Abstract:
The present invention comprises a set of instruments and a method for their use in preparing a knee joint to receive knee implants. The inventive instruments and method are generally suitable for knee joint surgery. Furthermore, they include features that make them suitable for performing minimally invasive knee surgery.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/383,347, filed May 25, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to methods and instruments for performing total knee arthroplasty.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]    Various embodiments of the present invention will be discussed with reference to the appended drawings. These drawings depict only illustrative embodiments of the invention and are not to be considered limiting of its scope.  
         [0004]    [0004]FIG. 1 is a perspective view of the lateral side of a knee.  
         [0005]    [0005]FIG. 2 is a perspective view of a lateral compartment formed in the knee of FIG. 1.  
         [0006]    [0006]FIG. 3 is a perspective view of a tibial template being mounted on a tibia of the knee of FIG. 1.  
         [0007]    [0007]FIG. 4 is a front elevation view of the template of FIG. 3.  
         [0008]    [0008]FIG. 5 is a side elevation view of the template of FIG. 3.  
         [0009]    [0009]FIG. 6 is a perspective view of a tibial guide mounted on the tibia of FIG. 3.  
         [0010]    [0010]FIG. 7 is a perspective view of an alternative embodiment of a guide system for mounting on a tibia.  
         [0011]    [0011]FIG. 8 is a perspective view of the guide system of FIG. 7 mounted on a tibia.  
         [0012]    [0012]FIG. 9 is a top plan view of the guide system of FIG. 7 mounted on a tibia.  
         [0013]    [0013]FIG. 10 is a front elevation view showing a mechanical axis and an anatomic axis of a femur.  
         [0014]    [0014]FIG. 11 is a perspective view of a guide wire being advanced toward the distal end of a femur.  
         [0015]    [0015]FIG. 12 is a front elevation view of the guide wire shown in FIG. 11 disposed within the femur.  
         [0016]    [0016]FIG. 13 is a perspective view of a positioning guide having the guide wire of FIG. 12 attached thereto.  
         [0017]    [0017]FIG. 14 is a perspective view of an alignment pin.  
         [0018]    [0018]FIG. 15 is a perspective view of a template positioned on a pair of alignment pins like that shown in FIG. 14.  
         [0019]    [0019]FIG. 16 is a perspective view of the template shown in FIG. 15 having a cut guide mounted thereon.  
         [0020]    [0020]FIG. 17 is an exploded perspective view of an alternative embodiment of a modular template.  
         [0021]    [0021]FIG. 18 is a perspective view of the template of FIG. 18 with a distal cut stylus installed.  
         [0022]    [0022]FIG. 19 is a perspective view of the template of FIG. 18 with a distal femoral cut guide installed.  
         [0023]    [0023]FIG. 20 is a perspective view of the template of FIG. 18 with an anterior femoral cut guide installed.  
         [0024]    [0024]FIG. 21 is a perspective view of the template of FIG. 18 with a posterior femoral cut guide installed.  
         [0025]    [0025]FIG. 22 is a side elevation view of a set guide for use on a femur.  
         [0026]    [0026]FIG. 23 is a schematic representation of mounting the set guide shown in FIG. 23 to a femur.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    The present invention relates to methods and corresponding instruments for performing minimally invasive total knee arthroplasty. By way of example and not by limitation, depicted in FIG. 1 is a knee  10  having a lateral side  12 . The knee  10  is flexed to about 90 degrees and marks are made on the skin over select areas. Specifically, marks  14  are made over Gerdy&#39;s tubercle, marks  16  are made over the tibial tuberosity, and marks  18  are made over the lateral border of the patella.  
         [0028]    An incision, marked by a dashed line  20 , is made beginning at the mid-portion of the patella and just lateral to the patellar border and extending along the lateral parapatellar region distally to the tibial tuberosity. The incision passes between the tibial tuberosity and Gerdy&#39;s tubercle. The lateral retinaculum is divided in line with the skin incision.  
         [0029]    The lateral edge of the distal incision is now elevated from the bone at the tibia until Gerdy&#39;s tubercle is encountered. At this point Gerdy&#39;s tubercle is elevated, such as with a curved ½-inch osteotome, leaving approximately 2 mm of bone thickness to the illiotibial band insertion at Gerdy&#39;s tubercle. Subperiosteal dissection is then continued laterally along the proximal tibia to the posterior lateral corner. A retractor is put in place which extends around the posterolateral corner to a point midway between the posterior cruciate ligament and the posterolateral corner.  
         [0030]    The anterior half of the lateral meniscus is excised, and a portion of the fat pad is also excised to give full visualization of the lateral compartment. The tissue just proximal to the tibial tuberosity is subperiosteally dissected from the tibial tuberosity to the joint line. Subperiosteal dissection is then carried out medially, elevating the capsule and soft tissue from the joint line to a point approximately 8 mm distal to the joint. This is elevated around the anteromedial corner, and a retractor is put in place containing the patella tendon and the anteromedial capsule. As depicted in FIG. 2, the exposure now reveals a lateral compartment  22 , both anteriorly and laterally, wherein the distal end of a femur  4 , proximal end of a tibia  6 , and a joint line  8  formed therebetween are exposed.  
         [0031]    Optionally, the lateral epicondyle can now be osteotomized. A curved ⅜-inch osteotome is utilized to elevate the base of the lateral epicondyle beginning anteriorly and extending distally to the edge of the articular surface and then elevating it as a Greenstick fracture by leaving the final attachment at the posterior border of the epicondyle. This is elevated sharply, and the attached tendons are retracted posterolaterally to expose the lateral joint and allow for opening with varus stress to expose the posterior horn of the lateral meniscus and the posterior cruciate ligament.  
         [0032]    This optional osteotomy is utilized to give exposure and access to the posterior cruciate to protect this structure when the tibial cut is made from lateral to medial.  
         [0033]    Once the lateral compartment  22  is formed, the tibial plateau of the tibia  6  is resected along a cut plane  5  that is substantially parallel to the joint line  8 . In one embodiment, as depicted in FIG. 3, the proper orientation of the cut plane is determined by initially mounting a tibial template  24  on the anteriolateral side of the proximal end of the tibia  6 .  
         [0034]    The tibial template  24  comprises a base  26  having a front face  28  and an opposing back face  30 . At least two spaced apart passageways  32  extend between the front  28  and back  30  faces. A placement arm  34  having a flat end  35  projecting outwardly from the front face  28  is spaced a predetermined distance from the passageways  32 . A support arm  37  also projects from the front face  28  at the same distance from the placement arm and the passageways  32 . The support arm and passageways are selectively adjustable along the height of the front face  28  to vary their spacing from the support arm  37 . The support arm  37  thus indicates the location on the bone that fasteners will penetrate when inserted through the passageways  32 .  
         [0035]    Finally, an alignment assembly  38  is mounted on the back face  30  of the base  26 . The alignment assembly  38  includes a bracket  36  that is rotatable relative to the base  26  about an axis that is substantially parallel with the longitudinal axis of the placement arm  34 . An elongated rod  39  projects from the bracket  36  at an orientation substantially normal to the long axis of the placement arm  34 .  
         [0036]    The flat end  35  of the placement arm  34  is rested on the lower posterior side of the lateral facet of the superior articular surface of the tibia  6 . The medial-lateral tilt (or varus-valgus angle) of the cut plane for resection of the tibial plateau is set by positioning the rod  39  in parallel alignment with the mechanical axis of the tibia  6 . In one embodiment, this is accomplished by using line-of-sight to position the rod  39  in parallel alignment with the tibial ridge of the tibia  6 , as shown in FIG. 4.  
         [0037]    The anterior-posterior tilt (or posterior slope) for the cut plane is set by orienting the flat end  35  of the placement arm  34 , which is rigidly mounted to the base  26 , in alignment with the plane of the joint line  8 . In one embodiment this is accomplished through feel and line-of-sight, as shown in FIG. 5. Alternatively, by using relative degree markings formed between the bracket  36  and base  26  of the tibial template  24 , the base  26  and the placement arm  34  can be set at a predetermined angle relative to the rod  39  which, as discussed above, is disposed in parallel alignment with the mechanical axis of the tibia  6 . The angle can be set in a range between about 3° to about 7° which is the statistical norm for the posterior slope of the joint line  8 . Alternatively, the angle can be measured by using conventional instruments to measure the change in height between the anterior and posterior side of the superior articular surface.  
         [0038]    Once the tibial template  24  is properly oriented, fasteners  40  (see FIG. 6), such as pins, nails, screws, and the like, are drilled, hammered or otherwise passed through the passageways  32  and into the proximal end of the tibia  6  distal of the cut plane. Tibial template  24  is then removed over the fasteners  40  so that the fasteners  40  remain in place. The fasteners thus establish a datum for referencing the varus-valgus angle and posterior slope of the proximal tibial cut that records, or preserves, this position information after the template is removed.  
         [0039]    As depicted in FIG. 6, a tibial guide  44  is then mounted on the fasteners  40 . Specifically, the tibial guide  44  comprises a body  46  having a front face  48  and an opposing back face  50  with passageways  52  extending therebetween. The passageways  52  of the tibial guide  44  have substantially the same size and spacing as the passageways  32  of the tibial template  24 . However, extra passageways  52  can be provided to allow for vertical fine tuning of the tibial guide  44 . A bounded guide slot  54  also extends between the front  48  and back  50  faces. The tibial guide  44  is advanced so that the fasteners  40  are received within corresponding passageways  52 . A threaded nut  56  or other form of retaining structure is then mounted on the exposed proximal end of each fastener  40  so as to tightly secure the tibial guide  44  to the tibia  6 . As a result of the predetermined positioning of the fasteners  40 , the guide slot  54  defines a cut plane at a predetermined location approximately 10 mm distal of the top of the tibial plateau.  
         [0040]    A stylus  57  can be inserted through the guide slot  54  to visualize where the cut will be made to permit further adjustment if desired. If adjustment is necessary, the tibial guide  44  can be pulled off of the fasteners  40  and repositioned on a different set of passageways  52 . An oscillating saw blade is then passed through the guide slot  54  and used to cut through the proximal end of the tibia  6  along the cut plane from lateral to medial. This cut is completed anteriorly and medially sacrificing the anterior cruciate ligament, but not posteriorly. Prior to removal of the tibial plateau, the bone is resected around the posterior cruciate ligament. In one embodiment, a ½-inch curved osteotome is inserted from the lateral side of the joint with the knee in varus to protect the bone block containing the tibial insertion of the posterior cruciate ligament. A large osteotome is then inserted into the cut and used to elevate the cut proximal tibial bone. The cut bone is put in traction by gripping it with a pair of forceps. The soft tissues are then removed from the periphery allowing extraction of the cut bone.  
         [0041]    In an alternative embodiment, conventional arthroscopic procedures can be used to drill or otherwise resect the bone bounding the posterior cruciate ligament prior to initial cutting of the incision  20 . Arthroscopic procedures can also be used to remove the meniscus and any soft tissue attachments to the proximal tibia that restrict the removal of the cut proximal tibia from the lateral side.  
         [0042]    It is appreciated that there are a number of alternative methods and instruments that can be used in association with resection of the tibial plateau. For example, the tibial template  24  and tibial guide  44  can be combined into a single guide system that does not require changing parts over fasteners  40 . FIG. 7 shows an illustrative embodiment of such a guide system  55 . The guide system  55  comprises a base  58  through which passageways  45  and a guide slot  47  are formed. An elongated rod  49  projects from the base either rigidly or hingedly. A placement arm  51  is mounted on a bracket  59  having a flange  60  projecting therefrom.  
         [0043]    During initial attachment, the flange  60  is inserted into the guide slot  47  so that the base  58  can be properly oriented using substantially the same procedure as discussed above with regard to the tibial template  24 . Once the base  58  is oriented, fasteners  53  are passed through the passageways  45  to secure the base  58  to the tibia  6 . As depicted in FIGS. 8 and 9, the placement arm  51  is then removed from the base  58  so that a blade  62  can be inserted into guide slot  47 . Alternatively, it is also appreciated that base  58  can be formed with a large exposed top surface which functions as a guide without the need for a bounded guide slot. Various instruments such as drills, oscillating chisels, oscillating saws, and other conventional bone cutting instruments can be used to remove the tibial plateau.  
         [0044]    With the tibial plateau removed, the femur  4  and tibia can be moved together to allow more movement in the joint and give more room to access the femur. In this position, a cutting guide is mounted on the lateral side of the distal end of the femur  4  to facilitate selective resection thereof. The cutting guide, however, must be appropriately positioned so that each of the cuts, as discussed below, has a desired orientation.  
         [0045]    As depicted in FIG. 10, the femur  4  has associated therewith both an anatomic axis  64 , which extends centrally along the femoral shaft, and a mechanical axis  66 . The mechanical axis  66  defines the axis through which vertical load is carried by the femur  4 . The mechanical axis  66  extends from the center of the femoral head  68  to the center of the distal end of the femur  4  at an angle approximately 6° from the anatomic axis  64 . The cuts on the distal end of femur  4  are made relative to the mechanical axis  66 . As such, a reference to the mechanical axis  66  is first ascertained.  
         [0046]    By way of example, in one embodiment an incision is made through the skin of the patient in the parapatella region such that the incision is in alignment with the anatomic axis  64 . As depicted in FIG. 11, a guide wire  74  is passed through the incision and drilled into the distal end of femur  4  so as to extend into the medullary canal along at least a portion of the length of the anatomic axis  64 . In one embodiment, the alignment of guide wire  74  with the anatomic axis  64  is established by using fluoroscopic observation simultaneously with drilling of the guide wire  74 . Alternatively, a larger guide wire can be inserted into the medullary cannel and aligned with the anatomic axis  64  through sight and feel.  
         [0047]    As depicted in FIG. 12, the guide wire, or intramedullary rod,  74  includes a main portion  76  and an extension portion  78 . The main portion  76  includes a distal end  80  and an opposing proximal end  82 . The proximal end  82  terminates at a threaded tip  84  which freely projects from the distal end of the femur  4 . During placement, the extension portion  78  is threaded onto the main portion  76 . A drill handpiece is then mounted to extension portion  78  for drilling the guide wire  74  into the femur. Once the guide wire  74  is inserted, extension portion  78  is temporarily removed. In this position, the knee and soft tissue are manipulated so that the proximal end  82  of the main portion  76  or the guide wire  74  is shifted from the incision formed in the parapatella region to the lateral compartment  22 . The extension portion  78  is then reattached to the main portion  76 .  
         [0048]    As an alternative to making an incision in the parapatella region, the knee joint and soft tissue can initially be manipulated so that the guide wire  74  is drilled directly into the distal end of the femur  4  through the lateral compartment  22 . In this embodiment, it is not necessary that the guide wire  74  be comprised of two portions.  
         [0049]    As depicted in FIG. 13, a positioning guide  90  is slidably attached to the guide wire  74 . The positioning guide  90  comprises a substantially U-shaped body  92  having a top side  94  and a bottom side  96  each extending between a first end  98  and an opposing second end  100 . Elongated slots  102  extend between the opposing sides  94 ,  96  at the first end  98 , second end  100 , and a central portion  104  of the body  92 . A first guide stake  106  and a second guide stake  108  are slidably mounted on the ends  98 ,  100  of the body  92 . Each guide stake  106 ,  108  has a pointed distal end  110 . The guide stakes  106 ,  108  are disposed in coaxial alignment with their distal ends  110  facing oppositely. A knob  112  is associated with each guide stake  106 ,  108 . Each knob  112  is threaded through a portion of the body  92  to selectively bear against its corresponding guide stake  106 ,  108  to enable selective fixed attachment of the guide stakes  106 ,  108  to the body  92 .  
         [0050]    A guide border  114 , is positioned on the top side  94  of the body  92 . The guide border  114  comprises an arched plate  116  having a first post  118  projecting upwardly from a first end  120  of the plate  116  and a second post  122  projecting upwardly from a second end  124  of the plate  116 . A plurality of radially spaced apart grooves  128  are recessed along the side of each post  118 ,  122 . Knobs  126  extend through the slots  102  at the first end  98  and central portion  104  of the body  92  and engage the posts  118 ,  122  so as to selectively secure the guide border  114  to the body  92 . The knobs  126  can be loosened to allow the guide border  114  to slide in an arc along the body  92  to change the angle of the guide wire  74  relative to the guide stakes  106 ,  108 . The knobs  126  can be tightened to fix the guide border in place. Depending on the operating parameters, the knobs  126  can be removed and the guide border  114  shifted to the second end  100  of the body  92 .  
         [0051]    A retainer  130  is mounted to the second post  122 . The retainer  130  comprises a collar  132  that encircles the second post  122  and a sleeve  134  that encircles the guide wire  74 . A set screw  136  is threaded through the collar  132  so as to bear against the second post  122  within a select groove  128 . By loosening set screw  136 , the retainer  130  can be selectively raised or lowered along the second post  122 . When the set screw  136  is tightened, the engagement between the set screw  136  and corresponding groove  128  prevents rotation of the retainer  130  about the second post  122  and raising or lowering of the retainer  130  along the second post  122 .  
         [0052]    A pilot  140  is selectively mounted to the first post  118 . The pilot  140  comprises a collar  142  that encircles the first post  118  and a pin guide  144  that projects outwardly from a side of the pilot  140 . A pair of spaced apart channels  150  extend through the pin guide  144  in parallel alignment. A slot  152  is recessed into one end of the pin guide  144  between the channels  150 . An elongated stylus  154  is selectively mounted within slot  152  and projects from it.  
         [0053]    A plurality of ports  146  extend through the collar  142  so as to communicate with the first post  118 . A set screw  148  is threaded into a select port  146  so as to bear against the first post  118  within a corresponding groove  128 . Each port  146  is positioned at a unique predetermined radial position on the collar  142  such that by positioning the set screw  148  in a specific port  146 , the pin guide  144 , and thus the channels  150  therein, rotates to a predefined angle. In the embodiment depicted, nine ports  146  are provided each having a one degree variance. For example, if the set screw  148  is fixed in the number one port, the channels  150  are oriented at a one degree offset from perpendicular to the guide wire  74 . When the set screw  148  is in the number nine port, the channels  150  are oriented at a nine degree offset from perpendicular to the guide wire  74 .  
         [0054]    During operation, the proximal end of the guide wire  74  is slid within the sleeve  134  of the retainer  130  so that the opposing ends  98 ,  100  of the positioning guide  90  are positioned laterally and medially of the knee  10 , respectively. A small stab wound is made over the medial epicondyle and the guide stakes  106 ,  108  are advanced so as to bear against the lateral epicondyle and medial epicondyle, respectively. To enable placement of the stakes  106 ,  108  over the respective epicondyles, it may be necessary to loosen the set screw  136  and slide the retainer  130  along the second post  122 . It may also be necessary to loosen the knobs  126  and slide the plate  116  along the arc defined by the U-shaped body  92  thereby changing the angle of the guide wire  74  relative to the guide stakes  106 ,  108 . Once the stakes  106 ,  108  are appropriately positioned, the knobs  112 ,  126  and set screw  136  are tightened so that the stakes  106 ,  108  and retainer  130  are locked in place. In this position, the guide wire  74  is still disposed in alignment with the anatomic axis of the femur  4  and the guide stakes  106 ,  108  lie along the epicondylar axis. The epicondylar axis will be used to establish the external rotation for subsequent femoral cuts and implant placement.  
         [0055]    The pilot  140  is set at an angle corresponding to the angle between the mechanical axis and the anatomic axis of the femur either before or after attachment of the positioning guide  90  to the guide wire  74 . In one embodiment, this angle is determined in a preoperative procedure by use of standing x-ray. Alternatively, the angle can be set to approximately 6° which is a statistical norm. Again, the desired angle is set by inserting the set screw  148  into a corresponding port  146  on the first post  118  so that the set screw  148  is received within a corresponding groove  128 . This effectively sets the varus-valgus angle for subsequent bone cuts and implant placement.  
         [0056]    Finally, the pilot  140  is also set at a desired anterior-posterior position along the length of the first post  118 . This is set by raising or lowering the pilot  140  along the first post  118  until the free end  155  of the stylus  154  contacts the surface of the lateral anterior femoral ridge. This determination is made by sight and feel. Once the pilot  140  is at the proper orientation, it is secured in place by tightening the set screw  148 . This effectively sets the anterior-posterior position for subsequent bone cuts and implant placement.  
         [0057]    Once the positioning guide  90  is locked in place, alignment pins  160  are passed through the channels  150  of the pilot  140  and drilled, hammered or otherwise advanced into the lateral side of the femur  4 . As depicted in FIG. 14, each alignment pin  160  has a proximal segment  162  and an intermediate segment  164  having a diameter smaller than the diameter of the proximal segment  162 . As such, a proximal annular shoulder  166  is formed between the proximal segment  162  and the intermediate segment  164 . A narrow breakaway segment  168 , a threaded segment  170 , and a distal segment  172  terminating at a sharpened tip  174  extend distally of the intermediate segment  164 . The threaded segment  170  is smaller in diameter than the distal segment  172  thereby forming a distal annular shoulder  173  between the distal segment  172  and the threaded segment  170 . The alignment pins  160  are advanced until the shoulders  166  contact the pilot  140 , thereby precluding further advancement and placing the two pins at the same depth relative to the pin guide  144 . In this position, as shown in FIG. 11, the distal tips of the alignment pins  160  are disposed adjacent to the guide wire  74 .  
         [0058]    Once the alignment pins  160  are placed, the positioning guide  90  is loosened and removed from the knee  10 . The positioning guide  90  is separated from the implanted pins  160  by fracturing each pin  160  at the breakaway segment  168 . The guide wire  74  is also removed from the femur  4 . The two alignment pins  160  now act as datums and record by their placement the desired varus-valgus angle, external rotation angle, and anterior-posterior position as determined during the placement of positioning guide  90 .  
         [0059]    As depicted in FIG. 15, a template  180  is mounted on the alignment pins  160 . The template  180  comprises a substantially U-shaped body  182  having an exposed perimeter edge  190  comprised of a plurality of flat planar surfaces. Specifically, the perimeter edge  190  comprises an anterior surface  192 , an opposing posterior surface  194 , a distal surface  196 , a first chamfered surface  198  extending between the anterior  192  and distal  196  surfaces, and a second chamfered surface  200  extending between the posterior  194  and distal  196  surfaces. In alternative embodiments, it is appreciated that the body  182  need not be U-shaped but can be any substantially square or any other desired configuration that contains the desired surfaces on perimeter edge  190 .  
         [0060]    Body  182  further includes a front face  184 , a back face  186 , and a plurality of spaced passageways  188  extending between them. In one embodiment at least two passageways  188  are disposed adjacent to each surface of the perimeter edge  190 , although a single passageway  188  can be associated with more than one surface. An elongated slot  191  and one or more anchoring ports  202  also extend between the front  184  and back  186  faces.  
         [0061]    As depicted in FIG. 16, the template  180  is mounted on the alignment pins  160  by passing slot  191  over the pins  160  and then threading nuts  204  onto the exposed threaded segments  170  of each pin  160 . The nuts  204  bias the template  180  against the distal annular shoulder  173  of each pin  160  so as to secure the template  180  in place and oriented in the varus-valgus and posterior slope alignment pre-set by the pins. In this position, the template  180  is mounted on the lateral side of the femur  4  with the surfaces  192 ,  194 ,  196 ,  198 ,  200  of the perimeter edge  190  denoting cut planes for the femur  4 . By measuring the distance between each surface of perimeter edge  190  of the template  180  and corresponding outer surfaces of the femur  4 , a template  180  of an appropriate size is selected so that the cuts on the femur  4  are made at the desired thickness. By loosening the nuts  204 , the template  180  can be slid on the pins to adjust the proximal-distal position for subsequent bone cuts and implant placement. Once an appropriately sized template  180  is chosen, positioned, and secured on the alignment pins  160 , additional pins, anchors, screws or other types of fastens are anchored into the femur  4  through the anchoring ports  202 , thereby further securing template  180  to the femur  4 .  
         [0062]    A modular cut guide  210  is selectively mounted on the front face  184  of the template  180 . The cut guide  210  has a bounded guide slot  212  and a pair of spaced apart passageways  214  extending through it. The cut guide  210  is configured such that its passageways  214  can be selectively aligned with each pair of passageways  188  associated with each perimeter edge surface of the template  180 . Screws can be passed through the cut guide passageways  214  and threaded into the template passageways  188  to secure the cut guide  210  to the template  180 . Alternatively, any form of fastener such as screws, nails, pins and the like can be passed through both the cut guide  210  and the template  180  and secured within the femur  4 , thereby also securing the cut guide  210  to the template  180 . By securing the cut guide  210 , a bottom surface  211  of the guide slot  212  is disposed in the same plane as the corresponding surface of the perimeter edge  190  of the template  180 . A saw, drill, chisel or the like is then passed through the guide slot  212  so as to resect the distal end of the femur  4  along the cut plane defined by the guide slot  212  and the corresponding surface of the perimeter edge  190  of the template  180 . Once a cut is completed, the cut guide  210  is moved into alignment with the next perimeter edge surface of the template  180  and another cut is made. As such, each cut is made individually beginning anteriorly and extending distally and posteriorly.  
         [0063]    It is appreciated that the cuts can be formed on the femur  4  using a number of different techniques and apparatus. For example, instead of the cut guide  210  having the bounded slot  212 , a cut guide can be provided which simply provides an enlarged exposed support surface that is disposed in the same plane as the perimeter edge surfaces of the template  180 . The cutting instrument, which can comprise any form of drill, blade, chisel or the like is then supported on the support surface while facilitating the cuts. In like manner, a separate cut guide can be eliminated and simply replaced with a thicker template which also functions as the cut guide. Likewise, the template need not have a cut guiding surface on its perimeter. The cut guide slot alone can guide the cut.  
         [0064]    FIGS.  17 - 21  depict an alternative illustrative embodiment of a template and modular cut guide assembly for use with the alignment pins  160  set in the femur. Referring to FIG. 17 the template  300  comprises a distal cut guide body  302  having opposing first  304  and second  306  side walls, opposing first  308  and second  310  end walls, and opposing top  312  and bottom  314  faces. An axial through bore  316  extends through the cut guide body  302  from the first end wall  308  to the second end wall  310 . A slide lock knob  318  has a threaded shaft (not shown) threaded into a bore in the bottom face  314  in communication with the axial through bore  316 . An implement lock knob  320  has a threaded shaft (not shown) threaded into a bore in the top face  312  in communication with the axial through bore  316 . A pair of pin receiving bores  322  extends through the cut guide body  302  transverse to the axial bore  316 . The pin receiving bores  322  are offset from the axial bore  316  so that pins may pass through them without interfering with the axial bore  316 . The length of each pin receiving bore  322  is extended by a pin sleeve  324  projecting from each side  304 ,  306  of the cut guide body  302 .  
         [0065]    A slide  330  comprises a cylindrical body  332  having an axial through bore  334  extending from a first end  336  to a second end  338 . An annular flange  340  extends radially from the second end  338  and has a diameter larger than the axial through bore of the cut guide body  302 . An elongated slot  342  extends through one side of the slide body  332  in communication with the through bore  334 . The slide  330  is slidably received in the through bore  316  of the cut guide body  302 . Slide lock knob  318  can be threaded further into the cut guide body  302  to bear against the slide  330  and lock it in a desired axial position along the through bore  316  axis. The flange  340  will bottom on the second end wall  310  to prevent the slide  330  from sliding completely through the cut guide body  302 . The shaft of the implement lock knob  320  aligns with the slot  342  when the slide is inserted into the cut guide body  302 .  
         [0066]    An implement  350  includes a working end  352 , a support arm  354 , and a mounting shaft  356 . The base of the arm  354  is larger than the mounting shaft  356  diameter such that a shoulder  358  is formed at the junction of the shaft  356  and arm  354 . The shaft  356  is generally cylindrical with a flat  360  formed along one side. The mounting shaft  356  is slidably received in the axial through bore  334  of the slide  330 . The shoulder  358  will bottom on the second end  338  of the slide such that the working end  352  is located at a predetermined distance from the second end  338 . The implement lock knob  320  can be threaded further into the cut guide body  302  and through the slot  342  in the slide  330  to bear against the slide flat  360  and lock the shaft in a desired axial position along the slide through bore  334  axis. A selection of implements  350  is provided offering different working ends  352 . Each implement in the selection has a mounting shaft for engaging the slide  330  through bore  334  and shoulder for bottoming on the second end  338  to position its working end at a predetermined distance from the second end  338  of the slide.  
         [0067]    FIGS.  18 - 21  depict a progression of implements mounted on the cut guide body for preparing the distal femur. A distal cut stylus  370  has a flat working end  372  defining a reference surface  374 . The working end  372  connects via a support arm  376  to a shaft (not shown) forming a shoulder as described in reference to FIG. 18. The reference surface  374  lies at a known distance and orientation relative to the shaft and shoulder. In the illustrative embodiment, the reference surface  374  lies in a plane generally perpendicular to the shaft at a predetermined distance from the shoulder. The reference surface  374  projects away from the shaft axis toward the femoral bone to position the reference surface  374  in the incision adjacent to the bone.  
         [0068]    A distal femoral cut guide  380  has a cut guide working end  382  for guiding a cutter to cut the distal femur. In the illustrative embodiment, the working end  382  comprises a saw slot  384  for maintaining a saw blade in a desired cutting plane. The working end  382  connects via a support arm  386  to a shaft (not shown) forming a shoulder as previously described. The saw slot  384  lies at a known distance and orientation relative to the shaft and shoulder. In the illustrative embodiment, the saw slot lies in a plane generally perpendicular to the shaft at a predetermined distance from the shoulder. The working end  382  projects away from the shaft axis toward the femur to position the saw slot in the incision adjacent to the bone.  
         [0069]    An anterior femoral cut guide  390  has a cut guide working end  392  for guiding a cutter to make the anterior and anterior chamfer cuts on the distal femur. In the illustrative embodiment, the working end  392  comprises an anterior cut saw slot  394  and an anterior chamfer cut saw slot  396 . The working end  392  connects via a support arm  398  to a shaft (not shown) forming a shoulder as previously described. The saw slots  394 ,  396  lie at known distances and orientations relative to the shaft and shoulder. The working end  392  projects away from the shaft axis toward the femur to position the saw slots in the incision adjacent to the bone.  
         [0070]    A posterior femoral cut guide  400  has a cut guide working end  402  for guiding a cutter to make the posterior and posterior chamfer cuts on the distal femur. In the illustrative embodiment, the working end  402  comprises a posterior cut saw slot  404  and a posterior chamfer cut saw slot  406 . The working end  402  connects via a support arm  408  to a shaft (not shown) forming a shoulder as previously described. The saw slots  404 ,  406  lie at known distances and orientations relative to the shaft and shoulder. The working end  402  projects away from the shaft axis toward the femur to position the saw slots in the incision adjacent to the bone.  
         [0071]    In use, alignment pins  160  are placed in the femur as described above to establish desired varus-valgus angle, external rotation angle, and anterior-posterior position. The pin receiving bores  322  of the cut guide body  302  are slid over the alignment pins  160  until one or both of the pin sleeves  324  bottoms on the femoral bone. A nut can be threaded onto each of the alignment pins  160  to secure the cut guide body in place. The distal cut stylus  370  is then inserted into the slide  330  until its shoulder bottoms on the second end  338  of the slide  330 . The slide  330  is translated axially within the cut guide body  302  through bore  316  until the reference surface  374  contacts the lateral distal condyle. With the distal cut stylus  370  bottomed in the slide  330  the slide lock knob  318  is rotated to lock the slide  330 . This fixes the proximal-distal position of all of the femoral cuts since each cut guide is referenced to the end  338  of the slide  330 . Now the varus-valgus angle, external rotation angle, anterior-posterior position, and proximal-distal position of each cut are now fixed since the cut guides are keyed to the slide  330 , which is locked to the cut guide body, which is in turned fixed in position by the alignment pins through the pin receiving bores  322 . The distal cut stylus  370  is removed from the slide  330 . The distal cut guide  380  is slid into the slide  330  until it bottoms and is locked in place by tightening the implement lock knob  320 . A saw blade is directed through the saw slot  384  to resect the distal femur. The anterior  390  and posterior  400  femoral cut guides are used similarly to make the anterior, anterior chamfer, posterior and posterior chamfer cuts. The anterior  390  and posterior  400  femoral cut guides can be provided in a range of sizes to prepare different sizes of femurs to receive appropriately sized implants.  
         [0072]    In an alternative embodiment, templates can be mounted on the lateral side of the femur  4  without the use of the positioning guide  90 . FIG. 22 depicts a set guide  270  having an exposed perimeter surface  272 . The perimeter surface  272  has a configuration substantially complementary to the perimeter contour of the distal end of the femur  4  taken from a lateral view. A pair of spaced apart passageways  274  extends through the set guide  270 . In one embodiment, the set guide  270  is comprised of a material that is semitransparent to fluoroscopic rays.  
         [0073]    As depicted in FIGS. 22 and 23, the set guide  270  is disposed adjacent the lateral compartment  22  so that the perimeter surface  272  of the set guide  270  is aligned with the perimeter contour of the distal end of the femur  4  taken from a lateral view. In one embodiment, this alignment is assisted by the use of real-time fluoroscopic rays  276  passing through the set guide  270  and the femur  4 . Once the set guide  270  is aligned with the distal end of the femur  4 , fasteners  278  are passed through each of the passageways  274  and into the femur  4 . In one embodiment, the fasteners  278  can comprise the alignment pins  160 . Once the fasteners  278  are placed, the set guide  270  is removed. The template is then mounted on the fasteners  278  in the same way that the template is mounted on the alignment pins  160 . The cutting process is then completed in the same way as previously discussed with regard to the template.  
         [0074]    Once the cuts are made and the bone fragments are removed through the lateral compartment  22 , the template, the cut guide  210  and all related pins and fasteners are removed from the femur  4 . The distal end of the femur  4  is moved laterally to expose the femur through the lateral incision  20 . Conventional cuts are then made on the posterior side of the patella to accommodate a prosthetic patellar articular surface. All of the prosthetic components can then be fixed in place through the lateral incision.  
         [0075]    Closure is obtained by leaving the retinaculum open on the lateral side adjacent to the patella and closing only the retinaculum beginning at the proximal and lateral patella and extending distally to the tibial tuberosity. Gerdy&#39;s tubercle does not have to be reattached, because this has been partially excised in the excision of the proximal tibia, and the iliotibial band is continuous with the aponeurosis over the perineal musculature. It will reattach itself and secure anterolateral stability.  
         [0076]    The above described minimally invasive process for total knee arthroplasty is described with reference to forming incision  20  and thus compartment  22  on lateral side  12  of knee  10 . It is appreciated that the same methods and instruments can be used to perform the minimally invasive procedure on the medial side of knee  10 . The described embodiments are to be considered in all respects only as illustrative and not restrictive. The present invention may be embodied in other specific forms without departing from the spirit and scope of the appended claims.