Patent Publication Number: US-8535383-B2

Title: Systems and methods for compartmental replacement in a knee

Description:
This application is a continuation in part of U.S. application Ser. No. 11/033,614 filed Jan. 12, 2005 (now U.S. Pat. No. 7,258,701 issued Aug. 21, 2007) which in turn claims priority to U.S. provisional application No. 60/535,967 filed Jan. 12, 2004. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to prosthesis for human body joints, and, more particularly, to prosthesis for knees. 
     BACKGROUND 
     Total knee replacement (TKR) surgery and component systems for replacing compartments of a knee in total replacement surgery are well-known. Typically, the surgery involves resecting the distal end of a femur so a femoral component may be mounted to the femur. The femoral component replaces the lateral condyle, medial condyle, and patellofemoral portions of the femur because one or more of these areas of the knee are diseased and are no longer wearing well or providing an adequate range of motion for a patient. 
     In TKR surgery, the proximal end of the tibia is also resected so that a tibial component may be mounted to the tibia to receive the lateral and medial condyles of the femoral component. The tibial component may be comprised of a material having a low coefficient of friction to simulate the meniscus being replaced by the tibial component. 
     Thus, a TKR system includes components for use in three compartments: the medial tibial femoral compartment, the lateral tibial femoral compartment and the patella femoral compartment, for which the opposing areas of the femur, tibia and patella are prepared for mounting. 
     U.S. Pat. No. 3,816,855 discloses one such system. The &#39;855 patent discloses a unitary femoral component in the form of a shell with two condylar portions. The outer surface of the shell is formed to conform to the natural shapings of the corresponding parts of the knee joint. The inner surface of the shell mirrors this shape, presenting a surface that is curved in the medial lateral direction as well as the anterior posterior direction. While providing a number of benefits, the device of the &#39;855 patent suffers from several limitations. 
     The preparation of a subject for TKR surgery usually causes substantial trauma. A large incision is required for insertion of all of the components of a TKR system and the bone resection required for mounting of the components may require extensive recovery time. Thus, single piece replacement components such as the device of the &#39;855 patent require a large incision. 
     In an effort to reduce this trauma, and accordingly, reduce the recovery time associated with such surgery, TKR systems have been developed that provide TKR components in parts that mate to form the larger TKR components. 
     U.S. patent application No. US 2003/0158606 discloses such a system of TKR components. As shown in that application, the femoral component may consist of two or three pieces. Each of these pieces is smaller than the femoral component that they form when they are assembled in the knee. As a result, the incision required for insertion of these pieces is smaller than an incision for a femoral component having all of these pieces in a single component. Likewise, the tibial component consists of two parts, each of which is smaller than the tibial component that they form when assembled in the knee. 
     U.S. patent application No. US2002/0138150 A1 discloses an alternative two-piece femoral component that allows a center part and a condyle part to be pushed onto a femur separately during implantation. The different parts are then joined according to conventional means. The device of the &#39;150 application further describes guides that are intended to aid in tracking of the patella during extreme flexion. 
     However, both the &#39;606 application and the &#39;150 application use traditional methods of attaching the replacement components to the femur and/or to other components. Such methods are limited by the very nature of minimally invasive surgery. For example, the small incision(s) offers a very limited access to the prosthesis implantation site. Thus, any mechanism used to join the components to other components or to the bone must be accessible from the small incision. This necessarily limits the design of the mechanism. Moreover, it is more difficult to ascertain that two components have been properly connected in situ. This problem is exacerbated for components that are designed to be connected with very small tolerances. 
     Moreover, even if the components are precisely connected, problems arise as the replacement components are exposed to different stresses and impacts. Such forces tend to create relative movement between the adjacent components which is exacerbated if the components have been improperly connected. The relative movement of the adjacent components causes rubbing of the components generating frictional debris. The frictional debris tends to move with fluid transfer along the interface between the prosthesis and the surrounding soft tissue, and also tends to enter the intramedullary space between the prosthesis stem and the surrounding remaining bone portion. The biological reaction to these small wear particles causes the surrounding bone tissue to be lysed, thereby weakening the bone and potentially causing additional loosening of the prosthesis and subsequent bone failure. 
     Yet another limitation of implant systems is that as a commercial consideration, many replacement components are mass-produced. While beneficially lowering the cost of implants, these systems are generally provided in a limited number of discrete sizes that most likely will not be precisely the size needed for a patient. For example, a patient&#39;s femur may measure 75-mm in diameter. However, available implants for this patient may measure 70-mm and 80-mm. Thus, a surgeon must replace the natural femur with a component that is either too large or too small. 
     What is needed is a system and method for performing TKR surgery so that wear debris from adjacent pieces of a prosthesis system is reduced. 
     What is needed is a system and method of implanting femoral components that more closely reflects the size of the natural femur. 
     What is needed is a system and a method of implanting femoral components that allow the size of the joined components to be individualized. 
     What is needed is a system and a method of implanting femoral components that provide greater design flexibility in the manner in which adjacent components are connected. 
     SUMMARY OF THE INVENTION 
     The above described needs are met by a system and method that operate in accordance with the principles of the present invention. In one embodiment, a kit for a prosthesis system includes a plurality of first components, each of the plurality of first components for replacing one of a plurality of first surface portions of a bone, a second component for replacing a second surface portion of the bone and a resilient connector for connecting at least one of the plurality of first components to the second component. 
     In a further embodiment, a method of configuring a prosthesis system includes selecting one of a plurality of first components in a kit for replacing a first surface portion of a bone, selecting one of a plurality of second components in the kit for replacing a second surface portion of the bone and connecting the selected first component to the selected second component with a first resilient connector. 
     In yet another embodiment, a method for implanting a prosthesis system includes making an incision, selecting a first component having a bone mounting surface, a bone surface replacement surface, a first side adjacent to the bone mounting surface and the bone surface replacement surface, and a second side adjacent to the bone mounting surface and the bone surface replacement surface, selecting a second component having a bone mounting surface, a bone surface replacement surface, and a side adjacent to the bone mounting surface and the bone surface replacement surface, connecting the first component and the second component such that the first side of the first component is in opposition to the side of the second component, inserting the connected first component and second component through the incision, and mounting the first and the second component on a bone such that the bone mounting surface of the first component and the bone mounting surface of the second component are in opposition to the bone. 
     The above-described features and advantages, as well as others, will become more readily apparent to those of ordinary skill in the art by reference to the following detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a patella femoral component and a tibial femoral component that may be included in a system made in accordance with principles of the present invention; 
         FIGS. 2 and 3  depict exemplary configurations of medial tibial femoral, lateral tibial femoral and patella femoral joint (PFJ) components with trochlear extensions in a system of the present invention; 
         FIG. 4  depicts an exemplary configuration of a PFJ component with nodes in a system of the present invention; 
         FIGS. 5 ,  6  and  7  depict exemplary configurations of medial tibial femoral, lateral tibial femoral and PFJ components in a system of the present invention; 
         FIGS. 8 ,  9  and  10  depict various configurations of the interior of PFJ/condylar components in the anterior to posterior direction in a system of the present invention; 
         FIGS. 11A ,  11 B,  11 C,  11 D and  11 E depict various configurations of the interior of PFJ/condylar components in the medial to lateral direction in a system of the present invention; 
         FIG. 12  depicts a PFJ component with a lateral trochlear extension that may be used in a system of the present invention; 
         FIG. 13  depicts a PFJ component with a medial trochlear extension that may be used in a system of the present invention; 
         FIG. 14  depicts a PFJ component with a medial trochlear extension and a lateral trochlear extension that may be used in a system of the present invention; 
         FIGS. 15A ,  16  and  17  depict PFJ components with a lateral trochlear extension and a medial trochlear extension for use with femurs of varying widths in accordance with features of the present invention; 
         FIGS. 15B and 15C  depict the PFJ component of  FIG. 15A  with one and two shims, respectively, to allow the use of the PFJ component of  FIG. 15A  in patellofemoral areas that are wider than the PFJ component of  FIG. 15A . 
         FIG. 15D  depicts a shim with a flap for attachment to a bone and/or attachment underneath an adjacent component that may be trimmed as needed to be used with the PFJ component of  15 A; 
         FIG. 15E  depicts a shim sheet that may be folded or trimmed to provide the desired dimensions for a shim; 
         FIG. 15F  depicts the shim sheet of  FIG. 15E  folded to provide additional width; 
         FIG. 15G  depicts a shim with a flap for attachment to a bone and/or attachment underneath an adjacent component and a pocket that may be filled and trimmed as needed to be used with the PFJ component of  15 A along with an extension that may be used to seal the pocket; 
         FIG. 18  depicts a faceted interior in the anterior to posterior direction of a patellar femoral component that may be used in a system of the present invention; 
         FIG. 19  depicts a combined flat and curved interior in the anterior to posterior direction of a patellar femoral component that may be used in a system of the present invention; 
         FIG. 20  depicts a curved interior in the anterior to posterior direction of a patellar femoral component that may be used in a system of the present invention; 
         FIG. 21  depicts various cross-sections in the medial to lateral direction that may be used in the anterior portions of the components of  FIGS. 18 ,  19  and  20 ; 
         FIGS. 22 ,  23  and  24  depict embodiments of condyle components with a faceted interior, a combined flat and curved interior, and a curved interior in the anterior to posterior direction that may be used in a system of the present invention; 
         FIG. 22  depicts an embodiment of a condyle component with a faceted interior in the anterior to posterior direction that may be used in a system of the present invention; 
         FIG. 23  depicts an embodiment of a condyle component with a curved interior in the anterior to posterior direction that may be used in a system of the present invention; 
         FIG. 24  depicts an embodiment of a condyle component with a combined flat and curved interior in the anterior to posterior direction that may be used in a system of the present invention; 
         FIG. 25  depicts an embodiment of a condyle component with a faceted interior in the anterior to posterior direction and a posterior extension that may be used in a system of the present invention; 
         FIGS. 26A ,  26 B,  26 C,  26 D and  26 E depict various cross-sections in the medial to lateral direction that may be used in the condyle components of  FIGS. 22 ,  23 ,  24  and  25 ; 
         FIGS. 27 ,  28  and  29  depict embodiments of augments shaped to fit various internal anterior to posterior geometries of components that may be used in a system of the present invention; 
         FIGS. 30A ,  30 B,  30 C,  30 D and  30 E depict various cross-sections in the medial to lateral direction that may be used in the augments of  FIGS. 27 ,  28  and  29 ; 
         FIG. 31A  depicts a split anterior configuration of a tibial femoral and a PFJ component that may be used in a system of the present invention; 
         FIG. 31B  depicts the complimentary tibial femoral component and the PFJ component of  FIG. 31A  implanted so as to abut one another without coupling of the components; 
         FIG. 32A  depicts a partial cross-section of the components of  FIG. 31A  about a bone tide; 
         FIG. 32B  depicts a partial cross-section of the components of  FIG. 31B ; 
         FIG. 33  depicts an alternative partial cross-section of components having different thicknesses about a bone tide that may be used in a system of the present invention; 
         FIG. 34  depicts alternative edge configurations of implants that may be used in a system of the present invention; 
         FIG. 35A  depicts a beaded spacer structure at the interface between components and a bone tide that may be used in a system of the present invention; 
         FIG. 35B  depicts a beaded spacer structure at the interface between two components that may be used in a system of the present invention wherein the spacer beads are complimentarily attached to both of the components; 
         FIG. 35C  depicts an alternative spacer structure with flaps which is configurable for a specific application that may be used in a system of the present invention; 
         FIG. 35D  depicts a patient configuration of a shim spacer structure at the interface between two components that may be used in a system of the present invention to allow components to be used in a variety of patient configurations; 
         FIG. 35E  depicts the shim spacer structure and components of  FIG. 35D  configured for a patient geometry different than the configuration of  FIG. 35D ; 
         FIG. 36  depicts a key structure that may be used at the interface between components in a system of the present invention; 
         FIG. 37  depicts an alternative key structure that may be used at the interface between components in a system of the present invention; 
         FIG. 38  depicts an alternative key structure that may be used at the interface between components in a system of the present invention; 
         FIG. 39  depicts a hinge that may be used at the interface between components in a system of the present invention; 
         FIG. 40  depicts one embodiment of two knee components coupled together with screws at the anterior of a femur that may be used in a system of the present invention; 
         FIG. 41  depicts components connected together by a screw with space, bone or spacer material between the components that may be used in a system of the present invention; 
         FIG. 42  depicts components and spacer material connected together without a screw, with the spacer material between the component that may be used in a system of the present invention s; 
         FIG. 43  depicts a threaded screw coupling of components that may be used in a system of the present invention in which one or more of the screws have different thread pitches; 
         FIG. 44  depicts a component coupling arrangement that uses attachment posts with screws for component coupling that may be used in a system of the present invention; 
         FIG. 45  is a front perspective view of components with an alternative attachment post arrangement for component coupling that may be used in a system of the present invention; 
         FIG. 46  is a side perspective view of the components of  FIG. 45 ; 
         FIG. 47  depicts a single piece component that may be used in a system of the present invention with a screw mechanism used to adjust the relative position of two areas of the component; 
         FIG. 48A  depicts a component coupling arrangement that uses connector receptacles with resilient connectors for component coupling that may be used in a system of the present invention; 
         FIG. 48B  depicts a component coupling arrangement that uses connector receptacles with resilient connectors integrally formed with one component for component coupling that may be used in a system of the present invention; 
         FIG. 49A  depicts a cross section of a resilient connector of  FIG. 48A ; 
         FIG. 49B  depicts an alternative connector with an integrally formed spacer that may be used in a system of the present invention; 
         FIG. 49C  depicts a temporary or permanent spacer that may be used with the resilient connector of  FIG. 49A ; 
         FIG. 50A  depicts a patella component above a gap between implanted components that may be used in a system of the present invention with a notch for facilitating patella movement; 
         FIG. 50B  depicts stepped tibial components that may be used in a system of the present invention; 
         FIG. 50C  depicts a tibial component with a convex meniscus and a concave meniscus that may be used in a system of the present invention; 
         FIG. 51  depicts femoral and tibial components of a total knee replacement with stepped condyle areas that may be used in a system of the present invention; 
         FIG. 52  depicts a stepped unitary PFJ/condyle component with an additional condylar component that may be used in a system of the present invention; 
         FIG. 53  depicts a femoral component with non-divergent condyle areas that may be used in a system of the present invention; 
         FIG. 54  depicts a femoral component with divergent condyle areas that may be used in a system of the present invention; 
         FIG. 55  depicts a tibial component and a femoral component with asymmetrical condyle areas that may be used in a system of the present invention; 
         FIGS. 56 and 57  depict cross-sections of the asymmetrical condyle areas in the anterior to posterior direction of the femoral component of  FIG. 55 ; 
         FIG. 58  depicts an alternative embodiment of a femoral component with asymmetrical condyle areas that may be used in a system of the present invention; 
         FIGS. 59 and 60  depict cross-sections of the asymmetrical condyle areas in the medial to lateral direction of the femoral component of  FIG. 58 ; 
         FIG. 61  depicts the sagittal view of a femoral component with different radii of curvature from the anterior to posterior portions of the component that may be used in a system of the present invention; 
         FIGS. 62 and 63  depict cross-sections in the medial to lateral direction of the femoral component shown in  FIG. 34 ; 
         FIG. 64  depicts components implanted in a femur in optimized positions with respect to patellar and tibial load lines; 
         FIG. 65  depicts components identical to the components of  FIG. 64  implanted in a femur in optimized positions with respect to patellar and tibial load lines; 
         FIG. 66  depicts the different orientations between the components of  FIG. 64  and the components of  FIG. 65  that are possible with components that may be used in a system of the present invention; 
         FIG. 67  depicts a femoral component of a knee replacement that may be used in a system of the present invention; 
         FIGS. 68 ,  69  and  70  depict various possible configurations of the interior of the component of  FIG. 67  in the anterior to posterior direction; 
         FIGS. 71A ,  71 B,  71 C,  71 D and  71 E depict various cross-sections in the medial to lateral direction that may be used in the component of  FIG. 67 ; 
         FIG. 72  illustrates the six degrees of freedom in placement of replacement components made possible by a system of the present invention; 
         FIG. 73  depicts a cutting guide block placed in position for resecting the posterior portion of a femur in accordance with the present invention; 
         FIG. 74  depicts components that have been selected for use in an implant in accordance with the present invention; 
         FIG. 75  depicts a cutting guide block placed in position for resecting the anterior portion of the femur of  FIG. 73  in accordance with the present invention; 
         FIG. 76  depicts the femur of  FIGS. 73 and 75  with the anterior, posterior and distal portions resected; 
         FIG. 77  depicts the femur of  FIG. 76  implanted with the components of  FIG. 74  in accordance with the present invention; 
         FIG. 78  depicts components with some interior surfaces that are parallel to each other that may be used in accordance with the present invention; 
         FIGS. 79A-D  depict an implantation procedure for a patellofemoral component in accordance with the present invention. 
         FIGS. 79E-H  depict an implantation procedure for a condylar component adjacent to the patellofemoral component implanted during the procedure of  FIGS. 79A-D . 
         FIGS. 80A-G  depict an implantation procedure for a prosthesis system that is connected ex vivo in accordance with the present invention. 
         FIG. 81  depicts a femur with a defective area; 
         FIG. 82A  depicts a cutting guide that may be used in accordance with the present invention to resect the defective area of  FIG. 81 ; 
         FIG. 82B  depicts a top perspective view of the guide of  FIG. 82A ; 
         FIG. 82C  depicts a top perspective view of a component that may be implanted into the femur of  FIG. 81  after using the guide of  FIG. 82A  to resect the defective area of  FIG. 81  in accordance with the present invention; 
         FIG. 83  depicts the guide of  FIG. 82A  inserted into the femur of  FIG. 81 . 
         FIG. 84  depicts a tool that may be used with the guide of  FIG. 82A  to resect a portion of the femur of  FIG. 81  in accordance with the present invention; 
         FIG. 85  depicts a path using the guide of  FIG. 82A  along which the tool of  FIG. 84  may be moved to define the area of the femur of  FIG. 81  to be resected in accordance with the present invention; 
         FIG. 86  depicts an alternative tool and guide that may be used to define the area of the femur of  FIG. 81  to be resected in accordance with the present invention; 
         FIG. 87  depicts a punch guide that may be used to define the area of a bone to be resected in accordance with the present invention; 
         FIG. 88  depicts the punch guide of  FIG. 87  with the internal cutting edges removed for clarity; 
         FIG. 89  depicts an alternative punch guide positioned on guide pins that may be used to define the area of a bone to be resected in accordance with the present invention; 
         FIG. 90  depicts a pin guide mounted on an implanted component that may be used to position pin guides in accordance with the present invention; 
         FIG. 91  depicts a saw with guide studs that may be used to resect bone in accordance with the present invention; 
         FIG. 92  depicts a guide that may be used to guide the saw of  FIG. 91  to make a straight resection of a desired depth in accordance with the present invention; 
         FIG. 93  depicts an alternative guide that may be used with a saw with guide studs on opposite sides of the saw housing to make curved resections of a desired depth in accordance with the present invention; 
         FIG. 94  depicts a top perspective view of the guide of  FIG. 93 . 
         FIG. 95  depicts a wire saw that may be used to resect bone in accordance with the present invention; 
         FIG. 96  depicts the saw of  FIG. 95  mounted in a guide which is mounted to a femur wherein the guide enables a curved resection of the femur in accordance with the present invention; 
         FIG. 97  depicts a top perspective view of the guide of  FIG. 96 ; 
         FIG. 98  depicts an enlarged cross-sectional view of the saw of  FIG. 95  mounted in the guide of  FIG. 96 ; and 
         FIG. 99  depicts an alternative guide which is mounted to a femur wherein the guide enables the saw of  FIG. 95  to make a faceted resection of the femur in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Individual Components 
       FIG. 1  shows a system  10  that is comprised of a femoral replacement  12 , a tibial replacement  14 , and a patellar replacement (not shown). The femoral replacement  12  includes a patellofemoral joint (PFJ) component  16 , an upper lateral condyle component  18 , an upper medial condyle component  20 , a lateral femoral anterior/posterior condyle component  22 , and a medial femoral anterior/posterior condyle component  24 . In accordance with one embodiment (not shown) the upper condyle components and femoral anterior/posterior condyle components are provided as a single component. The tibial replacement  14  includes a medial meniscus component  26 , a lateral meniscus component  28 , and a tibial stem component  30 . 
     By segmenting the replacements into upper and anterior-posterior medial, and lateral, PFJ, meniscus and tibial stem components, the system  10  of the present invention enables a surgeon to remove only the diseased portion of a femur or tibia and implant the corresponding component to perform a partial knee replacement. Because the components are smaller than a one-piece construction of the total implant, the incision for the implantation surgery is smaller and the recovery time from the surgery, correspondingly, reduced. 
     Additionally, the replacements allow for complimentary implantation. “Complimentary” replacement components, as used herein, are defined to be components that can be used independently and/or jointly, such that there is no need to remove previously implanted components if additional components are needed at a later time. Furthermore, the complimentary components need not align with one another in a particular orientation after implantation because the components are not shaped to require assembly with adjacent components into a unitary piece. Instead, the surgeon is free to locate a replacement component in accordance with the conditions of a particular bone area. Accordingly, the surgeon need not compromise on local geometry accommodation in order to achieve an overall fit for the component. Thus, the system  10  enables more freedom of movement and orientation of the knee replacement components than has been available with previous compartment replacements. 
     Because the components are both segmented and complimentary, a surgeon may replace only the diseased portion of a bone which may be limited to a single area of the femur. At some later time, if the bone further deteriorates, the further deteriorated portion of the bone may be replaced without the need to remove the initially implanted component. 
     For example, a surgeon may first implant only the PFJ component  16  during a first surgical procedure. Some time later, perhaps years later, the upper medial condylar area may be determined to need replacement. In accordance with the principles of the present invention, a surgeon need only implant the upper medial condyle component  20  adjacent to the previously implanted PFJ component  16 . 
     Those of ordinary skill in the art will appreciate that any of the components shown in  FIG. 1  may be implanted in a number of different sequences and combinations in a number of different surgical procedures. Thus, the anterior/posterior condyle component  24  may be implanted first, with the PFJ component  16  implanted during a later procedure, and the upper medial condyle component  20  implanted during a still later procedure. Alternatively, all of the components shown in  FIG. 1  may be implanted during a single procedure. Moreover, if one implanted component were to become damaged or worn, the single component may be replaced without disturbing other implanted components. 
     Partial Unibody Components 
     To accommodate various arrangements, the patellofemoral joint component  16 , the upper medial condyle component  20 , and/or the upper lateral condyle component  18  may be configured as a partial unibody component. As shown in  FIG. 2 , a PFJ/medial condyle component  32  includes a PFJ area  34  and a medial condyle area  36  in a single piece. The PFJ/medial condyle component  32  may also include a trochlear extension area  38 .  FIG. 3  depicts a PFJ/lateral condyle component  40  having a PFJ area  42 , a lateral condyle area  44 , and a medial trochlear extension area  46 . 
     The lateral trochlear extension area  38  and the medial trochlear extension area  46  enhance patella tracking. In flexion beyond 90 degrees, the patella begins to ride over the trochlear notch in a femur. When portions of the femur have been replaced, incongruities near the trochlear notch facilitate dislocation of the patella as the patella begins to ride over the trochlear notch. The trochlear extensions permit the patella to articulate over the replacement component beyond 90 degrees of flexion without dislocation. A lateral trochlear extension area is particularly important because the patella tends to sublux laterally during such flexion beyond 90 degrees. However, the relatively large lateral trochlear extension area  38  and medial trochlear extension area  46  constrain the potential placement of condylar components. 
     Provision of enhanced tracking without excessive constraints on the placement of condylar components is accomplished by the PFJ component  48  shown in  FIG. 4 . The PFJ component  48  includes the nodes  50  and  52 . The nodes  50  and  52  extend outwardly from the main portion of the PFJ component  48  to a lesser extent than the lateral trochlear extension area  38  and medial trochlear extension area  46  extend from the PFJ/medial condyle components  32  and  40 , respectively. Thus, a condylar component may be placed adjacent to the PFJ component  48  in a number of different orientations. 
     Of course, the medial trochlear extension area  46  may be replaced with a node. Alternatively, as shown in  FIG. 5 , a PFJ/medial condyle component  54  may be made without any medial trochlear area. Likewise, a PFJ/medial condyle component may be made with a node or without a lateral trochlear area. 
     A unitary component may be of substantially smaller size than the unitary components depicted above. By way of example,  FIG. 6  shows a partial unitary component  56  that extends across most of the PFJ area. However, the minimum desired size of partial unitary component is a function of the size of the bone that needs to be replaced. Thus, a unitary component may be fashioned to be substantially smaller than the partial unitary component  56 . One such example is the partial unitary component  58  which is shown in  FIG. 7 . The partial unitary component  58  is generally in the shape of the partial unitary component  56  along the right side of the components as viewed in  FIGS. 6 and 7 . However, the partial unitary component  58  is much smaller than the partial unitary component  56 . 
     In the event that a second area of bone needs to be replaced, another unitary component may be provided as shown by the partial unitary component  60 . The partial unitary components  58  and  60  are effectively a multi-piece version of the partial unitary component  56 , with a gap provided between the partial unitary components  58  and  60  when they are implanted. Those of ordinary skill in the relevant art will appreciate that additional partial unitary components of varying size may be provided within the scope of the present invention. 
     A consideration in planning for multi-piece replacement components, however, is that it is typically desired to avoid splitting partial unitary components along load lines. A load line indicates an area that experiences higher load as a joint moves between flexion and extension. One such load line is shown in FIG.  7  as the load line  62 . In this embodiment, the partial unitary components  58  and  60  have been selected such that the load line  62  extends over the bone that remains intact between the partial unitary components  58  and  60 . By placing bone-component and/or component-component transitions in areas of lower load, a smooth surface is ensured along the load line, resulting in less component wear. 
     Partial unibody components may include a variety of internal geometries in accordance with the present invention.  FIG. 8  shows a PFJ/medial condyle component  64  with a faceted interior in the anterior to posterior direction comprising flat surfaces  66 ,  68 ,  70 ,  72  and  74 .  FIG. 9  shows a PFJ/medial condyle component  76  with a curved interior surface  78 .  FIG. 10  shows a unitary component  80  with a combined curved and flat interior comprising a curved surface  82  and a flat surface  84 . Of course, any of the components may be constructed with any of the interior geometries shown herein. 
     Moreover, the interior surfaces may be constructed with a variety of geometries in the medial to lateral direction. By way of example, but not of limitation,  FIG. 11A  shows a flat interior  86  taken across line A-A of  FIG. 8 ,  9  or  10 .  FIG. 11B  shows a curved interior  88  while  FIG. 11C  shows a faceted interior  90 .  FIG. 11D  shows interior  92  with curved sides and a flat bottom while  FIG. 11E  shows an interior  94  with flat sides and a curved bottom. These shapes accommodate local bone geometry better than previous known shapes and enable the surgeon to leave more healthy bone in the joint regardless of whether the component is to be press-fit or cemented to the healthy bone. 
     Modified Individual Component 
       FIG. 12  depicts an alternative embodiment of a PFJ component  96  having a lateral trochlear extension area  98  while  FIG. 13  depicts an alternative embodiment of a PFJ component  100  having a medial trochlear extension area  102 .  FIG. 14  shows a PFJ component  104  having both a medial trochlear extension area  106  and a lateral trochlear extension area  108 . 
     PFJ components may be provided in varying widths for a given anterior to posterior length. By way of non-limiting example,  FIGS. 15A ,  16  and  17  are intended to provide relative size comparison. As shown in  FIGS. 15A ,  16  and  17 , a PFJ component may be narrow, (PFJ component  110 ), wide (PFJ component  112 ), or somewhere in between (PFJ component  114 ). 
     Additionally, a PFJ component may be adapted for use in a PFJ area that is wider that would normally be serviceable with a particular PFJ component. Specifically,  FIG. 15B  shows the PFJ component  110  implanted on a femur  111 . The width of the diseased portion of the femur, however, was greater than the width of the PFJ component  110 . In every other respect, however, the PFJ component  110  fits the anatomy of the patient very closely. Accordingly, rather than using a larger PFJ component and introducing undesired variances between the implant and the natural bone, a shim  113  was used to replace the portion of the surface of the femur  111  adjacent to the PFJ component  110 . 
     Moreover, in the event the surface area of the femur  111  to be removed is larger than the width of a replacement PFJ component on both the medial and lateral sides, a second shim may be used. Thus, as shown in  FIG. 15C , the PFJ component  110  and the shim  111  are augmented with a second shim  115 . 
     Accordingly, one or more shims may be used to fit a narrow PFJ component onto a wider PFJ area. This is particularly beneficial when a PFJ component has the desired anterior/posterior dimensions, but is too narrow for the particular replacement. As discussed in further detail below, the shims may be rigidly or flexibly connected to a PFJ or other component either prior to implanting the component or after implantation. Thus, in one embodiment, a component is provided preconfigured with at least one shim that may be trimmed to fit a particular patient. In alternative embodiments, the shim is spaced apart from the component such as by using spacer beads (see  FIG. 35B ). 
     In one embodiment shown in  FIG. 15D , a single sized shim  117  is provided with a flap  119 . The flap  119  is configured to be placed underneath an adjoining component. The flap  119  includes a hole  121  to facilitate connection to a bone. The flap  119  may thus be attached directly to the bone using a tack through the hole  121  or using bone cement. The adjoining component is then implanted on top of the flap  119 . In this embodiment, the shim  117  is flexible and oversized. That is, the shim  117  is wider than would be required in most situations. Accordingly, once the actual dimensions of the area for which a shim is to be used is determined, the shim  117  is resected to the desired dimensions. 
     Another embodiment of a shim is shown in  FIG. 15E . The shim  123  is a sheet of material that may be formed to the desired dimensions. For example, the shim  123  may be folded in the direction of the arrow  125  to provide the configuration shown in  FIG. 15F . The shim  123  in  FIG. 15F  is folded in half so as to double the width of the shim  123  when the shim  123  is implanted. The shim  123  may be folded more than once to provide additional width. Additionally, the shim  123  may be folded lengthwise, crosswise, or in any other desired manner. The shim  123  may further be cut, such as along the dashed line  127  to the desired height. 
     In yet a further embodiment, a shim  129  shown in  FIG. 15G  is provided with a pocket  131 . The pocket  131  includes an open end  133  and a closed end  135 . The shim  129  further includes a flap  137  and an extension  139 . A desired amount of material such as bone chips, biologic material or some other biocompatible material may be placed in the pocket  131  to provide a shim of the desired size. The pocket  131  may be sealed prior to implantation or during implantation, such as by insertion of tack through the end  133 . The flap  137  may also be used to tack the shim  129  into place or the flap  137  may be placed underneath an adjacent component. Alternatively, the flap  137  may be rolled over the top of the pocket  131  and the extension  139  may be used to seal the pocket  131 . 
     A shim may be made from a variety of materials. By way of example, shims may be made from biologically active, inactive or passive materials including fabrics, bone chips and flexible materials. Additionally, in the event some gap remains, filler material such as bone wax, cement, polyurethane or other flexible or biological material may be used to fill the gap. 
     Returning to the discussion of PFJ components, the PFJ components may include a variety of internal geometries in accordance with the present invention.  FIG. 18  shows the PFJ component  96  of  FIG. 12  with a faceted interior in the anterior to posterior direction comprising a flat surface  116  and a flat surface  118 .  FIG. 19  shows the PFJ component  104  of  FIG. 14  with a combined curved and flat interior comprising a flat surface  120  and a curved surface  122 .  FIG. 20  shows the PFJ component  100  of  FIG. 13  with a curved interior  124 . Of course, any of the PFJ components may be constructed with any of the interior geometries shown herein. 
     The cross-section of these components in the medial-lateral direction may also be formed in a variety of shapes, such as cross-sections (a), (b), (c), (d) and (e) shown in  FIG. 21 . As shown in these figures, the cross-section taken along line A-A of  FIG. 18 ,  19  or  20  may comprise flat areas, curved areas, and combinations of flat and curved areas. 
     Unicondylar Components 
     Similarly, unicondylar components, such as lateral condyle components  126 ,  128 , and  130  and medial condyle components  132 ,  134 , and  136  of  FIGS. 12 ,  13  and  14 , may contain various internal geometries, as shown in  FIGS. 22 ,  23  and  24 .  FIG. 22  shows the medial condyle component  132  with a faceted interior in the anterior to posterior direction comprising a flat surface  138 , a flat surface  140  and a flat surface  142 .  FIG. 23  shows the medial condyle component  136  with a curved interior  144  in the anterior to posterior direction and  FIG. 24  shows the lateral condyle component  126  with a combined curved and flat interior comprising a flat surface  146  and a curved surface  148  in the anterior to posterior direction. 
     Moreover, the unicondylar components may be configured to provide for extended flexion. Extended flexion is provided by the extended posterior portion  150  of the condyle component  152  shown in  FIG. 25 . The extended portion provides additional surface area for contact with a tibia as the tibia is rotated about the femur. Of course, any of the condyle components may be constructed with any of the interior geometries shown herein. Moreover, extended flexion may similarly be provided in unibody construction by extension of the condylar area. 
     The cross-section of the condyle components in the medial-lateral direction may also be formed in a variety of shapes, such as those shown in  FIGS. 26A ,  26 B,  26 C,  26 D and  26 E. As shown in these figures, the cross-section taken along line A-A of  FIGS. 22 ,  23  and  24  may comprise flat areas, curved areas, and combinations of flat and curved areas. More specifically,  FIG. 26A  shows a flat interior  154 .  FIG. 26B  shows a curved interior  156  while  FIG. 26C  shows a faceted interior  158 .  FIG. 26D  shows an interior  160  with curved sides and a flat bottom while  FIG. 26E  shows an interior  162  with flat sides and a curved bottom. Combinations of curved and flat geometries are not limited to these figures. Moreover, these internal geometries may be used with all implant components disclosed herein and are not limited to unicondylar components. 
     Augments 
     To further facilitate accommodation of local bone geometry, augments may be placed between a component and a portion of resected bone. The use of augments further provides for reconstruction of a knee that more closely resembles the natural knee without the need for a large number of PFJ and/or condylar components as the augments may be configured to effectively enlarge the outer boundary of the PFJ and/or condylar components. Thus, as shown in  FIGS. 27 ,  28  and  29 , augments  164 ,  166 ,  168 ,  170 ,  172  and  174  may be placed between an implant component and a bone, thus moving the implant components farther away from the bone. 
     The outer surface of an augment is shaped to conform to the interior surface of the component. For example, the exteriors of augment  164  and augment  166  are faceted in the anterior to posterior direction to fit within the faceted interior of component  176 . Augments  168  and  170  are curved to fit within the interior curve of component  178 . Augment  172  is flat to fit against the flat portion of the inner surface of component  180 , while augment  174  is curved to fit against the curved inner portion of component  180 . 
     Of course, the inner portion of the cross-section of the augments in the medial to lateral direction may be shaped similarly to the inner portion of the condyle components discussed above. Thus, a variety of cross-sectional shapes may be realized by various combinations of faceted, curved and straight inner contours with faceted, straight and curved outer contours. 
     By way of example, but not of limitation,  FIG. 30A  shows an augment  182  with a faceted inner surface  184  as well as a faceted outer surface  186 . The augment  182  of  FIG. 30A  may be used with a component having the cross-section shown in  FIG. 26C . The augment  188  shown in  FIG. 30B  may also be used with a component having the cross-section shown in  FIG. 26C . However, instead of a faceted inner surface, the inner surface  190  of augment  188  is curved. The augments  192 ,  194  and  196  of  FIGS. 30C ,  30 D and  30 E may be used with a component having the cross-section shown in  FIG. 26E , so as to realize an inner surface that is faceted (inner surface  198  of augment  192 ), flat (inner surface  200  of augment  194 ), or curved (inner surface  202  of augment  196 ). 
     Joining and Fitting Mechanisms 
       FIG. 31A  shows yet another embodiment of a femoral replacement component  204  that comprises a combined PFJ and lateral condyle area  206 , and a medial condyle area  208 . Alternatively, a component  204  may include an upper condyle area and a lower condyle area. As shown in  FIG. 31A , component pieces  206  and  208  may be implanted about a bone tide  210 . A close-up of the junction between component pieces  206 ,  208 , and bone tide  210  is shown in  FIG. 32A . Bone tide  210  may be comprised of bone, cartilage or a synthetic material. 
     In this embodiment, the component pieces  206  and  208  are configured to be complimentary. Thus, if desired, a surgeon may implant the component pieces  206  and  208  without a bone tide. Thus, as is depicted in  FIG. 31B , the components  206  and  208  are abutted and as depicted in  FIG. 32B , the components  206  and  208  are not coupled. 
     With reference to  FIG. 33 , an alternative embodiment of a bone tide junction is shown. In this embodiment, bone tide  212  is located between component pieces  214  and  216 . Component pieces  214  and  216  have different depths. According to a further embodiment, component pieces may be formed with ends of a variety of shapes. Thus, as shown in  FIG. 34 , component piece  218  is angled inwardly from the upper surface of the component piece  218 , component piece  220  is angled outwardly from the upper surface of the component piece  220 , component piece  222  has a square end, and component piece  224  is radiused. 
     The radiused end of a component piece may include a plurality of segments of different radii of curvature, with a first segment having a radius of curvature larger than a second segment, the second segment located between the first segment and the side of the component. Such a configuration is useful in reducing friction along a load line that passes over the junction of adjacent components. The slight curvature of the edges ensures that an object traveling along the load line does not encounter a ridge resulting from a misalignment of the components when passing from one component to the adjacent component. 
     Components made in accordance with the principles of the present invention may be inset into resected bone or a bone tide. To enhance the retention of the components in the resected area, bead spacers may be formed in the sides of components. As shown in  FIG. 35A , component  226  includes bead spacers  228  and  230 . Similarly, component  232  includes bead spacers  234  and  236 . To use bead spacers in a cementless application, a rescission is made in the bone that comports with the size of the replacement component without the bead spacers. Thus, when the component is inserted into the resected area, the bead spacers are forced tightly against the bone in the wall of the rescission. Bead spacers may be in the form of a single bead, a partial ridge about the component, or a continuous ridge. Those of ordinary skill in the art will appreciate that alternative materials may be used to maintain the components in the desired location in place of or in addition to bead spacers including, but not limited to, porous coatings, orthobiologic materials, lacey membranes, grouting, and cement. 
     Moreover, the spacer beads may be used when two components are to be implanted side by side.  FIG. 35B  shows component  221  with bead spacer  223 . Similarly, component  225  includes bead spacer  227 . In this embodiment, both of the components include bead spacers. In such embodiments, it is preferred to arrange the bead spacers so that they do not interfere with bead spacers on an adjacent component as this would increase the minimum distance between the adjacent components. In the event that there is relative motion between the components  221  and  225 , the edges of the components  221  and  225  will not rub against each other since the spacers  223  and  227  maintain a minimum separation between the components  221  and  225 . 
     Of course, the bead spacers  223  and  227  may contact the adjacent component  225  or  221 , respectively. Thus, in certain embodiments it is desirable to either make the bead spacers  223  and  227  from a resilient material or to coat the bead spacers  223  and  227  with a resilient material. Moreover, the gap between the components that is maintained by the bead spacers  223  and  227  may be filled with a bone wax, cement, polyurethane or other flexible or biologic material to provide additional stability while reducing wear products. 
     A number of alternative embodiments of spacers and spacer configurations are contemplated within the scope of the invention. By way of example, in one embodiment, only one component includes bead spacers. In such an embodiment, the bead spacer may be formed with the component or may be attached to the component at a later step. 
     In a further embodiment, the spacer is not attached to either component. By way of example,  FIG. 35C  shows a spacer device  229  that includes a number of spacers  231  on a substrate  233 . The substrate  233  includes a number of attachment holes  235  and flaps  237  and  239 . The attachment holes  235  may be used to tack the spacer device to a bone. The flaps  237  and  239  are configured to be placed underneath adjacent replacement components. Thus, the spacers  231  are between the adjacent sides of the adjacent components. In this embodiment, the substrate  233  is made of a flexible material. This allows the spacer device  231  to be positioned along a curved component. Moreover, the spacer device  231  may be cut so as to only provide a limited number of spacers  231 . Thus, the spacer device  231  may be individualized for a particular implant scenario. 
     Of course, the spacers need not be in the shape of a bead, box or other symmetrical shape. Spacer shim  233  shown in  FIG. 35D  is generally wedge shaped. Thus, the shim  233  may be wedged between the patellofemoral component  235  and the condylar component  237  to provide additional stability to the replacement components as well as ensuring that the patellofemoral component  235  and the condylar component  237  do not come into direct contact with one another. It is contemplated that in certain embodiments, the shim  233  may be cut during the operation to the desired length. Accordingly, the shim  233  may be cut along the line  239  to minimize bone resection. 
     The use of shims of various shapes, such as the wedge shape of shim  233 , allows for the same replacement components to be used in a range of patient geometries. By way of example,  FIG. 35E  depicts a femur with a condyle  241  that is turned inwardly as compared with the condyle  243  of  FIG. 35D . By simply inserting the shim  233  further between the adjacent patellofemoral component  235  and the condylar component  237 , the same patellofemoral component  235  and condylar component  237  may be used as shown in  FIG. 35E . Thus, the shim  233  allows for different pose of the components. By making the shim in a more complex shape, such providing different tapers along different sides, even greater flexibility may be achieved. 
     Of course, the various spacing components may also be used in different combinations. By way of example, a shim may include spacer beads along its sides. Moreover, additional spacers may be provided on the components or spacers may be provided that are attached to the components as needed. Thus, a significant increase is realized in the ability to use a limited number of components in a wide range of patient geometries. 
     The spacers may be made from a variety of materials. By way of example, spacers may be made from biologically active, inactive or passive materials including fabrics, bone chips and flexible materials. Additionally, in the event a spacer does not completely fill the area between adjacent components or between a component and the adjacent bone, filler material such as bone wax, cement, polyurethane or other flexible or biological material may be used to fill the gap. 
     Implantation of components may also be enhanced by coupling components to one another. To enhance the press fitting between components, a component may be formed with a key that mates with an inverse key of another component. By way of example, as shown in  FIG. 36 , the component  240  includes a key  242  that mates with the key  244  of the component  246  along the entire junction of the components  240  and  246 . 
     Alternatively, a single key may be used to engage components together as shown in  FIG. 37  wherein the key  248  of the component  250  mates with the key  252  of the component  254 . An alternative form of the single key is shown in  FIG. 38  where component  256  has an extending button  258  and the component  260  has button receptacle  262  to receive the button  258 . Keys may thus comprise a single mating element or may comprise a plurality of mating elements. Moreover, use of different types of keys in conjunction with each other may be desired when fitting components. These alternative embodiments are within the scope of the present invention. 
     In another alternative embodiment, a hinge may be formed between components to support movement without component separation. As shown in  FIG. 39 , the component  264  is joined to the component  266  by a hinge  268 . The hinge  268  may be a traditional mechanical hinge. Alternatively, the hinge  268  may be made from a synthetic material that is deigned to yield under force. The use of two components joined by a hinge as opposed to a single component or firmly joined components reduces the chance of a fracture. For example, if the components  264  and  266  are formed as a single rigid component, and if one end of the rigid component is firmly set in bone or cement and a second end of the rigid component is not fully underlain with cement, or if the bone under the second end of the rigid component is compressed, the rigid component will flex at a location between the first and second end. Such flexing or working of the rigid component leads to a stiffening of the material in the rigid component which may result in brittle fracture. However, when joined in the manner shown in  FIG. 39 , the hinge  268  allows for flexure or movement between the two components  264  and  266  without working any material. 
     Femoral, patellar and/or tibial components may also be connected one to another by mechanical means, such as screws. Thus,  FIG. 40  shows a component  270  joined to a component  272  by screws  274  and  276 . The components may be, but need not be, abutted to be joined. With reference to  FIG. 41 , the components  278  and  280  are shown separated by a space generally indicated as the space  282 . A screw  284  may be used to connect the component  278  to the component  280  while maintaining the space  282  between the component  278  and the component  280 . 
     Furthermore, the connection of components may be made either on the same bone or alternatively across the joint space between bones. By way of example,  FIG. 42  depicts PFJ/condyle component  286  connected to spacer  288 , which is in turn connected to tibial component  290 . Connection is made by connectors  292 . The connectors between components may be bone, artificial tissues and/or grafts. 
     The screws may also pass through bores in a bone to hold component sides opposed to one another through the bone. With reference to  FIG. 43 , a component  294  and a component  296  are located against a femur  298  which has a bore  300  therethrough. Accordingly, the component  294  and a component  296  may be joined by insertion of a screw  302  through the bore  300  while the screw  304  joins the components  294  and  296  underneath the femur  298 . As further shown by screw  304 , the screws may be provided with threads  306  and  308  which are different pitches to help control the clamping force. In this embodiment, head  310  of screw  304  includes a receptacle  312  to receive a torque control wrench to facilitate installation of the screw  304 . 
       FIG. 44  shows a femoral component that may be joined by screws in the manner discussed with respect to  FIG. 43 . A unitary component  314  that includes a PFJ area, a medial condyle, and a lateral condyle may be adjustably joined to the posterior condyles  316  and  318  by screws  320 ,  322 ,  324 , and  326 . Components  314 ,  316  and  318  are thin implant components that in this embodiment are curved in the anterior/posterior direction as well as the medial/lateral direction. Components that are not so curved are considered to be within the scope of the present invention, as are components with internal geometries which have been discussed above. 
     Attachment posts  328 ,  330 ,  332 ,  334 ,  336 ,  338 ,  340 , and  342  are formed in components  314 ,  316 , and  318  to extend from the interior surfaces of the components. Screws  320 ,  322 ,  324 , and  326  may be placed through the attachment posts  328 ,  330 ,  332 ,  334 ,  336 ,  338 ,  340 , and  342  so the posts provide additional support for coupling of the components without sacrificing a large amount of bone for implanting of the components. 
     An alternative embodiment is shown in  FIG. 45  where a PFJ component  344  is coupled by vertically oriented screws  346  and  348  to a medial condyle component  350  and to a lateral condyle component  352 . The condylar components  350  and  352  include attachment posts  354  and  356  extending from the components  350  and  352 , respectively, in the medial/lateral direction.  FIG. 46  is a side view of the components of  FIG. 45  showing the PFJ component  344  connected to the medial condyle component  350  by the screw  346 . A screw  358  is inserted through the attachment posts  354  and  356  to join the condylar components  350  and  352 . Alternatively, the medial condyle component  350  and the lateral condyle component  352  may be formed as a unitary component. 
     Screws may also be used in components to provide a surgeon with the ability to change the position of an implanted component relative to another component.  FIG. 47  shows an embodiment including a single piece component  360  with a screw mechanism  362  for lateral/medial adjustments between the PFJ area  364  and the medial condyle area  366 . The ability to mechanically modify the relative positions of areas of a component in this manner enables a surgeon to better match the component to the local implantation geometry. 
     Components may further be resiliently connected. By way of example, the PFJ component  800  may be connected to the condylar components  802  and  804  by the resilient connectors  806  and  808 , respectively. The resilient connector  806  engages the connector receptacle  810  on the PFJ component  800  and the connector receptacle  812  on the condylar component  802 . Similarly, the resilient connector  808  engages the connector receptacle  814  on the PFJ component  800  and the connector receptacle  816  on the condylar component  804 . Suitable resilient materials include nitinol, polyurethanes, elastomers and liquid metals. 
     In an alternative embodiment, the resilient connectors are integral to one of the components to be connected. With reference to  FIG. 48B , the PFJ component  820  is configured much like the PFJ component  800  and includes connector receptacles  822  and  824 . The condylar components  826  and  828 , however, include resilient connectors  830  and  832 , respectively. By providing the condylar components  826  and  828  with the integral resilient connectors  830  and  832 , the number of components within a kit is reduced. 
     Returning to  FIG. 48A , the resilient connectors  806  and  808  are symmetrical. That is, either end of either of the resilient connectors  806  and  808  may be inserted into any of the connector receptacles  810 ,  812 ,  814  or  816 . This is useful in minimizing the number of components that are required in a kit that is used to individualize a prosthetic system for a particular implantation as the same connectors may be used with any of a variety of PFJ components and condylar components. 
     In certain instances, however, the resilient connectors and connector receptacles may be formed so as to reduce the potential for incorrectly connecting adjacent components. By way of example, in the event a condylar component comprises two subcomponents, the connector receptacles used to connect the two subcomponents may be configured differently from the connector receptacles used to connect the condylar component to a PFJ component. Thus, improper positioning of the condylar subcomponents may be prevented. 
       FIG. 49A  depicts a cross-sectional view of the resilient connector  806  positioned to be inserted into the connector receptacle  812 . The resilient connector  806  includes a stem portion  840  and two end portions  842  and  844 . Each of the end portions  842  and  844  include flared portions  846  and  484 , respectively that define cavities  850  and  852 . The connector receptacle  812  includes a channel  854  and a chamber  856 . The diameter of the channel  854  is slightly larger than the diameter of the stem portion  840  and slightly smaller than the diameter of the flared portion  848 . The chamber  856  is slightly larger than the end portion  844 . 
     Accordingly, as the resilient connector  806  is forced into the connector receptacle  812 , the cavity  852  allows the flared portion  848  to bend inwardly so as to fit within the channel  854 . Once fully inserted, the flared portion  848  is allowed to resiliently return to the condition shown in  FIG. 49A , but within the chamber  856 . Since the diameter of the flared portion  848  is greater than the diameter of the channel  854 , the resilient connector  806  is inhibited from being withdrawn from the connector receptacle  812 . 
     Moreover, further movement of the resilient connector  806  toward the connector receptacle  812  is inhibited since the end portion  844  abuts the chamber  856 . Thus, the stem portion  840  of the resilient connector  806  may be used to space apart the PFJ component  800  from the condylar component  802 . Such spacing reduces the production of wear debris in the event that there is relative motion between the PFJ component  800  and the condylar component  802  after implantation. 
     In an alternative embodiment shown in  FIG. 49B , a resilient connector  860  includes a spacer  862  integrally formed into the stem portion  864  of the resilient connector. Alternatively, the components may be coated with a resilient material so as to minimize the production of wear products. When coating the components, it is only necessary to coat the portions of the components that may rub against adjacent components. Of course, only one of the adjacent components need be coated in order to provide the desired reduction in wear debris. 
     In yet a further embodiment, a separate spacer  866  shown in  FIG. 49C  may be used with the resilient connector  806 . The spacer  866  includes a bridging portion  868  and a stem portion  870  with a bracket  872 . The bridging portion  868  is configured to straddle the stem portion  840  of the resilient connector  806 . The stem portion  870  is used to manipulate the spacer  866  into position and the bracket  872  is used to attach a lanyard to the spacer  866  to ensure the spacer  866  is easily located in the event that it becomes dislodged in situ. The spacer  866  may be used to temporarily provide a desired spacing of components as the gap between the components is filled. Alternatively, the spacer  866  may remain in position. In such an application, the stem  870  is cut after the gap between the components is filled and the stem  870  is then removed. 
     Tibial and Patellar Components 
     Referring now to  FIG. 50A , a patellar component  368  is shown above two implanted femoral components  367  and  369 . The patellar component  368  includes a notch  370  that accommodates split anterior designs such as the one shown in  FIG. 40 . Notch  370  reduces impingement of the patella on the junction of a femoral implant. Alternatively, a flat region may be used instead of the notch  370  to reduce impingement on the junction of a femoral implant. 
     Moreover, the slight curvature at the upper edges of the femoral components  367  and  369  reduce potential friction that may result from even slight misalignment of the femoral components  367  and  369 . Similarly, the femoral components  367  and  369  are designed to be implanted with a slight gap  371  between the components along the adjacent edges of the femoral components  367  and  369 . The gap  371  reduces the potential for frictional contact between the femoral components  367  and  369  in the event of relative motion between the two components. However, as is apparent from  FIG. 50A , the gap  371  is designed to be small enough so that another bone passing over the gap, in this embodiment the patellar component  368  passes freely over the gap  371 . 
     An embodiment of a tibial component is shown in  FIG. 50B . Tibial component  372  is stepped to provide a higher support platform for the lateral meniscus  374  than for the medial meniscus  376 . This configuration accommodates the asymmetrical condyles of component  378 . As shown in  FIG. 50C , a medial meniscus  380  may be formed with a concave surface  382  while the lateral meniscus  384  may be formed with a convex surface  386 . Such a configuration of meniscus components better conform to normal knee anatomy. 
     Stepped Components 
     In addition to the various geometries and configurations discussed above, the present invention provides components for a variety of irregularly shaped bone geometries.  FIG. 51  depicts a total knee system  388  with stepped femoral component  390  and stepped tibial component  392 . The medial side  394  of the femoral component  390  is more distal than the lateral side  396 . 
     Similarly,  FIG. 52  depicts a PFJ/condyle component  398  including a PFJ area  400  and a condyle area  402 . PFJ/condyle component  398  in this embodiment is stepped. In accordance with the present invention, even when PFJ/condyle component  398  is implanted, additional components may easily be added at later times. By way of example,  FIG. 52  shows a stepped condyle component  404  that may be implanted at a later (or earlier) date than PFJ/condyle component  398 . Moreover, the condyle area  402  of the PFJ/condyle component  398  and the condyle component  404  may be of different sizes. Also, as discussed below, the PFJ/condyle component  398  and the condyle component  404  may have different radii of curvature. 
     The present invention further provides latitude in optimizing the tibial components for specific patient conditions such as irregular bone geometries for earlier or later implanted components. As shown in  FIG. 52 , the tibial component inserts  406  and  408  may be implanted at any time before or after the implantation of the femoral components  400  and  404 . The tibial component inserts  406  and  408  may advantageously be fixed or meniscal bearing implants. The present invention further provides for individual optimization of the size of the tibial component inserts  406  and  408 , irrespective of the size of the other insert or of the femoral components. This allows a surgeon to optimize conformity between the femoral and tibial components while reducing inventory costs. 
     Condylar Variations 
     The present invention includes configurations for a variety of condyle geometries.  FIG. 53  depicts a femoral component  410  with condyle areas  412  and  414 . Condyle areas  412  and  414  in this embodiment are non-divergent.  FIG. 54  shows femoral component  416  with medial condyle area  418  and lateral condyle area  420 . Condyle areas  418  and  420  in this embodiment are divergent. In addition, the condyle areas may be designed to diverge equally (distance “A” of FIG.  54 =distance “B” of  FIG. 54 ), or one condyle area may diverge more than the other condyle area (distance “A” of FIG.  54 &gt;distance “B” of  FIG. 54 ). In the embodiment of  FIG. 54 , the medial condyle area  418  is also wider than lateral condyle area  420  (distance “C” of FIG.  54 &lt;distance “D” of  FIG. 54 ). Alternatively, condyle areas could be made to be equal (distance “D” of FIG.  54 =distance “C” of  FIG. 54 ). 
       FIG. 55  depicts the femoral component  422  and tibial component  424  of a knee replacement wherein the femoral component  422  has an asymmetry. More specifically, lateral condyle area  426  has a larger radius than medial condyle area  428 . This is shown more clearly in  FIG. 56  and  FIG. 57 . 
       FIG. 56  is a cross-sectional view of medial condyle area  428  of femoral component  422 , taken along line A-A.  FIG. 56  depicts a number of radii of curvature r 1  from a central point to the inner surface of medial condyle area  428 .  FIG. 57  is a cross-sectional view of lateral condyle area  426  of femoral component  422 , taken along line B-B.  FIG. 57  depicts a number of radii of curvature r 2  from a central point to the inner surface of lateral condyle area  426 . Comparison of the medial radii r 1  to lateral radii r 2  shows that the radius of curvature of the medial condyle area  428  is smaller than the radius of curvature of the lateral condyle area  426  (in general, r 1  is less than r 2 ). 
     Similarly, the radius of curvature in the plane orthogonal to the cross-sections of  FIG. 56  and  FIG. 57  may vary.  FIG. 58  depicts femoral component  430  which comprises lateral condyle area  432  and medial condyle area  434  wherein the femoral component  430  has an asymmetry in this orthogonal plane, that is, from side to side of the respective condyle areas. This is shown more clearly in  FIG. 59  and  FIG. 60 . 
       FIG. 59  is a cross-sectional view of medial condyle area  434  of femoral component  430  taken along line A-A of  FIG. 58 .  FIG. 59  depicts the radius of curvature r 1  from side to side of medial condyle area  434 .  FIG. 60  is a cross-sectional view of lateral condyle area  432  of femoral component  430 , taken along line B-B of  FIG. 58 .  FIG. 60  depicts the radius of curvature r 2  from side to side of lateral condyle area  432 . Comparison of the medial radius r 1  to lateral radius r 2  shows that the radius of curvature of the medial condyle area  434  is less than that of the lateral condyle area  432  (r 1  is less than r 2 ). 
     It should be further noted that the radius of curvature at different cross-sections of each condyle area from the anterior to the posterior of the condyle area may vary.  FIG. 61  shows a femoral component  436  that varies in such a manner. The cross-sections and radius of curvature for line A-A of  FIG. 58  at a posterior portion  438  of the femoral component  436  and line B-B of  FIG. 58  at a more anterior portion  440  of the femoral component  436  are shown in  FIGS. 62  and  63 , respectively. Comparison of the radii shows that the radius r 3  of the posterior portion  438  is smaller than the radius r 4  of the anterior portion  440 . 
     An alternative to providing components with geometries specifically adapted to a particular condyle in accordance with the present invention is to adapt the position and orientation of a single component to the particular geometry of the condyle. This is explained with reference to  FIGS. 64 ,  65  and  66 .  FIG. 64  shows a femur  442  with a PFJ component  444  and a condylar component  446  implanted on the lateral condyle of the femur  442 . The PFJ component  444  includes a medial node  445 . The track of the patella across the femur  442  as the leg goes from extension to flexion is indicated by patellar track  448 . The track of the tibia across the femur  442  as the leg goes from extension to flexion is indicated by tibial track  450 . The condylar component  446  is positioned such that the tibial track  450  lies along the longest portion of the condylar component  446 . 
       FIG. 65  shows a femur  452  with a PFJ component  454  and a condylar component  456 , which is identical to the condylar component  446 , implanted on the medial condyle of femur  452 . The PFJ component  454  is identical to the PFJ component  444  except that the PFJ component  454  includes both a medial node  455  and a lateral node  457 . The track of the patella across the femur  452  as the leg goes from extension to flexion is indicated by the patellar track  458 . The track of the tibia across the femur  452  as the leg goes from extension to flexion is indicated by the tibial track  460 . The condylar component  456  is positioned such that the tibial track  460  lies along the longest portion of the condylar component  456 . 
     The PFJ area of the femur  452  is, for purposes of this example, identical to the PFJ area of the femur  442 . Moreover, the patella track  448  and the patella track  458  are identically oriented on the respective femurs. Thus, because the PFJ components  444  and  454  are identical components, with the exception of the absence of a lateral node on the PFJ component  444 , they have been implanted in identical positions on the femurs  442  and  452 . However, the medial condyle of the femur  442  is lower than the medial condyle of the femur  452 . Additionally, the tibial track  456  is skewed when compared with the tibial track  446 . This is shown more clearly in  FIG. 66 . 
       FIG. 66  is an overlay of the components of  FIGS. 64 and 65  on the femur  452 .  FIG. 66  thus shows the femur  452 , the PFJ component  454 , the condylar component  456  and the patella track  460  of  FIG. 65 . Under the conditions set forth above, juxtaposition of the components of  FIG. 64  on  FIG. 66 , results in the PFJ component  444  aligning exactly with the PFJ component  454  with the exception of the lack of a lateral node on the PFJ component  444 . This is indicated in  FIG. 66  by the dashed reference line  444 . 
       FIG. 66  further shows the position of condylar component  446  and the tibial track  450  with the same alignment with the PFJ component  444  as shown in  FIG. 64 . However, even though the condylar component  456  is identical to the condylar component  446 ,  FIG. 66  shows that the condylar component  456  is positioned closer to the PFJ component  454  than the condylar component  446  is positioned to the PFJ component  456 . Additionally, the condylar component  456  is rotated in a slightly counter-clockwise direction compared to the condylar component  446 . 
     Thus, in accordance with the present invention, the position and orientation of a component on a femur may be adapted to optimize the performance of the component on the femur. Moreover, while the above discussion of condyle geometries used examples of condyle areas within certain unibody components, the geometries may be practiced with condyle components as well as components having condylar areas. 
     Unibody Femoral Component 
     While it is generally beneficial to use smaller components during replacement surgery, there may be instances where a full unibody femoral component is desired to be implanted.  FIG. 67  shows a femoral component  462  which comprises a PFJ area  464 , a medial area  466  and a lateral area  468 . 
     In accordance with the present invention, the femoral component  462  may include a variety of internal geometries.  FIG. 68  shows the femoral component  462  with a faceted interior in the anterior to posterior direction comprising flat surfaces  470 ,  472 ,  474 ,  476  and  478 .  FIG. 69  shows the femoral component  462 ′ with a curved interior surface  480 .  FIG. 70  shows the femoral component  462 ″ with a combined curved and flat interior comprising flat surface  482  and curved surface  484 . 
     Moreover, the interior surfaces of the femoral component  462  may be constructed with a variety of geometries in the medial to lateral direction. By way of example, but not of limitation,  FIG. 71A  shows a flat cross-section  486  taken across line A-A of  FIG. 68 ,  69  or  70 .  FIG. 71B  shows a curved interior  488  while  FIG. 71C  shows a faceted interior  490 .  FIG. 71D  shows an interior  492  with curved sides and a flat bottom while  FIG. 71E  shows an interior  494  with flat sides and a curved bottom. These shapes accommodate local bone geometry better than previous known shapes and enable the surgeon to leave more healthy bone in the joint. 
     As understood from the above descriptions and accompanying drawings, the system of the present invention provides a total or bi-compartmental knee comprised of components that may be implanted with six degrees of freedom. Specifically, with reference to the PFJ/medial condyle component  496  as shown in  FIG. 72 , a condylar component  498  may be moved upwardly, downwardly, to the left, to the right, or rotated to the left or to the right. Consequently, different patient geometries may be addressed without requiring a different component geometry for every possible patient geometry or requiring that the surgeon conform the bone to a component geometry by removing healthy bone. Instead, the surgeon may select a slightly different place of implantation or component orientation to accommodate patient bone geometry. 
     Exemplary Methods 
     One advantage of the system described herein is that it allows the surgeon to build a custom implant for each patient. Currently, implant systems are offered in a limited number of discrete sizes that most likely will not be precisely the size needed for a patient. For example, a patient&#39;s knee may measure 75-mm. However, available implants for this patient may measure 70-mm and 80-mm. 
     The surgeon in these instances typically uses a single cutting block that is designed for the replacement component. The cutting block is placed either against the posterior of the femur or against the anterior of the femur and provides guides for making four resections of the femur, two resections on the posterior side and two resections on the anterior side. Accordingly, the surgeon must choose to optimize the cuts either for the anterior fit or posterior fit of the component, or to split the misfit. 
     In any event, the surgeon has to choose between an implant that is too small or too big. This can adversely affect that outcome of the procedure. The implant system described in this invention would allow the surgeon to build an implant that is exactly 75-mm. Also, the surgeon can do this without having the added expense of a large inventory that includes many sizes. 
     In order to perform a custom implant in accordance with principles of the present invention, a surgeon first decides which areas of bone will be replaced. For purposes of this example, the anterior, posterior and distal portions of the femur will be resected. Accordingly, the surgeon makes a first cut in the distal end of a femur. Next, as shown in  FIG. 73 , a surgeon locates a first cutting block  500  adjacent to the resected distal end  502  and the posterior portion  504  of the femur  506 . The cutting block  500  comprises cutting guides  508  and  510 , which ensure that the resected posterior sections of the femur  506  will match the dimensions of a component  512  shown in  FIG. 74 . More specifically, the shaded portion  514  of the femur  506  will match shaded portion  516  of the component  512 . The shaded portion  514  of the femur  506  is then resected. Thus, the locations of the cuts at the posterior area of the femur  506  are determined as a function of the posterior boundary of the femur  506 . Accordingly, when the component  512  is attached to the femur  506 , the outer boundary of the component  512  will mimic the natural outer boundary of the posterior of the femur  506 . 
     The surgeon then places a second cutting block  518  in position to resect the anterior portion  520  of the femur  506  as shown in  FIG. 75 . The cutting block  518  includes the cutting guides  522  and  524 , which ensure the resected anterior areas of the femur  506  will match the dimensions of the component  526  shown in  FIG. 74 . More specifically, the shaded portion  528  of the femur  506  will match the shaded portion  530  of the component  526 . The anterior sections of the femur  506  are then cut, leaving the femur  506  in the configuration depicted in  FIG. 76 . Thus, the locations of the cuts of the anterior area of the femur  506  are determined as a function of the anterior boundary of the femur  506 . Accordingly, when the component  526  is attached to the femur  506 , the outer boundary of the component  526  will mimic the natural outer boundary of the anterior of the femur  506 . 
     Next, the width of the femur from point A to point B (see  FIG. 76 ) is measured and retained for future use. This measurement is called the anterior-posterior (AP) measurement. The bone is then prepared to receive the component  512  and the component  526  by boring hole  532  and another hole (not shown). Next, the component  512  and the component  526  are placed in position abutting the femur  506  as shown in  FIG. 77 , and screws  534 ,  536 , and two other similar screws (not shown) are inserted and torqued. The screws  534  and  536  and the two other screws are torqued until the AP measurement, the distance from point A to point B in  FIG. 77 , measures about 0.001 to 0.5 inches less than the initial AP measurement. This ensures that a good press fit of the implants will be realized while closely mimicking the size of the femur  506  prior to resection. 
     Once the components have been properly torqued, thereby clamping the femur  506  between the component  512  and the component  526 , a gap  538  between the components  512  and  526  may remain. The gap  538  represents the difference in the diameter of the femur  506  and the combined diameter of the components  512  and  526 . Accordingly, the present method allows for the outer boundary of replacement components to mimic the outer diameter of the natural bone even for irregular diameters. In accordance with the present invention, the components  512  and  526  may be configured such that the gap  538  is not located on a load line. If desired, the surgeon may fill this gap with an acceptable material such as materials herein described with respect to bone tides. 
     Accordingly, by providing a plurality of cutting blocks, each block optimized for particular components, and by using components such as components  512  and  526 , a custom fit may be realized for a patient, regardless of the patient&#39;s knee size. Thus, in accordance with the systems and methods of the present invention the size of the implanted components may be customized. Moreover, the plurality of cutting blocks may each provide for bone preparation to fit components having different internal geometries. Thus, the surgeon has additional freedom in optimizing each resection for a particular patient. Moreover, by using components such as components  512  and  526 , the femoral components may be clamped to the bone, thereby providing improved fixation of the components to the bone. 
     In accordance with an alternative method, a femur is prepared to receive an implant by making a series of parallel cuts in the femur. Typically, a bone is prepared by locating a box on the bone, and a guide is selected and positioned with in the box. The guide is configured to fit within the box at a certain distance from the side of the box. A number of guides are available for use in the box, each guide configured to fit within the box at a distance from the side of the box different from the other guides. Thus, a guide is selected based upon the amount of the bone that is to be resected. After the resection is made, the box is moved to provide another cut. 
     However, in accordance with one embodiment of the present method, a second parallel cut is made using a second guide prior to moving the box. This is beneficial in that once the box is positioned, making additional cuts parallel to the first cut is easily accomplished by simply using additional guides. 
     This method is enabled by the provision of replacement components with multiple parallel inner surfaces. Two such components are shown in  FIG. 78 . The PFJ  540  and the unicondylar component  542  are shown as they would be positioned when implanted on a femur (not shown). The PFJ component  540  includes the inner surfaces  544 ,  546  and  548 . The unicondylar component  542  includes the inner surfaces  550 ,  552 ,  554  and  556 . In this embodiment, the inner surfaces  544 ,  546  and  548  of PFJ  540  are parallel to inner surfaces  550 ,  556  and  554 , respectively, of unicondylar component  542 . Thus, for example, when the box is positioned to make a cut in the femur that will fit with inner surface  544 , by using a second guide, the cut in the femur that will fit with inner surface  550  may also be made without moving the box. 
     In accordance with a further method, a femoral prosthesis system is incrementally implanted into a femur of a patient over a number of spaced apart surgical procedures. With reference to  FIG. 79A , during a first surgical procedure, an incision  551  is made in the leg  553  of a patient. As shown in  FIG. 79B , the femur  555  of the patient includes a diseased portion  557  that is located generally in the patellofemoral joint area  559  of the femur  555 . Accordingly, during the first surgical procedure, the diseased portion  557  is resected, along with a minimal amount of healthy bone. Next, a replacement patellofemoral joint component  561  is advanced through the incision  551  and implanted into the resected area of the patellofemoral joint as shown in  FIG. 79C . The incision  551  is then closed as shown in  FIG. 79D . 
     During a second surgical procedure, an incision  563  is made in the same leg  553  of the same patient as shown in  FIG. 79E . The incision  563  is made in this example on the opposite side of the leg  553  as the incision  551  so as to allow access to the diseased portion  565  of the medial condyle  567  shown in  FIG. 79F . After the diseased portion  565  is resected, along with a minimal amount of healthy bone in the medial condyle  567 , a replacement medial condyle component  569  is implanted in the medial condyle  567  as shown in  FIG. 79G . 
     In accordance with principles of the present invention, the medial condyle component  569  is implanted in the medial condyle  567  adjacent to, but spaced apart from, the patellofemoral component  561 . Alternatively, the medial condyle component  569  may be implanted in the medial condyle  567  adjacent to and abutting the patellofemoral component  561 . In either event, spacers, which may be integral to the components, may be used to reduce the production of wear debris and removal or replacement of the patellofemoral component  561  is not required. 
     Those of ordinary skill in the art will appreciate that the foregoing procedures may be reversed such that the condylar component is implanted in the first procedure and the patellofemoral joint component is implanted in the second procedure. Moreover, additional components may be implanted either in conjunction with the foregoing procedures or during procedures either before or after the foregoing procedures. Thus, in accordance with principles of the present invention, a surgeon need only replace the diseased portion of a femur. Furthermore, in the event another portion of the femur becomes diseased at a later time, the newly diseased portion may be replaced without removing the previously implanted component. 
     In a further embodiment, the prosthesis system is assembled ex vivo and then implanted as a unit. In accordance with this method, an incision  900  is made in a leg  902  as shown in  FIG. 80A . The incision  900  exposes the femur  904  shown in  FIG. 80B . After making any desired measurements, the portion of the femur  904  to be resected is determined and the placement of the cuts is determined as indicated by the dashed line  906 . The femur  904  is then resected resulting in the configuration shown in  FIG. 80C . 
     In conjunction with the determination of the portion of the femur  904  to be resected, a PFJ component  908  (see  FIG. 80D ) is selected, preferably from a kit comprising a variety of PFJ components of varying dimensions. The PFJ component  908  includes an outer articulating surface  910 , an inner bone mounting surface  912  and a side  914  that includes a connector receptacle (not shown). The PFJ component  908  is selected to closely approximate the geometry of the PFJ portion of the femur  904  in a healthy state. 
     A condylar component  916  having an outer articulating surface  918 , an inner bone mounting surface  920  and a side  922  that includes a connector receptacle (not shown) and a resilient connector  924  are further selected. In this example, the resilient connector  924  includes an integrally formed spacer  926 . 
     The PFJ component  908  and the condylar component  916  are then connected using the resilient connector  924  such as by insertion of the resilient connector  924  into the connector receptacles (not shown) in the side  914  of the PFJ component  908  and the side  922  of the condylar component  916 . The connection of the PFJ component  908  and the condylar component  910  results in the prosthesis system  928  shown in  FIG. 80E . In the prosthesis system  928 , the PFJ component  908  is resiliently connected to, but spaced apart from, the condylar component  916  by the resilient connector  924 . 
     The prosthesis system  928  is then inserted through the incision  900  and mounted onto the femur  904 . Accordingly, as shown in  FIG. 80F , the bone mounting surface  912  of the PFJ component  908  and the bone mounting surface  920  of the condylar component  916  are mounted on the femur  904 . Additionally, the side  914  of the PFJ component  908  is in opposition to the side  922  of the condylar component  916 . Because of the spacer  926  on the resilient connector  924 , however, a gap, generally indicated by the arrow  930 , exists between the adjacent PFJ component  908  and condylar component  916 . The gap may be filled with any acceptable filler material such as bone was or bone cement. The method ends with the closing of the incision  900  as shown in  FIG. 80G . 
     Guides and Instruments 
     Traditionally, bone preparation for a total or partial knee prosthesis has relied upon the use of the above discussed box and guides along with an oscillating saw and blade. Thus, a surgeon presented with a defective area  558  shown in  FIG. 81 , would traditionally make a cut on the femur  560  as indicated by the dashed line  562 , resecting the entire anterior portion of the condyle  564 . For traditional replacement components, this approach to resection is very effective. However, such an approach results in a large resection of healthy sections of bone. 
     In order to provide more flexibility than available with traditional tools, there has recently developed a trend to use other types of instruments in removing bone. Such tools include hi-speed burrs, rasps, osteotomes and routers. The increased flexibility provided by these newly used tools includes the ability to limit surgical resection to only those areas of the bone that actually need to be replaced. Thus, with reference to  FIG. 81 , resection of femur  560  may be limited to defective area  558  and a minor amount of healthy bone. This ability is complimentary to the various components described above, as the resection of bone can be limited to an area that corresponds to a selected component. 
     The present invention includes a number of guides that may be used to assist in performing such resection. One such guide is shown in  FIG. 82A . The guide  566  includes a pin  568 , a guide surface  570  and a tide mark  572 . The pin  568  is used to anchor the guide  566  in a bone. Positioning of the guide  566  within a bone may be done using computer aided surgery. The tide mark  572  is used to indicate the depth to which the guide  566  is to be inserted into the bone. The tide mark  572 , which may be erasable, may be determined using computer aided modeling. Referring now to  FIG. 82B , the guide surface  570  is generally sized and contoured to match the curvature and general shape of a replacement component such as the component  574  shown in  FIG. 82C . 
     Exemplary use of the guide  566  is explained with reference to  FIG. 81 . Initially, the defective area  558  and the femur  560  are modeled. Based upon this modeling, it is determined that the replacement component  574  is slightly larger than the defective area  558  and matches the general contour of the femur  560  in the vicinity of the defective area  558 . Thus, the guide  566 , which correlates with the component  574 , is identified as the appropriate guide to be used. Accordingly, the location of the tide mark  572  on the guide  566  is determined as a function of the thickness of the component  574 . The system will further identify, in this embodiment, a burr head size to be used with the guide  566 . 
     After marking the guide  566  with the tide mark  572 , the guide  566  is inserted into the femur  560  as shown in  FIG. 83 . Placement of the guide  566  into the femur  560  may be computer aided. The burr head identified for use, such as burr head  576  shown in  FIG. 84 , is inserted into a hi-speed burr tool  578 . The hi-speed burr tool  578  includes a guide surface rest  580  and a roller  582 . The hi-speed burr tool  578  is then energized and the guide surface rest  580  is placed on the guide surface  570  with the roller  582  on the side of the guide  566 . The surgeon then guides the hi-speed burr tool  578  around the periphery of the guide  566 , as indicated by the arrows  584  in  FIG. 85 , creating a channel  586  in the femur  560  around the defective area  558  as shown in  FIG. 83 . The channel  586  may be made in one continuous cut or in a series of cuts. The surgeon then removes the guide  566 , and excises the bone within the area defined by the channel  586  to the depth of the channel  586 . 
     As stated above, the guide  566  is generally in the shape of the replacement component  574 . Thus, selection of a burr head of an appropriate size results in the outer wall of the channel  586  conforming to the size and shape of the replacement component  574  while completely excising the outer boundaries of the defective area  558 . Moreover, the depth of the resection is determined by the insertion of the guide  566  to the depth of the tide mark  572  and the height of guide surface rest  580  above the bottom of burr head  576 . Thus, the depth of the resection may be established to coincide with the thickness of the replacement component  574 . 
     By providing burr heads of different sizes, a single guide may be used with different replacement components of different widths and heights. Alternatively, the standoff distance between the edge of the roller  582  of the hi-speed burr tool  578  and the outer periphery of the burr head  576  may be variable to accomplish the same functionality. Similarly, the height of the guide surface rest  580  may be adjustable to provide resection of different depths. The instrument may also be configured as a side cutting instrument such as the side cutting tool  588  shown in  FIG. 86 . The side cutting tool  588  includes a channel  590  which is configured to accept the guide surface  592 . In some embodiments, the guide surface  592  is in the form of a continuous ridge about the periphery of a guide. 
     Those of ordinary skill in the relevant art will appreciate that the outer perimeter of the guide surface may be formed in a variety of shapes to accommodate replacement components of various shapes. Additionally, the outer perimeter may include curvature in multiple axes to provide, for example, for use on the ball shaped area of a bone. These and other permeations are within the scope of the present invention. 
     An alternative embodiment of a guide is shown in  FIG. 87 . The guide  594  is a punch guide. The guide  594  includes an outer cutting edge  596 , and a plurality of internal cutting edges  598 . For clarity of explanation,  FIG. 88  shows the guide  594  with the internal cutting edges  598  removed. The outer cutting edge  596  is shaped to conform to the outer shape of a replacement component. The height of the outer cutting edge  596  conforms to the thickness of the replacement component. Each of the internal cutting edges  598  may be separately shaped and sized to conform to internal contours and thicknesses of the replacement component. Thus, when forced against a bone, the outer cutting edge  596  and each of the internal cutting edges  598  cut into the bone. The guide  594  may then be removed, leaving a series of cuts in the bone that conform to the shape, contour and thickness of the replacement component. By using a tool to excise the bone down to the level of the cuts, a bone can be resected to receive the replacement component. In an alternative embodiment, a guide only includes the outer cutting edge  596 . 
     Placement of a punch guide may be facilitated according to a variety of alternative methods. One method uses the device shown in  FIG. 89 . The guide  600  includes a cutting edge  602  around the periphery of the guide  600  and guide holes  604  and  606 . The guide  600  may further include internal cutting edges. The guide  600  is shown inserted onto pins  608  and  610  which extend through the holes  604  and  606 , respectively. In practice, the pins  608  and  610  are inserted into a bone. The guide  600  is then positioned over the pins  608  and  610  aligning the holes  604  and  606  with the pins  608  and  610 . The guide  600  is then moved against the bone. Thus, the guide  600  is located in the desired position. The method using the guide  600  may then proceed in a manner similar to that described in reference to the guide  594 . 
     The depth of the cut made by the guide  600  may be established in a number of ways. For example, the depth of the cut may be established by the depth of the cutting edge  602 , by marking the desired depth on the cutting edge  602 , by a tide mark on the pins  608  and  610 , or by providing stops on the pins  608  and  610  beyond which the guide  600  cannot be moved. Placement of the pins  608  and  610  may be accomplished using computer aided surgery or other imagery assisted techniques to ensure proper depth and location of the cut. 
     Alternatively, a previously implanted component whose position on a femur is known may be used along with a pin guide to place the pins that are used to align a guide. Such a pin guide is discussed in reference to  FIG. 90 , wherein a unitrial component  612  is implanted in the femur  614 . The unitrial component  612  includes the holes  616  and  618 . 
     A pin guide  620  is also shown in  FIG. 90 . In this embodiment, the pin guide  620  includes a swing arm  622 , a base arm  624  and pin guide holes  626  and  628 . The base arm  624  is configured to be inserted into the hole  616  of the unitrial component  612 . Moreover, the base arm  624  and the hole  616  are configured to provide a known orientation of the base arm  624  with respect to the orientation of the unitrial component  612 . Such a configuration may include a key-lock configuration or simply a mark on the base arm  624  that is aligned with a mark on the unitrial component  612 . The base arm  624  may further be adjustable in height so as to account for curvature of the bone. 
     A mechanism is also provided for establishing a desired orientation of the swing arm  622  with respect to the base arm  624 . This may be a reference mark on one arm and a sequence of numbers on the other arm. Accordingly, a precise orientation of the pin guide  620  with respect to the femur  614  is achieved. 
     Specifically, modeling of the femur  614  provides the geometry of the femur  614 . Imagery and subsequent modeling of the unitrial  612  provides the exact location of the hole  616  with respect to the femur  614 . Because the height and orientation of the base arm  624  is known, and because the length and orientation of the swing arm  6622  is known, the precise location of the pin guide  620  with respect to the femur  614  is known. Therefore, pins may be precisely inserted into the femur  614  through the pin guide holes  626  and  628 . 
     Alternatively, a temporary component may be placed on the femur  614  prior to any resection of the femur  614 . In this alternative method of the present invention, the temporary component is imaged once it is placed. Thus, the guide pin placement, for either or both of the PFJ or condylar components, may be guided by a temporary component in a manner similar to the above described placement of the PFJ guide pins. Those of ordinary skill in the relevant art will appreciate that any number of component guide pins may be placed using this method. 
     Certain instruments are very useful for making cuts into the planar surface of a bone. By way of example, the saw  630  shown in  FIG. 91  includes an abrasive tip  632  connected to a shaft  634 . Two guide studs  636  and  638  are located on the housing  640  of the saw  630 . The shaft  634  moves from side to side (up and down as viewed in  FIG. 91 ). The axes  642  and  644  show the outer limits of the arc swept by the shaft  634  through each cycle of motion. 
     Accordingly, when moving the saw  630  in a direction perpendicular to the axis of the housing  640 , such as in the direction of the arrow  646 , bone may only be cut to the depth indicated by dimension A-A with a single pass over the bone. This is referred to herein as “pass depth”. The pass depth may be adjusted by providing abrasive heads of different sizes since longer heads sweep a larger arc. Moreover, a saw may be oriented to cut along the direction of travel or orthogonal to the direction of travel. Thus, a single abrasive head may provide for resections of two different widths depending upon the configuration of the abrasive head within the saw. 
     The saw  630  may be used with the guide  648  shown in  FIG. 92  to make cuts of a specific depth into a bone, including depths greater than a single pass depth. The guide  648  comprises a channel  650 . The channel  650  is generally serpentine, consisting in this embodiment of generally parallel sub-channels  652 ,  654  and  656 . The sub-channels  652 ,  654  and  656  are spaced apart at a distance up to the pass depth of the saw  630  with a particular abrasive head. The sub-channel  652  is joined to the sub-channel  654  by an end channel  658  and the sub-channel  654  is joined to the sub-channel  656  by an end channel  660 . Accordingly, the channel  650  is continuous from the channel entry  662  to the channel stop  664 . 
     Operation of the saw  630  with the guide  648  begins by identifying the area of a bone to be resected. An abrasive tip for the saw  630  is then selected. Once the abrasive head is selected, the pass depth is known, and the appropriate guide  648  may be selected. 
     It is contemplated within the scope of the present invention to provide a kit of sub-channels and curves that may be used to construct specific guides for use with specific resections. When performing this method with the aid of a computer program, the program may be designed to generate the design of the guide. In any event, once pass depth is known, guide sub-channel separation may be determined. Guide channel separation is selected such that the distance between adjacent sub-channels of the guide is not greater than the pass depth of the abrasive head. In one embodiment, the sub-channel separation is a function of the thickness of the wall of the guide separating adjacent sub-channels. 
     The kit may thus provide a plurality of sub-channel components that may be attached one to another. The sub-channel components may include a plurality of geometries to be used for various areas of a bone. Thus, curved sub-channel sections may be used for resection about the head of a femur, while relatively straight sub-channels may be used for resections limited to one area of a condyle. A computer program may be used to identify the sub-channels and curves to be used and the configuration of the components of the guide based upon modeling of the bone and the area to be resected. 
     Once the guide  648  is assembled or selected, it is attached to the bone to be resected with the channel entry  662  oriented away from the bone to be resected. The guide  648  is located at a height above the bone such that when the guide studs  636  and  638  are within the sub-channel  652  and against the wall of the sub-channel  652  closest to the bone, the abrasive tip will extend into the bone by the distance of one pass depth or less. Attachment of the guide  648  to the bone may be accomplished by use of a clamp, and placement of the guide  648  may be accomplished by computer guided surgery. 
     The guide studs  636  and  638  are then inserted into the channel entry  662  and the saw  630  is energized. The surgeon then moves the saw  630  along the channel  650 , through the sub-channel  652 . When both of the guide studs  636  and  638  are within the end channel  658 , the saw  630  can be lowered to the sub-channel  654  and another pass made over the area to be resected. 
     If the area to be resected is wider than the cut possible with the saw  630 , a second guide may be used adjacent the guide  648  or the guide  648  may be relocated for a second set of passes over the bone. 
       FIG. 93  shows an alternative embodiment of a guide for use with a saw that has guide pins on opposing sides of the housing of the saw. The guide  666  includes a channel  668  that is curved, in this embodiment, to conform to the lower surface of a femur  670 . The guide  666  further comprises a channel  672 , shown in  FIG. 94 . The channels  668  and  672  are located on either side of a cavity  674 . Accordingly, to use the guide  666 , the opposing guide pins of a saw are inserted into the channels  668  and  672 , respectively, and the abrasive tip and the saw are inserted through the opening of the cavity  674 . 
     In one embodiment, the channels  668  and  672  are configured identically to provide a uniform cut. However, if desired, the lengths and separation of the sub-channels may be selected to provide cuts that vary in shape or depth from one side of the cut to the other side of the cut. 
     A wire saw that may be used with guides incorporating features of the present invention is shown in  FIG. 95 . The saw  676  includes a handle (not shown), a guide platform  678 , a guide pin  680  and a wire  682 . The saw  676  may further include a means for moving the wire  682  such as a reciprocating means or a rotating means. The saw  676  may be used with the guide  684  shown attached to a femur  686  in  FIG. 96 . The guide  684  includes a channel  688  and a channel  690  shown in  FIG. 97 . 
     In operation, the guide pin  680  is inserted into the channels  688  and  690  and the guide platform  678  rests on top of the channels  688  and  690 . This is shown more clearly in  FIG. 98 . The relatively broad base of the guide platform  678  resting on the generally parallel channels  688  and  690  ensures that the wire  682  remains perpendicular to the channels  688  and  690  during the resection. The surgeon then cuts the bone by moving the saw  676  along the channels  688  and  690 . As the saw  676  is moved, the guide pin  680  constrained by the channels  688  and  690  and the guide platform  678  resting on the generally parallel channels  688  and  690  maintains the wire  682  within the femur  686  at the desired location. The use of the guide  684  results in a smoothly curved resected surface, shown as the dashed line  692  in  FIG. 96 . 
     Other bone surface geometries may be obtained using the principles of the present invention. By way of example, but not of limitation, the saw  676  may be used with the guide  694  shown in  FIG. 99 . The channel  696  of the guide  694  comprises a plurality of linear segments. Accordingly, use of the guide  694  results in faceted resection of the femur  698  as indicated by the dashed line  700 . This embodiment and others are within the scope of the present invention. 
     Those of ordinary skill in the art will recognize that the above-described system may be used in a significant number of widely varying procedures. The preceding describes one fairly simple method for incorporating the system of the present invention in a knee replacement surgery in order to show one advantage of the present invention. Those of ordinary skill in the art will appreciate that a number of alternative methods are enabled by the present invention, those alternative methods being within the scope of the present invention. 
     While the present invention has been illustrated by the description of exemplary processes and system components, and while the various processes and components have been described in considerable detail, applicant does not intend to restrict or in any limit the scope of the appended claims to such detail. Additional advantages and modifications will also readily appear to those ordinarily skilled in the art. The invention in its broadest aspects is therefore not limited to the specific details, implementations, or illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept. By way of example, but not of limitation, the system described herein may be applied to other bones and joints besides the knee, even joints with a single articulating compartment. Such bones may include tibial and humerus bones.