  for receiving tibial tray  1170 . Tibial tray  1170  is provided with openings  1178  that extend from a superior surface  1180  through inferior surface  1176 . Openings  1178  are sized to receive keel  1174 . As shown, keel  1174  is implanted prior to implantation of tibial tray  1170 . In another embodiment, tibial tray  1170  is implanted prior to implantation of keel  1174 . In this embodiment, openings  1178  are sized so that once tibial tray  1170  is sitting on the tibial surface, keel  1174  can be pushed or pounded through opening  1178  to secure tibial tray  1170  to tibia  1156 . 
     Base  1172  and keel  1174  can be provided with a locking mechanism to secure keel  1174  to base  1172 . One example of such a mechanism is a locking screw  1181  that inserts through base  1172  and keel  1174 . If keel  1174  is implanted after tibial tray  1170 , keel  1174  can also be provided with a head  1182  or other stop mechanism that prevents further insertion of keel  1174  through openings  1178  once keel  1174  has been inserted through openings  1178  a given distance. In one embodiment, head  1182  can be made to be flush with superior surface  1180  of base  1172 . In this regard, openings  1178  have a countersink  1184  for accommodating keel head  1182 . In another embodiment, head  1182  extends above superior surface  1180  even after full insertion through openings  1178  (i.e. stands proud with respect to superior surface  1180 ). In this embodiment, keel head  1182  can cooperate with a bore or slit provided on the inferior surface of a tibial insert to serve as a centering mechanism for insertion (locking the tibial insert to base  1172  in a fixed bearing design) and/or articulation of the femoral and tibial components (in a mobile bearing design). 
     If tibial tray  1170  were an integral single-piece unit, it would be difficult to insert tibial tray  1170  through a minimal incision, regardless of the location of the incision. However, since tibial tray  1170  is modular, base  1172  can be readily slid in through either a lateral or medial side incision (which can be smaller than typical mid-line incisions) and, keel  1174  can be interoperatively coupled to base  1172  after base  1172  is in the desired position. Keel  1174  can be inserted through the same incision as base  1172  or through a separate incision. This separate incision can be a substantially anterior incision or an incision located on the same or opposite side as the incision for base  1172 . As is well known, tibial tray  1170  can be inserted either with or without bone cement. If bone cement is used, the cement can be placed under base  1172  after it is positioned on tibia  1156  and then keel  1174  is inserted into openings  1178 . 
       FIG. 80  shows another embodiment of a tibial tray  1186  that can be used with or without a keel. An inferior surface  1188  of tibial tray  1186  includes a slot  1190  extending substantially across the entire width of inferior surface  1188 . Slot  1190  provides stability for tray  1186 . Like tray  1170 , tray  1186  can be inserted from either the medial or lateral side. Slot  1190  and/or tibial tray  1186  can be provided with a bore  1192  (or a plurality of bores) for receiving a screw  1194  or other fastener to further secure tray  1186  to the tibia. 
     Tibial tray  1186  also includes another feature to assist implantation. Specifically, like prior art tibial trays, tibial tray  1186  includes a rim  1191  for retaining the tibial insert or bearing surface. However, as shown, rim  1191  does not extend around the entire perimeter of tibial tray  1186 . Specifically, lateral and medial posterior regions  1193  have no rim. A centrally located section  1195  can be provided with a rim for retention of the tibial insert. The elimination of rim  1191  from posterior regions  1193 , facilitates implantation of the femoral component as there is no posterior rim in lateral an medial regions  1193  to impede impaction of the femoral component. Section  1195  will not interfere with impaction of the femoral component as the femoral component has a geometry matching the natural condyles of the femur. The novel feature of eliminating the posterior rim can be applied to different tibial tray designs and is not limited to tibial tray  1186 . 
     In order to facilitate implantation of tray  1186 , a side cutting or milling jig  1196  ( FIG. 81 ) can be provided with a groove  1198  having a shape that mates with slot  1190 . Thus, when tibia  1156  is cut or milled, the tibia has a recess corresponding to the shape of slot  1190 , thereby allowing tray  1186  to be readily moved into position. It should be noted that use of a jig having a groove is not necessary for implantation of tray  1186 . For example, tray  1186  can be press fit into position, either by tapping in tray  1186  in a direction along the longitudinal axis of slot  1190  or by tapping tray  1186  from the superior direction. It should also be noted that although slot  1190  is shown having a substantially dove-tail shape, slot  1190  can be made to have any suitable shape that provides stability for tray  1186 . 
       FIG. 82  shows another embodiment of a tibial tray  1200  that has a novel keel design. A keel  1202  extends from an inferior surface  1204  of tibial base  1206 . A superior surface  1208  is generically shown, and, as is well known, is configured and dimensioned for receiving an insert (not shown) that articulates against a femoral component (also not shown). Tibial base  1206  has lateral and medial regions  1210 ,  1212 . 
     When viewed from the anterior ( FIG. 82 ) or posterior direction, keel  1202  extends downward from inferior surface  1204  at an acute angle α. Thus, keel  1202  extends downward toward lateral region  1210  and away from medial region  1212 . This is in contrast to prior art keels, which generally extend substantially perpendicularly and symmetrically from the tibial base. Like prior art keels, keel  1202  can be tapered and can be inclined either posteriorly or anteriorly when viewed from the medial/lateral direction. Although keel  1202  is shown as connected to inferior surface  1204  centrally located with respect to both lateral and medial regions  1210 ,  1212 , keel  1202  can be offset with respect to either lateral or medial regions  1210 ,  1212 . 
       FIGS. 83 and 84  show examples of surgical approaches for which tibial tray  1200  is particularly useful. Specifically, knee joint space  1214  is accessed using a lateral approach such as the procedure previously described in connection with  FIGS. 75-77 . Since joint space  1214  is hinged or pivoted open from a lateral aspect  1216  about a medial aspect  1218 , the area of joint space  1214  that is accessible decreases from lateral aspect  1216  to medial aspect  1218 . As a result, it would be difficult to insert a typical tibial tray since the length of the keel (compared to the working space of medial aspect  1216 ) would not permit proper implantation. 
       FIG. 83  shows one method of implanting tibial tray  1200 . Because of the size and geometry of keel  1202 , tibial tray  1200  can be inserted into joint space  1214  at an angle β (defined by the cut surface of tibia  1156  and superior surface  1208  of tibial tray  1200 ). At angle β, lateral region  1210  is at the same height as medial region  1212  so that when tibial tray  1200  is initially inserted, inferior surface  1204  of medial region  1212  is in contact (or close to contact) with tibia  1156 . Thus, in order to implant tibial tray  1200  in tibia  1156 , lateral region  1210  is driven in tibia  1156 , with essentially rotation about medial region  1212  occurring. 
       FIG. 84  shows another method of implanting tibial tray  1200 . Here, superior surface  1208  of tibial tray  1200  is substantially parallel to the cut surface of tibia  1156 . As a result, the distal end of keel  1202  is substantially perpendicular to the cut surface of tibia  1156 . This initial substantially perpendicular relationship facilitates insertion of keel  1202  into tibia  1156 . Regardless of the method of implantation, keel  1202  can have a length so that keel  1202  does not penetrate the lateral cortex of tibia  1156  when fully inserted into tibia  1156 . 
     Although tibial trays  1170 ,  1186 , and  1200  are, as the name implies, intended for use in the tibia, the concepts can be applied to the other components in partial or total knee replacement surgeries. For example,  FIG. 85  shows a patellar implant  1220  having a slot  1222  that engages bone. Thus, patellar implant  1220  is analogous to tibial tray  1186 . Typically, patellar implants have one or more pegs that must be driven into bone. This requires substantial working space, so that the patella needs to be everted or dislocated. In contrast, patellar implant  1220  can be slid into position without evertion and with little or no dislocation. If desired, patellar implant  1220  can be fixed into position with bone cement. 
       FIG. 86  shows a femoral component  1224  that is also analogous to tibial tray  1186 . In particular, femoral component  1224  has a pair of spaced condyle sections  1226  defining curved condyle surfaces  1228 . Joining region  1230  is anterior located and connects the two condyle sections  1226 . Instead of having pins for insertion into the femur, femoral component  1224  is provided with a slot  1232  for securing femoral component  1224  to the femur. Since the pins are absent, femoral component  1224  can be slid into position from the lateral or medial side. As an alternative to slot  1232  (or in addition to slot  1232 ), each of condyle sections  1226  can be provided with an aperture for receiving a fastener to secure femoral component  1224  to the femur. This design could be analogous to tibial tray  1170 . 
     In order to facilitate insertion of femoral component  1224  through a minimally invasive lateral or medial incision, femoral component  1224  can be made modular. This allows femoral component  1224  to be implanted in sections through an incision that would otherwise be much longer which are then coupled in vivo. As shown, femoral component  1224  comprises an anterior femoral section  1234 , and a posterior femoral section  1236 . However, any desired number of sections could be used. Anterior femoral section  1234  is coupled to posterior femoral section  1236 . 
       FIG. 87  shows one manner of coupling the sections. A tongue  1238  located on one section (shown as anterior femoral section  1234 ) mates with a groove  1240  on an adjacent section (shown as posterior femoral section  1236 ). The mating results in substantially smooth condyle surfaces  1228  so as to minimize the potential for generation of wear debris. 
     Self-Centering Mobile Bearing Implant 
       FIGS. 88 and 89  show one embodiment of a self-centering mobile bearing implant according to the present invention. An implant  1250 , in the form of a prosthetic knee, comprises a femoral component  1252  secured to femur  1102  and a tibial component  1254  secured to tibia  1156 . Femoral component  1252  includes a pair of spaced apart condyle sections  1256  defining curved condyle surfaces  1258 . A joining region  1260  is anterior located and connects the two condyle sections  1256  so that a recess  1262  is defined by condyle sections  1256  and joining region  1260 . The side of femoral component  1252  facing femur  1102  can include fixation pins  1264 . As femoral component  1252  has a structure and function analogous to prior art femoral components, further description is not believed necessary. 
     Tibial component  1254  includes a tray  1266  and a bearing insert  1268 . Tray  1266  is defined by a tapered keel or spike  1270  and a plate member  1272 . As previously discussed with respect to other embodiments, other mechanisms for fixing tibial component  1254  can be used as an alternative to spike  1270 . Plate member  1272  has a superior surface  1274  defined by a concave, spherically shaped plateau surface. 
     As is more fully described below, bearing insert  1268  also has a spherically shaped surface so that the interface between tibial tray  1266  and bearing insert  1268  is defined by cooperating spherically shaped, concave and convex surfaces that enable sliding motions along these surfaces. In this regard, superior surface  1274  has a mirror polish to minimize friction during relative slidable movements of bearing insert  1268 . Additionally, superior surface  1274  is provided with a track  1276  that cooperates with a groove located on bearing insert  1268  so that the sliding motion occurs substantially in the anterior-posterior direction. Although a single track  1276  is shown centrally located, track  1276  can be located elsewhere along superior surface  1274  and/or more than one track can be used (e.g. two lateral symmetrically placed tracks). Also, the arrangement of the track and groove can be switched so that bearing insert  1268  is provided with the track and superior surface  1274  is provided with the groove. 
     Bearing insert  1268  has a superior surface  1278  that includes a pair of spaced apart curved depressions  1280  that form bearing surfaces for condyle surfaces  1258  of femoral component  1252 . Condyle surfaces  1258  and depressions  1280  are shaped so that pivoting motion between femoral component  1252  and bearing insert  1268  can occur over a wide range of motion. A protrusion  1282  can be located between depressions  1280  so that extension of protrusion  1282  into recess  1262  of femoral component  1252  substantially prevents hyperextension (counterclockwise rotation beyond a certain point) of femoral component  1252 . Interference between protrusion  1282  and recess  1262  also prevents relative motion in the lateral-medial direction. 
     Bearing insert  1268  has an inferior surface  1284  that is convex and spherically shaped and mates with concave superior surface  1274  of tibial tray  1266 . A groove  1286  is located on inferior surface  1284  and is configured and dimensioned to receive track  1276 . 
     As is evident from the foregoing, implant  1250  operates like prior art mobile bearing knee implants in the occurrence of sliding motion between bearing insert  1268  and both femoral and tibial tray  1266  components  1252 . However, unlike prior art mobile bearing knee implants that rely on tracks and grooves to substantially limit the movement to the anterior-posterior direction, the articulating surfaces are not flat. Rather, superior surface  1274  of tibial tray  1266  and inferior surface  1284  of bearing insert  1268  are mating curved surfaces. 
     With the prior art flat surfaces, there is increased risk for dislocation and variable degrees of laxity. Additionally, ligament balancing and self-centering of the joint may be more difficult, allowing for some feelings of instability and/or ligamentous laxity. Because superior surface  1274  of tibial tray  1266  and inferior surface  1284  of bearing insert  1268  are mating curved surfaces, the curvature toward the center of the tibia encourages bearing insert  1268  to want to fall back into the center of the curvature of superior surface  1274 . 
     In order to enhance ligament stability, tray  1266  and/or bearing insert  1268  can be made to have a thickness that increases from the center toward the edge. As shown in  FIGS. 88 and 89 , this increase in thickness can occur in both the anterior-posterior direction and the medial-lateral direction. Thus, as bearing insert  1268  slides, both the curvature and decrease in thickness cooperate as a self-centering mechanism that draws bearing insert  1268  back to the center of the tibia (also resisting posterior rollback), the lowest point in tibial tray  1266  when they are at rest. This enhances stability, yet allows free motion and a mobile bearing construct. 
     The curvature of inferior surface  1284  of bearing insert  1268  can be made to match the curvature of superior surface  1274  of tibial tray  1266 . Alternatively, the curvatures can be different. For example, the curvature of inferior surface  1284  can be smaller than the curvature of superior surface  1274 . Regardless of whether of curvatures match, the curvature of inferior surface  1284  and/or superior surface  1274  can be constant or have a radius which progressively varies. 
     Each of femoral component  1252 , tibial tray  1266 , and bearing insert  1268  can be made of any suitable biocompatible material. For example, femoral component  1252  and tibial tray  1266  can both be made of a metallic material such as a cobalt-chromium alloy or titanium alloy, and bearing insert  1268  can be made of a polymer such as UHMW polyethylene. This provides metal articulating against a polymer. Additionally and as previously discussed with respect to other embodiments, this can be reversed so that femoral component  1252  and tibial tray  1266  are made of a polymer and bearing insert  1268  is made of a metallic material. 
       FIG. 90  shows another embodiment of the self-centering mechanism according to the present invention. An implant  1290  in the form of a rotating platform knee implant includes a tibial component  1292  secured to the tibia and a femoral component secured to the femur. As the femoral component used with implant  1290  is analogous to femoral component  1252 , reference is made to  FIGS. 88 and 89  and accompanying text and further description is not believed necessary. 
     Tibial component  1292  includes a tray  1294  and a bearing insert  1296 . Tray  1294  includes a tapered spike  1298  and a plate member  1300 . As was the case for tibial component  1254 , other mechanisms for fixing tibial component  1292  can be used as an alternative to spike  1298 . Plate member  1300  has a superior surface  1302  defined by a concave, spherically shaped plateau surface. 
     Analogous to bearing insert  1268 , bearing insert  1296  also has a spherically shaped inferior surface  1304  so that the interface between tibial tray  1294  and bearing insert  1296  is defined by cooperating spherically shaped, concave and convex surfaces that enable sliding motions along these surfaces. In this regard, superior surface  1302  has a mirror polish to minimize friction during relative slidable movements of bearing insert  1296 . Additionally, superior surface  1302  is provided with a post  1306  that cooperates with a recess  1308  located on bearing insert  1296  to permit rotation of bearing insert  1296  with respect to tibial tray  1294 . The arrangement of the post and recess can be switched so that bearing insert  1296  is provided with the post and superior surface  1302  is provided with the recess. 
     As is evident from the foregoing, implant  1290  operates like prior art mobile bearing knee implants in the occurrence of rotation motion between bearing insert  1296  and both femoral and tibial tray components  1292 . However, unlike prior art mobile bearing knee implants that rely on a post mechanism to control the rotational movement, the articulating surfaces are not flat. Rather, superior surface  1302  of tibial tray  1294  and inferior surface  1304  of bearing insert  1296  are mating curved surfaces. 
     Compared to the prior art, implant  1290 , like implant  1250 , provides improved dislocation risk, ligament balancing, and ligament stability. In order to enhance ligament stability, tray  1294  and/or bearing insert  1296  can be made to have a thickness that increases from the center toward the edge. Thus, as bearing insert  1296  slides, both the curvature and decrease in thickness cooperate as a self-centering mechanism that draws bearing insert  1296  back to the center of post  1306  (also resisting posterior rollback), the lowest point in tibial tray  1294  when they are at rest. This enhances stability, yet allows free motion and a mobile bearing construct. 
     As is evident from  FIG. 90 , post  1306  is not located directly over spike  1298 , i.e. the center of the tibia. Rather, post  1306  is offset medially toward the medial compartment of the knee. In prior art rotating platform designs, the post is substantially in line with the central keel. This design does not account for the anatomical motion of the knee, which has more motion and a greater range of motion laterally with greater anteroposterior translation laterally and less anteroposterior translation medially. Offsetting post  1306  more toward the medial compartment of the knee recreates the natural pivoting motion on the knee, with less translation medially, a more stable joint medially, and more rotational arc or more movement laterally. 
     Any of the above-described embodiments of self-centering mechanism can be applied to total or partial knee replacement. These embodiments could be used in any joint, such as the shoulder, ankle, wrist, as well as others. 
     Bicompartment Implants 
     As previously discussed (see, e.g.  FIG. 40  and associated text), the present invention includes implants that have interconnectable portions. Another embodiment of this concept is the combination of limited incision unicompartmental knee replacement with limited incision patellofemoral replacement. This combination can be done percutaneously with limited incisions, possibly one or two smaller incisions to approach the medial aspect of the knee in the patellofemoral joint. 
     Arthritis typically does not involve the entire joint space. Most arthritis of the knee is medial joint, lateral joint, patellofemoral joint, or some combination of two of these three joint compartments. Usually advanced arthritis involves both the medial or lateral compartment and the patellofemoral joint. Replacement of the medial or lateral compartment through limited incision surgery and then patellofemoral replacement through the same incision or another incision will lead to faster patient rehabilitation. Additionally, limited incision replacement of these compartments that avoided everting the patellofemoral joint and reduced damage of the quadriceps mechanism would further accelerate rehabilitation. 
       FIG. 91  shows a bicompartment arrangement that includes trochlear implant  1310  and medial implant  1312 . Implants  1310  and  1312  are dimensioned and configured so that bone  1314  is located between the implants.  FIG. 92  shows an embodiment of a bicompartment implant  1316  that includes trochlear section  1320  and medial section  1322 . In implant  1316 , there is no bone between the sections. Implant  1316  can be made so that sections  1320  and  1322  are integral. Alternatively, implant  1316  could be modular, being assembled inside the body or outside of the body prior to implantation. 
     In the interest of brevity, the reader is referred to  FIG. 40  and associated text for different methods for coupling sections  1320  and  1322 . As previously discussed, the patella and the other portions of the joint can be resurfaced to receive the implant. In this regard, the resurfacing can be with a mill, saw or robotic arm and computer navigation system. The computer navigation system could also be used to assist in aligning the unicompartmental replacement with the patellofemoral joint replacement. The patellofemoral replacement could be performed from a mid-vastus or sub-vastus approach without disrupting the quadriceps mechanism. As also previously discussed, the patella could be elevated using fluid retractors or simple mechanical retractors to minimize soft tissue damage associated with dislocating or everting the patella. 
       FIG. 92  shows the tibial component  1324 , which articulates against medial section  1322 . Each of the components can be made of any suitable biocompatible material. For example, all of the components can be made of a metallic material such as a cobalt-chromium alloy or titanium alloy. This provides metal articulating against metal. Alternative articulating surface pairs include metal/polymer, metal/ceramic, metal/composite, polymer/ceramic, polymer/polymer, polymer/composite, ceramic/ceramic, and ceramic/composite. 
     In order to reduce the generation of wear debris, the articulating surfaces can be magnetically charged to have the same polarity so that the surfaces are repelled from each other. Thus, the surfaces glide smoothly over each other, essentially floating with respect to one another. This would also potentially allow a replacement surface that is a strip or point contact, rather than being a full surface that matches the surface of the joint. This embodiment, which is described in more detail below, would include strips that glide along each other, as opposed to a full resurfacing of the joint so one would have strips in contact with each other rather than a full surface. The surface magnetic charges can diminish with time. Additionally, certain environments could also diminish the magnetic charges. For example, exposure to an MRI apparatus could severely alter the magnetic fields. In order to account for these possibilities, the magnetic charges of the articulating surfaces can be re-magnetized. 
     The present invention also envisions the application of magnetically charged articulating surfaces to other implant designs and to other locations in the body. Examples include the knee, the shoulder (both the glenoid and humeral components), the joints of the hand and wrist, the joints of the foot and ankle, and the spine. With respect to the spine, suitable procedures include any procedure involving the disc space and/or the vertebra. 
     Adjustable Cutting Jig 
     As previously discussed, various embodiments of the present invention involve a lateral or medial approach to accessing a joint space.  FIG. 93  shows an adjustable cutting jig  1330  that is particularly useful in such an approach. With the cutting jig  1330 , the femoral cuts can be made by moving a saw blade or other cutting device, such as a miller, between opposite sides of the femur in a direction extending generally perpendicular to a longitudinal central axis of the femur. Thus, the cutting device is moved along a path which extends between lateral and medial surfaces on the distal end portion  1332  of the femur  1334 . 
     The cutting jig  1330  is illustrated in  FIG. 93  as being used on a lateral surface  1336  of the femur  1334 . However, the cutting jig  1330  could be used on the medial surface of the femur  1334  if desired. When the cutting jig  1330  is mounted on the lateral surface  1336  of the femur  1334 , the incision  114  ( FIG. 6 ) is laterally offset. Similarly, when the cutting jig  1330  is mounted on a medial surface of the femur  1334 , the incision  114  is medially offset. 
     Although either intramedullary or extramedullary instrumentation can be used to attach the cutting jig  1330  to the femur  1334 ,  FIG. 93  shows intramedullary instrumentation. Accordingly, the cutting jig  1330  includes a shaft  1338  that can be inserted into the medullary canal of femur  1334  in any known manner, for example using a technique analogous to that previously described in connection with  FIGS. 8-10 . In this regard, a separate stab wound incision can be made for shaft  1338 , rather than attempting to stretch the incision  114 . 
     A length adjustment member  1340  slides along shaft  1338  so that the location of length adjustment member  1340  on shaft  1338  can be changed to accommodate different anatomies. Tightening knob  1342  can be used to lock length adjustment member  1340  at the desired location. Length adjustment member  1340  can also freely rotate about shaft axis  1344 . This is useful, for example, if a medial approach is to be used. 
     An arm  1346  extends from length adjustment member  1340 . Arm  1346  includes a head  1348  that is received in ring  1350  on length adjustment member  1340 . The arm  1346  can be made as two telescoping rods or a similar configuration so that the length of the arm  1346  can be adjusted. The head  1348  can rotate within the ring  1350  to allow rotation of the arm  1346 . A tightening knob  1352  locks the arm  1346  at the desired position. 
     An extension  1354  extends from the lateral end of arm  1346 . Like the arm  1346 , extension  1354  can be made as two telescoping rods or a similar configuration so that the length of the extension  1354  can be adjusted. A link  1356  is generically shown to indicate that different types of joints can be used to couple the arm  1346  and the extension  1354 . For example, it may be desirable to have the extension  1354  rotate and/or pivot with respect to the arm  1346 . Regardless of the specific design of the link  1356 , a tightening knob  1358  is provided to lock the extension  1354  at the desired position. 
     A cutting guide  1360  is located on an end of the extension  1354 . As was the case for link  1356 , different types of joints can be used to couple the cutting guide  1360  to the extension  1354 . The cutting guide  1360  includes a distal guide surface  1362 , an anterior chamfer guide surface  1364 , a posterior chamfer guide surface  1366 , an anterior guide surface  1368 , and a posterior guide surface  1370 . As is readily apparent, the cutting guide  1360  has a structure substantially similar to the cutting guide  800 . Furthermore, the operation and use of the cutting guide  1360  is substantially similar to that of the cutting guide  800 . Accordingly, reference is made thereto. 
     Each of the guide surfaces  1362 ,  1364 ,  1366 ,  1368 , and  1370  can be made to have a length less than the extent of the cut to be formed on the distal end portion  1332  of the femur  1334 . Therefore, after an initial portion of the cut has been made utilizing the appropriate guide surface to guide movement of the cutting tool, the cut surfaces are utilized to guide movement of the cutting tool during completion of the cut. The cutting guide  1360  is not of the capture type. Therefore, the cutting tool is free to move past the guide surfaces  1362 ,  1364 ,  1366 ,  1368 , and  1370  during completion of the femoral cuts. If the guide surfaces  1362 ,  1364 ,  1366 ,  1368 , and  1370  were formed by slots, the cutting guide  1360  could be disconnected from the femur  1334  to complete the femoral cuts. 
     The cutting guide  1360  can be made so that one or more of the guide surfaces  1362 ,  1364 ,  1366 ,  1368 , and  1370  have an adjustable length so that the size of the guided portion of the cuts can be adjusted depending upon the size of the bone and the implant that is to be used. Furthermore, the cutting guide  1360  is shown having a plurality of guide surfaces  1362 ,  1364 ,  1366 ,  1368 , and  1370 , with each guide surface being used to make a different cut. Other embodiments of cutting guides  1360  can be used with the cutting jig  1330 . 
     For example,  FIG. 94  shows a cutting guide  1372  that has a single guide surface  1374 . As will be discussed, the guide surface  1374  is movable to make multiple guided cuts of different orientations. As the cutting guide  1372  only has one guide surface  1374 , the cutting guide  1372  can be used through a smaller incision than prior art cutting blocks. The cutting guide  1372  includes a base  1376  that can be positioned on the femur using the adjustable cutting jig  1330 . In other words, the cutting guide  1372  would be a substitute for the cutting guide  1360 . Other intramedullary instrument could be used with the cutting guide  1372 . Additionally, extramedullary instrument could be employed. If desired, the base  1376  could be pinned directly to the femur in a manner analogous to the cutting guide  800  ( FIG. 54 ). Alternatively, the base  1376  could be positioned on the femur using a computer navigation system. 
     The base  1376  has a plurality of tracks  1378 ,  1380 ,  1382 ,  1384 , and  1386 . The guide surface  1374  is attached to a pin member  1388 . The pin member  1388  is sized to be received in the tracks  1378 ,  1380 ,  1382 ,  1384 , and  1386 . When pin member  1388  is located in the track  1378 , the guide surface  1374  is positioned on the femur for making an anterior cut, as shown in  FIG. 94 . When pin member  1388  is located in the track  1380 , the guide surface  1374  is positioned on the femur for making an anterior chamfer cut, as shown in  FIG. 95 . When pin member  1388  is located in the track  1382 , the guide surface  1374  is positioned on the femur for making a distal cut. When pin member  1388  is located in the track  1384 , the guide surface  1374  is positioned on the femur for making a posterior chamfer cut. When pin member  1388  is located in the track  1386 , the guide surface  1374  is positioned on the femur for making a posterior cut. 
     The pin member  1388  can be locked in the tracks  1378 ,  1380 ,  1382 ,  1384 , and  1386  to stabilize the guide surface  1374  during making of the cuts. This can be done in any number of ways. For example, the pin member  1388  can have a threaded portion that receives a nut to secure the pin member  1388  within the track. The specific configuration of the tracks  1378 ,  1380 ,  1382 ,  1384 , and  1386  shown in  FIGS. 94 and 95  are exemplary only, as any configuration that allows movement of the guide surface  1374  with respect to the base  1376  could be used. 
     As was the case with the cutting guide  1360 , the guide surface  1374  can be made so that the size of the guided portion of the cuts can be adjusted depending upon the size of the bone and the implant that is to be used. Furthermore, the guide surface  1374  can be made to have a length less than the extent of the cut to be formed on the distal end portion of the femur. Therefore, after initial portions of the cuts have been made utilizing the guide surface  1374  to guide movement of the cutting tool, the cut surfaces are utilized to guide movement of the cutting tool during completion of the cut. The cutting guide  1372  is not of the capture type. Therefore, the cutting tool is free to move past the guide surface  1374  during completion of the femoral cuts. If the guide surface  1374  were of the capture type (having a slot), the cutting guide  1372  could be disconnected from the femur to complete the femoral cuts. 
     The cutting guide  1372  is illustrated in  FIGS. 94 and 95  for use on a lateral surface of the femur. However, the cutting guide  1372  could be used on the medial surface of the femur by either flipping or rotating the base  1376 . In this regard,  FIG. 96  shows a cutting guide  1390  that could be used on either the lateral or medial side of the femur. In addition to containing the tracks  1378 ,  1380 ,  1382 ,  1384 , and  1386 , a base  1392  includes tracks  1394 ,  1396 , and  1398 . As shown, the track  1396  would be used to make a distal femoral cut on the medial side of the femur. 
     Implants with Reduced Articulating Surfaces 
     As previously detailed, the present invention relates to methods, implants, and instrumentation for performing surgery through minimally invasive procedures. One aspect is the insertion of a partial or total joint replacement implant through a minimally invasive incision. For example, modular implants that are assembled after insertion in the body can typically be more easily inserted through a smaller incision than a unitary implant of the same size or a modular implant that is assembled prior to implantation. Thus, it is advantageous to have smaller implants, modular or not, in order to reduce the size of the incision that is needed for implantation. 
     Smaller implants will generally have a smaller articulating surface area. While prior art prosthetic components provide a low-friction articulating surface for the surface of accompanying member, interaction between the articulating component and the member can produce wear debris. Such debris may cause adverse local and systemic reactions in the body. Thus, it is advantageous to minimize the articulating surface area of one or both of a joint component. 
       FIG. 97  shows one embodiment of a joint component implant  1400  that is both small in size to facilitate implantation through a minimal incision and has a reduced articulating surface area. Specifically, implant  1400  comprises a head  1402  connected to a body  1404 . In use, head  1402  articulates against the other joint component. In this regard, the other component could be an artificial component or a natural component. For example, if implant  1400  were implanted in the acetabulum  1102  as shown in  FIG. 98 , the other joint component  1403  could be the natural femoral head or the head of a prosthetic femoral component. Although head  1402  is shown as substantially spherical, any shape that provides a smooth bearing surface could be used. 
     Body  1404  includes a threaded region  1406  for fixing implant  1400  to tissue. A joining region  1408  is located between head  1402  and threaded region  1406 . Joining region  1408  is provided with multiple surfaces so that an inserter or other tool can be used to thread implant  1400  into tissue. By providing an area separate from head  1402  that is used for insertion, the risk of scratching or otherwise damaging the bearing surface is reduced. 
     Threaded region  1406  can be eliminated and other mechanisms for attaching implant  1400  can be used. For example, implant  1400  could simply be driven into the tissue. Bone cement or an adhesive could be used to attach implant  1400 . Alternatively, body  1404  could have a rivet type means, an expandable portion, or some other known fixation means. 
     Implant  1400  can be made from any biocompatible material that will undergo articulating movement with a corresponding natural or prosthetic member. For example, the bearing component could be formed from a variety of metals, polymers, ceramics, or composite materials. In the event that polymers are chosen, a high density polyethylene may be used, although numerous types of polymers may be suitable so long as the material provides both strength and a low-friction articulation surface for the corresponding joint face. If desired, head  1402  and body  1404  can be made of different materials. It may also be advantageous to include some type of known tissue in-growth promoting features on at least a portion of body  1404 . Such features include a porous or textured surface, a porous body (for example so-called “foam metals”), and osteoinductive or osteoconductive materials or factors. 
       FIG. 98  shows a number of implants  1400  located in the acetabulum  1102  for articulation against femoral head  1403 . As shown, implants  1400  can be implanted through cannula  1104  and can be cannulated so that they can be inserted over guide wire  1108 , without the need to dislocate the joint or with only slight dislocation. Implants  1400  also present a small surface area against which femoral component  1403  articulates. The bearing surface minimizes available surface area of articulation for the component and the production of wear debris. If desired, implants  1400  can be used without the need to ream acetabulum  1102 , thereby saving bone stock. Alternatively, acetabulum could be partially reamed to ensure a surface free of asperities. Because of the overall reduction in size and bearing surface of implants  1400 , a larger femoral component  1403  can be used without the risk of significant increase of wear debris. The larger femoral component  1403  may enhance joint stability. 
     Although any number of implants  1400  can be used for a given application, the use of three implants  1400  for acetabulum  1102  may be preferable as three implants serve as a centering mechanism for femoral component  1403 . In this regard, the number and location of implants  1400  can be selected to suit a particular application. The size of implants  1400 , and in particular head  1402 , can also be varied. In acetabulum  1102 , smaller heads 3-6 mm in diameter or larger heads 10-15 mm in diameter may be desirable. 
     Although  FIG. 98  shows implants  1400  used in acetabulum  1102 , implants  1400  could be used in any joint component including, a glenoid, patellar, femoral, humoral, tibial, ulnar, radial, wrist, and/or ankle component for a prosthetic joint assembly. 
       FIG. 99  shows another embodiment of a reduced articulating surface area implant  1410 . Implant  1410  has a substantially annular shape with a curved surface  1412 . When implanted, surface  1412  serves as the bearing surface against which the other joint component articulates. Surface  1412  can be provided with a beveled bearing surface, if desired. The annular shape of implant  1410  defines an interior region  1414 . If implant  1410  were to be used on the femur, implant  1410  would be placed around the femoral head with interior region  1414  in contact with bone. If implant  1410  were to be used on the acetabulum, implant  1410  could be fixed to the bone or freely float within the acetabulum with no fixation. As was the case for implant  1400 , implant  1410  can be used in other joints. 
       FIG. 100  shows another embodiment of a reduced articulating surface area implant  1416 . Like implant  1410 , implant  1416  is a unitary implant that can be implanted through a minimal incision, has a reduced articulating surface area, and does not require extensive removal of bone. Rather than having a ring shape, implant  1410  has a U-shaped body with curved surface  1418  that serves as the bearing surface. 
     Disposable Trial Implants, Instruments, and Other Surgical Implements 
     As previously discussed throughout this specification, the present invention includes disposable surgical implants and instruments. Currently for hip, knee, shoulder, and other joint replacement surgeries (partial or total), there can be six or more trays of instruments and trial implants. Each tray has to be re-sterilized for each procedure. In the case of knee replacement surgeries, one tray may contain femoral trials, one may contain tibial trials, one may contain polyethylene spacer blocks, one may contain tibial cutting instruments, and one tray may contain femoral cutting instruments. 
     This is cumbersome and unnecessary as only a few of these instruments and trial implants need to be made of surgical grade metal and alloys that are rigid and reusable. There is a significant expense in the multiple tray setups. One company, for example, spends over $150 million just to have instruments in the field. Additionally, shipping charges and re-sterilization costs can be significant. The delay due to the shipping and re-sterilization also adds hidden costs and time. Obviously, money and time can be saved if the number of trays for each procedure were reduced. 
     Also, as a company modifies implant systems or instruments, representatives of the company need to update their inventories accordingly. Frequently, companies are unable to charge for the new instruments as an incentive to promote a new system. Although these costs cannot be recovered, they ultimately add to the cost of joint replacement surgeries. 
     These issues can be addressed by a disposable trialing system. For example, the tibial trial base plate  270  ( FIG. 26 ) and other trial components can be made of a light-weight low cost material such as aluminum, injection molded plastic, composite material, and the like. There would be a series of these disposable trial implants in various sizes for the implant system the surgeon intended to use. Each would come pre-packaged in a sterile state. Alternatively, each sterile package could include different components of the same size. In the case of a knee replacement procedure, each sterile package could include a femoral trial, a tibial trial, a patellar trial, and a spacer trial. Preoperatively, the surgeon could obtain an estimate of the needed size from x-rays and other clinical information. Based upon this estimate, one or more sizes of the trial implants would be brought to the operating room or surgical suite. 
     The use of disposable trial implants would reduce the number of trays needed for a given procedure. The use of disposable cutting blocks would further reduce the number of trays. In this regard, the disposable cutting blocks could be made of a material that has color or some other chemical or physical property that would allow the detection of trace amounts of the cutting blocks. This is particularly useful if the cutting blocks are inadvertently scratched so that any debris could be detected and removed. The instruments and trials could have changeable lugs, changeable stems, or similar modularity to allow modification of the position and the rotation. 
     If desired, some or all of the instruments and other disposables could be packaged in a single sterile unit. Some items that could be included in the unit include the instruments, draping, cement, cement mixer, pulsatile lavage, retractors, drill bits, pins, and guide wires. This would save significant time for the operating personnel as they open this unit and it has all the cutting blocks. 
     One advantage of the disposable system is that the disposable cutting blocks could easily be modified for new or updated instrumentation or for customized instrumentation. The disposable system saves the cost and time of cleaning and re-sterilization. Also, the disposable system would improve the sterile technique in the operating room and since these are single use and sterilized there is no risk of cross-contamination going from one patient to another patient. 
     If desired, only a portion of the trial implants or instrumentation could be disposable. For example, the intramedullary rod for distal femoral cutting blocks could be reusable, however, the actual cutting surface, such as the captured guide  4  in 1 block, the mill cut, etc., could be disposable. 
     Program for Learning Minimally Invasive Surgical Techniques 
     As the minimally invasive surgical instruments, implants, systems, and methods disclosed herein represent a significant deviation from those used in open surgical procedures, the present invention includes a program for training surgeons and other health care professionals. The program is a sequential approach in which the trainee starts the training process using an incision of standard length and progressively decreases the incision size as milestones are achieved. 
     The program is sequential learning, analogous to returning to residency or a mini-fellowship. The program can involve a series of visits to a dedicated training sites and/or remote linking, for example via videoconferences or the Internet, to certain training programs. The goal of the program is to allow the trainee to progress from: working with a standard incision, traditionally to learn anatomy; working through a smaller incision, with a combination of prior art instruments and implants and the downsized instruments and implants according to the present invention; and working through a minimally invasive incision to use the instruments, implants, systems, and techniques according to the present invention. As previously discussed, these techniques include minimizing or avoiding joint dislocation, video and fluoroscopic or other radiographic guidance, computer assisted surgical procedures, cannulated instruments and implants, and downsized instruments and implants. 
     The program can include the following training tools, in any combination: lectures and video demonstrations to understand the instruments, both intra and extramedullary, implants, systems, and methods; observation and discussion of live broadcast surgeries; practice using saw bones; practice with cadavers, animal models, or plastic models that have artificial skin, muscle, tissue, ligaments, and bones; virtual reality evaluations; and practice with minimal incisions. 
     Once proficiency with some or all of the training tools have be achieved, which can be determined by grading based on examination, the trainee can be assigned a mentor, a previously certified health care professional. The trainee can be required to visit and observe the mentor during surgery. Additionally, the mentor could visit the trainee at the trainee&#39;s practice and supervise or otherwise monitor the trainee&#39;s techniques. 
     Even after the initial visits between the mentor and trainee, the mentor could be available for consultation by the trainee. The trainee could start probationary work at his practice by initially using an incision that is only slightly smaller than standard incisions. The x-rays, inter-operative pictures or videos, and other case data could be reviewed and graded by the mentor or other certified instructor. Advancement to the next level would only be allowed if the review were satisfactory. The next level could involve a return to some or all of the training tools to practice working through a smaller incision, with a combination of prior art instruments and implants and the downsized instruments and implants according to the present invention. After the training tools are mastered, probationary work by the trainee at this level would be followed by review and grading by the mentor or other certified instructor. Once again, advancement to the next level would only be allowed if the review were satisfactory. The process is repeated for the final level. 
     The program could be implemented so that the trainee must meet given standards in order to receive instrumentation and implants to allow the trainee to perform the procedures independently without supervision. Furthermore, achieving these standards could be required prior to being allowed to promote or advertise proficiency in the techniques. The standards could be coordinated with hospital Institutional Review Boards. 
     The program could be offered through a professional society, such as the American Academy of Orthopaedic Surgeons and the Hip and Knee Society, a commercial entity, or some combination thereof. Continuing Medical Education (CME) credits and grades could be provided. The instructors and preceptors could be certified, with the certification process through a professional society. 
     The trainees could pay a portion of the costs of the program. Trainees would offset the costs of the program from the added revenue from the procedures and possible lower insurance premiums. The costs of the program may be subsidized by governmental agencies and commercial entities, which would benefit from sales and leasing of instruments and implants. Costs could be subsidized by insurers, which would benefit from the lower costs of the procedures compared to traditional open procedures. Finally, costs could also be subsidized by surgical centers, which would benefit from having trained personnel and added revenue from the procedures. 
     In additional to the educational benefits of the program, the program also provides some legal protection to the trainees. Perhaps more importantly, the program affords protection to the patient by ensuring adequately trained medical personnel. 
     CONCLUSION 
     In view of the foregoing description, it is apparent that the present invention relates to a new and improved method and apparatus for use in performing any desired type of surgery on a joint in a patient&#39;s body. The joint may advantageously be a joint in a knee portion  76  of a patient&#39;s leg  70 . However, the method and apparatus may be used in association with surgery on other joints in a patient&#39;s body. There are many different features of the present invention which may used either together or separately in association with many different types of surgery. Although features of the present invention may be used with many different surgical procedures, the invention is described herein in conjunction with surgery on a joint in a patient&#39;s body. 
     One of the features of the present invention relates to the making of a limited incision  114 . The limited incision  114  may be in any desired portion of a patient&#39;s body. For example, the limited incision  114  may be in a knee portion  76  of a leg  70  of a patient. The limited incision  114  may be made while a lower portion  68  of the leg  70  of the patient is extending downward from the upper portion  72  of the leg of the patient. At this time, a foot  74  connected with the lower portion  68  of the leg of the patient may be below a surface  64  on which the patient is supported. The limited incision  114  may be made while the lower portion  68  of the leg  70  of the patient is suspended from the upper portion of the leg or while the lower portion of the leg and/or the foot  74  of the patient are held by a support device. After the incision  114  has been made, any one of many surgical procedures may be undertaken. 
     It is believed that in certain circumstances, it may be desired to have a main incision  114  of limited length and a secondary incision  920  of even smaller length. The secondary incision  920  may be a portal or stab wound. A cutting tool  170  may be moved through the secondary incision  920 . An implant  286 ,  290  and/or  294  may be moved through the main incision  114 . 
     Once the incision  114  has been made, a patella  120  in the knee portion  76  of the patient may be offset to one side of its normal position. When the patella  120  is offset, an inner side  122  of the patella faces inward toward the end portions  124  and  212  of a femur  126  and tibia  214 . 
     Although any one of many known surgical procedures may be undertaken through the limited incision  114 , down sized instrumentation  134 ,  138 ,  186 ,  210  and/or  218  for use in the making of cuts in a femur  126  and/or tibia  214  may be moved through or part way through the incision. The down sized instrumentation may be smaller than implants  286 ,  290  and/or  294  to be positioned in the knee portion  76  of the patient. The down sized instrumentation  286 ,  290  and/or  294  may have opposite ends which are spaced apart by a distance which is less than the distance between lateral and medial epicondyles on a femur or tibia in the leg of the patient. 
     It is contemplated that the down sized instrumentation  134 ,  138 ,  186 ,  210  and/or  218  may have cutting tool guide surfaces of reduced length. The length of the cutting tool guide surfaces may be less than the length of a cut to be made on a bone. A cut on a bone in the patient may be completed using previously cut surfaces as a guide for the cutting tool. 
     It is contemplated that at least some, if not all, cuts on a bone may be made using light directed onto the bone as a guide. The light directed onto the bone may be in the form of a three dimensional image  850 . The light directed onto the bone may be a beam  866  or  868  along which a cutting tool  170  is moved into engagement with the bone. 
     There are several different orders in which cuts may be made on bones in the knee portion of the leg of the patient. It is believed that it may be advantageous to make the patellar and tibial cuts before making the femoral cuts. 
     There are many different reasons to check ligament balancing in a knee portion  76  of the leg of a patient. Ligament balancing may be checked while the knee portion  76  of the leg  70  of the patient is flexed and the foot  74  of the patient is below the support surface  64  on which the patient is disposed. Flexion and extension balancing of ligaments may be checked by varying the extent of flexion of the knee portion  76  of the leg  70  of the patient. In addition, rotational stability of the ligaments may be checked by rotating the lower portion of the leg of the patient about its central axis. Balancing of ligaments may also be checked by moving the foot  74  of the patient sideways, rotating the lower portion  68  of the leg  70  of the patient, and/or moving the foot anteriorly or posteriorly. 
     It is believed that it may be advantageous to utilize an endoscope  352  or a similar apparatus to examine portions of the patient&#39;s body which are spaced from the incision  114 . It is also contemplated that images of the knee portion of the patient&#39;s leg may be obtained by using any one of many known image generating devices other than an endoscope  352 . The images may be obtained while the patient&#39;s leg  70  is stationary or in motion. The images may be obtained to assist a surgeon in conducting any desired type of surgery. 
     Balancing of the ligaments in the knee portion  76  of a patient&#39;s leg  70  may be facilitated by the positioning of one or more transducers  596  and/or  598  between tendons, ligaments, and/or bones in the knee portion. One transducer  598  may be positioned relative to a medial side of a knee joint. Another transducer  596  may be positioned relative to a lateral side of the knee joint. During bending of the knee joint, the output from the transducers  596  and  598  will vary as a function of variations in tension forces in the ligaments. This enables the tension forces in ligaments in opposite sides of the knee portion to be compared to facilitate balancing of the ligaments. 
     Patellar tracking may be checked by the positioning of one or more transducers  930  and/or  932  between the patella  120  and the distal end portion  124  of the femur  126 . If desired, one transducer  932  may be placed between a medial portion of the patella  120  and the distal end portion  124  of the femur  126 . A second transducer  930  may be placed between a lateral portion of the patella  120  and the distal end portion  124  of the femur  126 . Output signals from a transducer  930  will vary as a function of variations in force transmitted between the patella  120  and femur  126  during bending of the leg. 
     The articular surface  122  on the patella  120  may be repaired. The defective original articular surface  122  on the patella  120  may be removed by cutting the patella while an inner side of the patella faces toward a distal end portion  124  of a femur  126 . The step of cutting the patella may be performed while the patella is disposed in situ and is urged toward the distal end portion of the femur by connective tissue. An implant may then be positioned on the patella  120 . 
     It is contemplated that the size of the incision  114  in the knee or other portion of the patient may be minimized by conducting surgery through a cannula  564 . The cannula  564  may be expandable. To facilitate moving of an implant  286 ,  290  and/or  294  through the cannula  564 , the implant may be formed in two or more portions  572  and  574 . The portions of the implant  286 ,  290  and/or  294  may be interconnected when the portions of the implant have been positioned in the patient&#39;s body. Although the implants disclosed herein are associated with a patient&#39;s knee, it should be understood that the implants may be positioned at any desired location in a patient&#39;s body. 
     An implant  626 ,  640  or  670  may be positioned in a recess  610 ,  642  or  672  formed in a bone  126  or  214  in a patient. The implant  626 ,  640  or  670  may contain biological resurfacing and/or bone growth promoting materials. The implant  626 ,  640  and/or  670  may contain mesenchymal cells and/or tissue inductive factors. Alternatively, the implant  626  or  640  may be formed of one or more materials which do not enable bone to grow into the implant. 
     In accordance with one of the features of the present invention, body tissue may be moved or stretched by a device  720 ,  722  and/or  730  which is expandable. The expandable device  720 ,  722  and/or  730  may be biodegradable so that it can be left in a patient&#39;s body. The expandable device  720 ,  722  and/or  730  may be expanded to move and/or stretch body tissue and increase a range of motion of a joint. The expandable device may be used to stretch body tissue in which an incision is to be made. 
     An improved drape system  100  is provided to maintain a sterile field between a surgeon  106  and a patient during movement of the surgeon relative to the patient. The improved drape system  100  includes a drape  102  which extends between the surgeon and a drape  90  for the patient. During surgery on a knee portion  76  of a leg  70  of a patient, the drape system  100  extends beneath the foot portion  74  of the leg  70  of a patient. It is contemplated that the drape system  100  will be utilized during many different types of operations other than surgery on a leg of a patient. 
     An implant  950 ,  970 ,  980 ,  1002 ,  1020 ,  1040  or  1060  may be movable relative to both a femur  126  and a tibia  214  in a leg of a patient during bending of the leg. The implant may include a single member ( FIGS. 59 ,  60 ,  63 ,  64  and  65 ) which is disposed between and engage by end portions of the femur and tibia. Alternatively, the implant may include a plurality of members ( FIGS. 61 and 62 ) which are disposed in engagement with each other. If desired one of the members of the plurality of members may be secured to a bone and engaged by a member which is not secured to a bone. The implant may be secured to soft tissue in the knee portion of the patient&#39;s leg ( FIGS. 63 and 64 ). 
     There are many different features to the present invention. It is contemplated that these features may be used together or separately. It is also contemplated that the features may be utilized in association with joints in a patient&#39;s body other than a knee joint. For example, features of the present invention may be used in association with surgery on vertebral joints or glenoid joints. However, it is believed that many of the features may be advantageously utilized together during the performance of surgery on a patient&#39;s knee. However, the invention should not be limited to any particular combination of features or to surgery on any particular joint in a patient&#39;s body. It is contemplated that features of the present invention will be used in association with surgery which is not performed on a joint in a patient&#39;s body. 
     Thus, while various descriptions of the present invention are described above, it should be understood that the various features can be used singly or in any combination thereof. Therefore, this invention is not to be limited to only the specifically preferred embodiments depicted herein. Further, it should be understood that variations and modifications within the spirit and scope of the invention may occur to those skilled in the art to which the invention pertains. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is accordingly defined as set forth in the appended claims.