Abstract:
Methods and devices for correcting wear pattern defects in joints. The methods and devices described herein allow for the restoration of correcting abnormal biomechanical loading conditions in a joint brought on by wear pattern defects, and also can, in embodiments, permit correction of proper kinematic movement.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 14/222,836 filed Mar. 24, 2014 and entitled “Implants for Altering Wear Patterns of Articular Surfaces,” which in turn is a divisional of U.S. application Ser. No. 12/398,598 filed Mar. 5, 2009 and entitled “Implants for Altering Wear Patterns of Articular Surfaces,” which in turn claims priority to U.S. Provisional Application 61/034,035 filed Mar. 5, 2008 and entitled “Wear Pattern-Optimized Articular Implants.” Each of the above described applications is hereby incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The embodiments described herein relate to orthopedic methods, systems and devices. In particular, new methods, systems and devices for articular resurfacing in joints including the knee are provided. 
     BACKGROUND 
     There are various types of cartilage, e.g., hyaline, elastic and fibrocartilage. Hyaline cartilage is found at the articular surfaces of bones, e.g., in the joints, and is responsible for providing the smooth gliding motion characteristic of moveable joints. Articular cartilage is firmly attached to the underlying bones and measures typically less than 5 mm in thickness in human joints, with considerable variation depending on the joint and the site within the joint. 
     Adult cartilage has a limited ability of repair; thus, damage to cartilage produced by disease, such as rheumatoid and/or osteoarthritis, or trauma, can lead to serious physical deformity and debilitation. Furthermore, as human articular cartilage ages, its tensile properties change and the cartilage tends to wear away. The superficial zone of the knee articular cartilage exhibits an increase in tensile strength up to the third decade of life, after which it decreases markedly with age as detectable damage to type II collagen occurs at the articular surface. The deep zone cartilage also exhibits a progressive decrease in tensile strength with increasing age, although collagen content does not appear to decrease. These observations indicate that there are changes in mechanical and, hence, structural organization of cartilage with aging that, if sufficiently developed, can predispose cartilage to traumatic damage. 
     In osteoarthritis, human joints such as the knee, hip, ankle, foot joints, shoulder, elbow, wrist, hand joints, and spinal joints tend to wear away the articular cartilage. The wear is frequently not uniform, but localized to a defined region within a joint. For example, in a knee joint, the wear can be on a medial or lateral femoral condyle, a medial or lateral tibial plateau, a medial or lateral trochlea, a medial facet, lateral facet or median ridge of the patella. In a hip joint, the wear can be on an acetabulum or a femoral head or both. 
     Generally, wear can be limited to one articular surface or it can affect multiple articular surfaces. Wear can occur in one or more subregions on the same articular surface or multiple articular surfaces. 
     In a medial femoral condyle or medial tibial plateau, wear can occur in an anterior, central or posterior portion of the articular surface. Wear can also occur in a medial or lateral portion of an articular surface. In a lateral femoral condyle or lateral tibial plateau, wear can occur in an anterior, central or posterior portion of the articular surface. Wear can also occur in a medial or lateral portion of an articular surface. In a femoral head or acetabulum, wear can occur in an anterior, posterior, medial or lateral, superior or inferior location. 
     In short, any location of wear is possible, and any combination of wear patterns on the same articular surface and opposing articular surfaces is possible. 
     Wear starts typically in the articular cartilage, but it can then extend into the subchondral bone and marrow cavity. Wear can be accompanied by cartilage loss, subchondral sclerosis, subchondral cyst formation, osteophyte formation, bone marrow edema. 
     Wear is frequently the result of an abnormal biomechanical loading condition in a joint. While modern arthroplasty surgery attempts to correct such abnormal biomechanical loading conditions in a joint, some residual biomechanical loading abnormality or new biomechanical loading abnormality is frequently present after partial or total joint replacement surgery. 
     Abnormal biomechanical loading of joint implants is a frequent cause for implant failure since current implants cannot account for the increased loads and stresses resulting from such abnormal loading. 
     Usually, severe damage or cartilage loss is treated by replacement of the joint with a suitable prosthetic material, most frequently metal alloys. See, e.g., U.S. Pat. Nos. 6,383,228; 6,203,576; and 6,126,690. As can be appreciated, joint arthroplasties are highly invasive and require surgical resection of the entire (or a majority of) the articular surface of one or more bones involved in the repair. Typically with these procedures, the marrow space is fairly extensively reamed in order to fit the stem of the prosthesis within the bone. Reaming results in a loss of the patient&#39;s bone stock, and over time subsequent osteolysis will frequently lead to loosening of the prosthesis. Further, the area where the implant and the bone mate degrades over time requiring the prosthesis to eventually be replaced. Since the patient&#39;s bone stock is limited, the number of possible replacement surgeries is also limited for joint arthroplasty. In short, over the course of 15 to 20 years, and in some cases even shorter time periods, the patient can run out of therapeutic options ultimately resulting in a painful, nonfunctional joint. 
     SUMMARY 
     The embodiments described herein are directed to providing methods and devices for correcting wear pattern defects in joints. They provide for improved, and, in some embodiments, optimized or ideal, implant systems to correct or manage abnormal wear patterns. Some of the methods and devices described herein allow for the correction of abnormal biomechanical loading conditions in a joint brought on by wear pattern defects, and also can, in embodiments, permit correction of proper kinematic movement. Abnormal biomechanical loading of conventional joint implants is a frequent cause for implant failure, since current implant designs are unable to account for the increased loads and stresses resulting from such abnormal loading. Alternatively, the methods and devices described herein allow for the accommodation of abnormal biomechanical loading conditions in the shape of the implant system, thus reducing the forces on the implant that can lead to implant failure. 
     One embodiment is a method for designing an orthopedic device that alters a wear pattern on an articular surface of a joint. The method may include receiving image data associated with the joint, e.g., via a computer network; determining a wear pattern of an articular surface at least in part from the image data; and designing an orthopedic device based at least in part on the image data. The orthopedic device can be designed to alter the wear pattern of the articular surface to a revised wear pattern. 
     Other embodiments may include one or more of the following. The alteration may be a change to or an improvement over the existing wear pattern, or the wear pattern can be optimized to provide an ideal wear pattern. The image data may be derived from a technique selected from the group consisting of arthroscopy, arthrotomic examination, gait analysis, and imaging analysis; or a combination thereof. 
     The step of designing can include, for example, altering the wear pattern at least in part by adjusting the location of the wear pattern on the articular surface; altering the wear pattern at least in part by distributing the load that will be placed on the articular surface; or altering the wear pattern at least in part by reducing point loading on the articular surface. 
     The wear pattern can be determined automatically, semi-automatically, or manually. 
     The method can further include determining a second wear pattern of a second articular surface of the joint from the image data. The orthopedic device can be designed based at least in part on the image data associated with the second articular surface, and the orthopedic device can be designed to alter the second wear pattern of the second articular surface to a second revised wear pattern. The orthopedic device can be, for example, a bicompartmental resurfacing device for a knee. 
     A second wear pattern of a second articular surface of the joint can be determined from the image data. A second orthopedic device can be based at least in part on the image data associated with the second articular surface, and the second orthopedic device can be designed to alter the second wear pattern of the second articular surface to a second revised wear pattern. For example, the first orthopedic device can be a tibial tray for a knee and the second orthopedic device can be a second tibial tray for another compartment of the knee. 
     A second orthopedic device can be designed based at least in part on the image data, and it can be designed to alter the wear pattern of the articular surface to the revised wear pattern. For example, the first orthopedic device can be a tibial tray for a knee joint and the second orthopedic device can be a unicompartmental femoral resurfacing device for the knee joint. The two implants can be designed to be complimentary and thereby affect the alteration in the wear pattern as designed. 
     The orthopedic device can be many different types of devices such as a replacement hip joint or a knee replacement device including a femoral component and a tibial component. The orthopedic device can be designed using a library of design elements. 
     The orthopedic device can be designed to include at least one surface that conforms to an existing surface of the joint (see, e.g., U.S. patent application Ser. No. 10/997,407, filed Nov. 24, 2004, which is incorporated herein by reference in its entirety). The orthopedic device can be designed to include at least one surface that is derived from an existing surface of the joint. For example, the derived surface can exclude a defect of the existing surface, it can approximate an ideal surface of the joint, and it can approximate a healthy surface of the joint. Similarly, the orthopedic device can be designed to include at least one curve derived from an existing surface of the joint. For example, the curve can exclude a defect of the existing joint, it can approximate an ideal curve of the joint, and it can approximate a healthy surface of the joint. The orthopedic device also can be designed to include at least one dimension that is derived from an existing dimension of the joint. For example, the derived dimension can exclude a defect of the existing joint, it can approximate an ideal dimension of the joint, and it can approximate a dimension associated with a healthy joint. 
     The orthopedic device can be designed to be placed at least in part on cartilage associated with the joint, and it can be designed to be placed at least in part on subchondral bone associated with the joint. It can also be designed to be placed on other types of tissue or combinations of tissue. 
     The method can also include the production of the orthopedic device. For example, the orthopedic device can be produced using traditional methods such as casting or newer technologies, such as direct digital manufacturing. As an alternate example, the orthopedic device can be produced by tailoring a precursor orthopedic device, which may be, e.g., selected from a library of orthopedic devices. Similarly, the orthopedic device can be produced by altering a standard orthopedic device, which may be, e.g., selected from an inventory of orthopedic devices 
     Another embodiment is a method for preparing an implant for correcting an articular surface wear pattern that includes obtaining an image of an articular surface; analyzing the image for the presence or absence of wear pattern indicia; determining a wear pattern from the wear pattern indicia; and providing an implant having a characteristic topography for correcting the wear pattern. The implant can have an interior surface and an outer surface. The interior surface may be a mirror image of the articular surface. 
     An implant for correcting an articular surface wear pattern, comprising an implant body having a characteristic topography, an interior surface, and an outer surface, where the implant body topography is derived from a wear pattern analysis of the articular surface. The implant can include an interior surface is a mirror image of the articular surface. 
     Another embodiment is a method of joint arthroplasty that includes: obtaining an image of a surface of a joint; the surface of the joint including a wear pattern; deriving a shape of the joint surface based, at least in part, on the image; and providing an implant having a surface based on the surface of the joint. The implant can be configured to alter the wear pattern of the joint. 
     Other embodiments may include one or more of the following. Obtaining the image can include an imaging technique selected from the group consisting of x-ray imaging and processing; fluoroscopy; digital tomosynthesis; ultrasound; optical coherence, conventional, cone beam, or spiral computed tomography (CT); single photon emission tomography (SPECT); bone scan; positron emission tomography (PET); magnetic resonance imaging (MRI); thermal imaging; and optical imaging, or a combination thereof. The joint can be any joint with an articular surface, for example, a knee, a shoulder, a hip, a vertebrae, an elbow, an ankle, a foot, a toe, a hand, a wrist and a finger. The wear pattern can be based, at least in part, on one of a presence, absence, location, distribution, depth, area, or dimensions of cartilage loss; presence, absence, location, distribution, depth, area, or dimensions of subchondral cysts; presence, absence, location, distribution, depth, area, or dimensions of subchondral sclerosis; presence, absence, location, distribution, volume, area, depth or dimensions of a subchondral bone plate abnormality; presence, absence, location, distribution, or dimensions of a subchondral bone deformity; presence, absence, or severity of a varus or valgus deformity; presence, absence or severity of recurvatum or antecurvatum, and presence, absence, location, distribution, volume, depth or dimensions of bone marrow edema. The surface of the implant can be substantially at least one of rigid, non-pliable, non-flexible and non-resilient, and can be made of various suitable materials or combinations of materials, e.g., polymer, a cross-linked polymer, a ceramic, a metal, an alloy, and a ceramic-metal composite. 
     In another embodiment, a wear pattern is determined pre-operatively or intraoperatively. Wear patterns may be assessed by, e.g.: arthroscopy; arthrotomy; imaging tests such as x-ray imaging; fluoroscopy; digital tomosynthesis; cone beam, conventional and spiral CT; bone scan; SPECT scan; PET; MRI; thermal imaging; optical imaging; and any other current and future technique for detecting articular wear; optical coherence tomography; gait analysis; and techniques merging information from one or more of these tests. Many modifications and derivatives of these imaging tests can be used. For example, with MRI, images can be visually interpreted for assessing cartilage loss or bone deformity. Alternatively, computer methods including maps of cartilage thickness can be utilized for this purpose. Alternatively, a scan reflecting biomechanical composition of the articular cartilage can be performed. These include, but are not limited to, dGEMRIC, T1Rho, and T2 scans. 
     Different scanning methods within the same modalities and/or different modalities can be combined in order to determine one or more wear patterns. 
     In one embodiment, a wear pattern can be determined and an implant can be designed or selected that is adapted or optimized for a patient&#39;s wear pattern. Such adaptations or optimizations can include in the area of the wear pattern or areas adjacent to a wear pattern: decrease in material thickness; increase in material thickness; change in material composition; change in cross-linking properties, e.g., via local exposure to Gamma radiation or other cross-linking reagents; change in implant shape, e.g., change in convexity or concavity of one or more surface in one or more dimensions; enhanced matching of shape between two mating articular surfaces (enhanced constraint); decreased matching of shape between two mating articular surfaces (decreased constraint). 
     In one embodiment, an implant can be designed for a wear pattern measured in a patient. 
     In another embodiment, a wear pattern can be measured in a patient and an implant with a matching wear pattern design can be selected from a library of pre-manufactured implants. 
     In yet another embodiment, a wear pattern-specific implant shape or geometry is achieved using a number of manufacturing techniques, including, but not limited to: polishing; milling; machining; casting; rapid protocasting; laser sintering; laser melting, and electro abrasion. 
     In one embodiment, the wear pattern-adapted articular surface is formed de novo. In another embodiment, the wear pattern-adapted articular surface of the implant is achieved by processing an implant with a standard shape of the articular surface (a “blank”) and adapting the shape for a patients&#39; wear pattern, e.g., using machining or electro abrasion. 
     In another embodiment, methods for preparing an implant for correcting or accommodating an articular surface wear pattern are disclosed, wherein an image of an articular surface is obtained; the image is analyzed for the presence or absence of wear pattern indicia; a wear pattern is determined from the wear pattern indicia; and an implant with an inferior surface and a superior surface is provided, having a characteristic topography for correcting or accommodating the wear pattern. 
     In yet another embodiment, an implant is disclosed for correcting or accommodating an articular surface wear pattern, including an implant body having a characteristic topography, an inferior surface, and a superior surface, where the implant body topography is derived from a wear pattern analysis of the articular surface. 
     In another embodiment, a method of joint arthroplasty includes obtaining an image of a surface of a joint, the surface of the joint including a wear pattern. A shape of the joint surface is derived based, at least in part, on the image. An implant is provided having a surface that either conforms with or duplicates the surface of the joint. 
     In related embodiments, obtaining the image may include x-ray imaging and processing; fluoroscopy; digital tomosynthesis; ultrasound; optical coherence, conventional, cone beam, or spiral computed tomography (CT); single photon emission tomography (SPECT); bone scan; positron emission tomography (PET); magnetic resonance imaging (MRI); thermal imaging; or optical imaging, or a combination thereof. The joint may be a knee, shoulder, hip, vertebrae, elbow, ankle, foot, toe, hand, wrist or finger. The wear pattern may be determined based, at least in part, on: a presence, absence, location, distribution, depth, area, or dimensions of cartilage loss; presence, absence, location, distribution, depth, area, or dimensions of subchondral cysts; presence, absence, location, distribution, depth, area, or dimensions of subchondral sclerosis; presence, absence, location, distribution, volume, area, depth or dimensions of a subchondral bone plate abnormality; presence, absence, location, distribution, or dimensions of a subchondral bone deformity; presence, absence, or severity of a varus or valgus deformity; presence, absence or severity of recurvatum or antecurvatum, and/or presence, absence, location, distribution, volume, depth or dimensions of bone marrow edema. The surface of the implant may be substantially rigid, non-pliable, non-flexible and/or non-resilient. The surface of the implant may include a polymer, a cross-linked polymer, a ceramic, a metal, an alloy and/or a ceramic-metal composite. Providing the surface of the implant may include rapid prototyping, laser cutting, laser sintering, electron beam melting, casting and/or milling. The method may further include positioning the implant adjacent an implantation site. The surface of the implant may be shaped prior to positioning the implant adjacent the implantation site. 
     In accordance with another embodiment, an implant for joint arthroplasty includes an implant surface that either conforms to or duplicates a joint surface, the joint surface including a wear pattern. 
     In related embodiments, the implant surface may be substantially rigid, non-flexible, and/or non-pliable. The surface of the implant maybe a polymer, a cross-linked polymer, a ceramic, a metal, an alloy and/or a ceramic-metal composite. The implant surface may reflect a surface of the joint obtained from an image. 
     Novel devices and methods for correcting or accommodating wear patterns in joint surfaces, e.g., cartilage, meniscus and/or bone, are thus described. Advantageously, the implant has an anatomic or near-anatomic fit with the surrounding structures and tissues, thus minimizing bone cutting. In embodiments, devices provided herein also improve the anatomic functionality of the repaired joint by restoring the natural knee joint anatomy and kinematics. This, in turn, leads to an improved functional result for the repaired joint. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a block diagram of a method for assessing a joint in need of repair wherein the existing joint surface is unaltered, or substantially unaltered, prior to receiving the selected implant.  FIG. 1B  is a block diagram of a method for assessing a joint in need of repair according wherein the existing joint surface is unaltered, or substantially unaltered, prior to designing an implant suitable to achieve the repair.  FIG. 1C  is a block diagram of a method for developing an implant and using the implant in a patient. 
         FIG. 2A  is a perspective view of a joint implant suitable for implantation at the tibial plateau of the knee joint.  FIG. 2B  is a top view of the implant of  FIG. 2A .  FIG. 2C  is a cross-sectional view of the implant of  FIG. 2B  along the lines C-C shown in  FIG. 2B .  FIG. 2D  is a cross-sectional view along the lines D-D shown in  FIG. 2B .  FIG. 2E  is a cross-sectional view along the lines E-E shown in  FIG. 2B .  FIG. 2F  is a side view of the implant of  FIG. 2A .  FIG. 2G  is a cross-sectional view of the implant of  FIG. 2A  shown implanted taken along a plane parallel to the sagittal plane.  FIG. 2H  is a cross-sectional view of the implant of  FIG. 2A  shown implanted taken along a plane parallel to the coronal plane.  FIG. 2I  is a cross-sectional view of the implant of  FIG. 2A  shown implanted taken along a plane parallel to the axial plane.  FIG. 2J  shows a slightly larger implant that extends closer to the bone medially (towards the edge of the tibial plateau) and anteriorly and posteriorly.  FIG. 2K  is a side view of an alternate embodiment of the joint implant of  FIG. 2A  showing an anchor in the form of a keel.  FIG. 2L  is a bottom view of an alternate embodiment of the joint implant of  FIG. 2A  showing an anchor.  FIG. 2M  shows an anchor in the form of a cross-member.  FIGS. 2N-1, 2N-2, 2O-1 and 2O-2  are alternative embodiments of the implant showing the lower surface have a trough for receiving a cross-bar.  FIG. 2P  illustrates a variety of cross-bars.  FIGS. 2Q-R  illustrate the device implanted within a knee joint.  FIGS. 2S ( 1 - 9 ) illustrate another implant suitable for the tibial plateau further having a chamfer cut along one edge.  FIG. 2T ( 1 - 8 ) illustrate an alternate embodiment of the tibial implant wherein the surface of the joint is altered to create a flat or angled surface for the implant to mate with. 
         FIGS. 3A  and B are perspective views of a joint implant suitable for use on a condyle of the femur from the inferior and superior surface viewpoints, respectively.  FIG. 3C  is a side view of the implant of  FIG. 3A .  FIG. 3D  is a view of the inferior surface of the implant;  FIG. 3E  is a view of the superior surface of the implant and  FIG. 3F  is a cross-section of the implant.  FIG. 3G  is an axial view of a femur with the implant installed thereon.  FIG. 3H  is an anterior view of the knee joint without the patella wherein the implant is installed on the femoral condyle.  FIG. 3I  is an anterior view of the knee joint with an implant of  FIG. 3A  implanted on the femoral condyle along with an implant suitable for the tibial plateau, such as that shown in  FIG. 2 .  FIGS. 3J-K  illustrate an alternate embodiment of a joint implant for use on a condyle of a femur further having at least one chamfer cut.  FIG. 4A  illustrates an implant suitable for the femoral condyle according to the prior art.  FIGS. 4B-I  depict another implant suitable for placement on a femoral condyle.  FIG. 4B  is a slightly perspective view of the implant from the superior surface.  FIG. 4C  is a side view of the implant of  FIG. 4B .  FIG. 4D  is a top view of the inferior surface of the implant;  FIGS. 4E  and F are perspective side views of the implant.  FIG. 4G  is an axial view of a femur with the implant installed thereon.  FIG. 4H  is an anterior view of the knee joint without the patella wherein the implant is installed on the femoral condyle.  FIG. 4I  is an anterior view of the knee joint with an implant of  FIG. 4B  implanted on the femoral condyle along with an implant suitable for the tibial plateau, such as that shown in  FIG. 2 . 
         FIGS. 5A-S  are depictions of another implant suitable for placement on the femoral condyle.  FIG. 5A  is a top view of the inferior surface of the implant showing a chamfer cut.  FIG. 5B  is a slightly perspective view of the superior surface of the implant.  FIG. 5C  is a perspective side view of the implant from a first direction;  FIG. 5D  is a slightly perspective side view of the implant from a second direction.  FIGS. 5E-F  are side views of the implant showing the bearing loads;  FIGS. 5G  and H illustrate an alternative embodiment wherein the implant has lateral rails;  FIG. 5I  illustrates another embodiment wherein the implant has an anchoring keel.  FIG. 5J  is an axial view of a femur with the implant installed on the femoral condyles.  FIG. 5K  is an anterior view of the knee joint without the patella wherein the implant is installed on the femoral condyle.  FIG. 5L  is an anterior view of the knee joint with an implant of  FIG. 5A  implanted on the femoral condyles along with an implant suitable for the tibial plateau, such as that shown in  FIG. 2 .  FIGS. 5M-N  depicts a device implanted within the knee joint.  FIG. 5O  depicts an alternate embodiment of the device which accommodates an partial removal of the condyle.  FIGS. 5P-S  illustrate alternative embodiments of the implant having one or more chamfer cuts. 
         FIGS. 6A-G  illustrate a device as shown in  FIG. 5  along with a graphical representation of the cross-sectional data points comprising the surface map. 
         FIGS. 7A-C  illustrate an alternate design of a device, suitable for a portion of the femoral condyle, having a two piece configuration. 
         FIGS. 8A-J  depict a whole patella ( FIG. 8A ) and a patella that has been cut in order to install an implant ( FIG. 8B ). A top and side view of a suitable patella implant is shown ( FIGS. 8C-D ), and an illustration of the implant superimposed on a whole patella is shown to illustrate the location of the implant dome relative to the patellar ridge.  FIGS. 8E-F  illustrate the implant superimposed over a patella.  FIGS. 8G-J  illustrate an alternate design for the patella implant based on a blank ( FIG. 8G ). 
         FIGS. 9A-C  depict representative side views of a knee joint with any of the devices taught installed therein.  FIG. 9A  depicts the knee with a condyle implant and a patella implant.  FIG. 9B  depicts an alternate view of the knee with a condyle implant and a patella implant wherein the condyle implant covers a greater portion of the surface of the condyle in the posterior direction.  FIG. 9C  illustrates a knee joint wherein the implant is provided on the condyle, the patella and the tibial plateau. 
         FIGS. 10A-D  depict a frontal view of the knee joint with any of the devices taught installed therein.  FIG. 10A  depicts the knee with a tibial implant.  FIG. 10B  depicts the knee with a condyle implant.  FIG. 10C  depicts a knee with a tibial implant and a condyle implant.  FIG. 10C  depicts a knee with a bicompartmental condyle implant and a tibial implant. 
         FIG. 11  illustrates in cross-section an embodiment for the hip featuring a wear pattern correcting resurfacing implant for the femoral head. 
         FIG. 12  illustrates a glenoid component embodiment featuring an inferior wear pattern correcting surface  1228 . 
         FIG. 13  illustrates a glenoid component embodiment featuring an superior wear pattern correcting surface  1328 . 
         FIGS. 14-16  illustrate, in simplified coronal view, a tibia with medial, lateral and central lateral tibial plateau wear patterns, and a lateral tibial plateau implant featuring a wear pattern correcting surface for each respective type of wear pattern. 
         FIGS. 17-19  illustrate, in simplified sagittal view, a tibia with medial, lateral and central lateral tibial plateau wear patterns, and a lateral tibial plateau implant featuring a wear pattern correcting surface for each respective type of wear pattern. 
     
    
    
     DETAILED DESCRIPTION 
     The devices and methods described herein may replace all or a portion (e.g., diseased area and/or area slightly larger than the diseased area) of the articular surface, and achieve an anatomic or near anatomic fit with the surrounding structures and tissues. Where the devices and/or methods include an element associated with the underlying articular bone, the bone-associated element can achieve a near anatomic alignment with the bone. The articular surface may include the superior bone surface of bone ends. For example, the articular surfaces of the knee would include the femoral condyles and the tibial plateau. Healthy articular surfaces would generally be covered by cartilage, but in diseased or worn joints, the articular surface may include areas of exposed bone. 
     Some embodiments provide methods and devices for repairing joints (including bone end interfaces of the knee, hip, ankle, foot, shoulder, elbow, wrist, hand and spine), particularly for repairing articular surfaces and for facilitating integration of an articular surface repair implant into a subject. The repair may be, without limitation, a cartilage repair/resurfacing implant, a partial joint implant and/or a total joint implant on a single joint surface or multiple joint surfaces. Among other things, the techniques described herein allow for the customization of the implant to suit a particular subject, particularly in terms of correcting or accommodating a wear pattern on the articular size, cartilage thickness and/or curvature. In selected embodiments, the interior surface of the implant is a mirror image of the articular surface, i.e., it is an exact or near anatomic fit, further enhancing the success of repair is enhanced. The implant is designed to incorporate a wear pattern analysis based, on, e.g., electronic images of the articular surface. Some embodiments provide, e.g., minimally invasive methods for partial joint replacement, requiring only minimal or, in some instances, no loss in bone stock. Additionally, unlike with current techniques, the methods described herein will help to restore the integrity of the articular surface by achieving an exact or near anatomic match between the implant and the surrounding or adjacent cartilage and/or subchondral bone. 
     Methods for Measuring a Wear Pattern 
     In one embodiment, a wear pattern is determined pre-operatively or intraoperatively. Wear patterns may be assessed by, e.g.: arthroscopy; arthrotomy; imaging tests such as x-ray imaging; fluoroscopy; digital tomosynthesis; cone beam, conventional and spiral CT; bone scan; SPECT scan; PET; MRI; thermal imaging; optical imaging; and any other current and future technique for detecting articular wear; optical coherence tomography; gait analysis; and techniques merging information from one or more of these tests. 
     Many modifications and derivatives of these imaging tests can be used. For example, with MRI, images can be visually interpreted for assessing cartilage loss or bone deformity. Alternatively, computer methods including maps of cartilage thickness can be utilized for this purpose. Alternatively, a scan reflecting biomechanical composition of the articular cartilage can be performed. These include, but are not limited to, dGEMRIC, T1Rho, and T2 scans. 
     Different scanning methods within the same modalities and/or different modalities can be combined in order to determine one or more wear patterns. 
     Wear patterns may include individual or continuous areas of surface wear, disease or degradation. In some instances the wear pattern may be likened to a map of the articular surface wherein wear pattern indicia are highlighted, marked or otherwise denoted, to indicate the wear pattern. Wear pattern indicia may include the: presence, absence, location, distribution, depth, area, or dimensions of cartilage loss; presence, absence, location, distribution, depth, area, or dimensions of subchondral cysts; presence, absence, location, distribution, depth, area, or dimensions of subchondral sclerosis; presence (e.g., thickening or thinning), absence, location, distribution, volume, area, depth or dimensions of a subchondral bone plate abnormality; presence, absence, location, distribution, or dimensions of a subchondral bone deformity; presence, absence, or severity of a varus or valgus deformity; presence, absence or severity of another articular axis deformity, e.g., recurvatum, antecurvatum, or presence, absence, location, distribution, volume, depth or dimensions of bone marrow edema. 
     Parameters for Determining a Wear Pattern 
     A wear pattern can be detected, for example, by determining: presence or absence of cartilage loss; location of cartilage loss; distribution of cartilage loss; depth of cartilage loss; area of cartilage loss; width or dimensions of cartilage loss; presence or absence of subchondral cysts; location of subchondral cysts; distribution of subchondral cysts; volume of subchondral cysts; area of subchondral cysts; presence or absence of subchondral sclerosis; location of subchondral sclerosis; distribution of subchondral sclerosis; volume of subchondral sclerosis; area of subchondral sclerosis; depth or width or dimensions of subchondral sclerosis; presence or absence of abnormality of subchondral bone plate (e.g., thickening or thinning); location of abnormality of subchondral bone plate; distribution of abnormality of subchondral bone plate; volume of abnormality of subchondral bone plate; area of abnormality of subchondral bone plate; depth of abnormality of subchondral bone plate; width or dimensions of abnormality of subchondral bone plate; presence or absence of deformity of subchondral bone; location of deformity of subchondral bone; distribution of deformity of subchondral bone; area of deformity of subchondral bone; dimensions of deformity of subchondral bone; presence of absence of varus or valgus deformity; severity of varus or valgus deformity; presence or absence of other articular axis deformity, e.g., recurvatum, antecurvatum, severity of other articular axis deformity, e.g., recurvatum, antecurvatum, presence or absence of bone marrow edema; location of bone marrow edema; distribution of bone marrow edema; volume of bone marrow edema; area of bone marrow edema; depth of bone marrow edema; or dimensions of bone marrow edema. 
     One or more of these parameters can be measured preoperatively or intraoperatively. Combinations of parameters can be measured. Linear or non-linear weightings can be applied. Mathematical and statistical modeling can be used to derive a wear pattern using one or more of these parameters or combinations of parameters. 
     Other parameters can be measured such as presence and severity of ligament tears, muscle strength, body mass index, anthropometric parameters and the like. 
     Other parameters can include estimated or measured location of ligaments, e.g., medial or lateral collateral ligaments, ACL and PCL, ligamentum capitis femoris, transverse ligament, rotator cuff, spinous ligaments and the like. 
     These data can be used to improve the localization of a wear pattern. They can also be used to derive risk models of future implant wear. 
     The resultant information can be used to change or adapt and implant design or to derive an entirely new implant design adapted to a patient&#39;s wear pattern. 
     Influence on Implant Design or Selection 
     In one embodiment, a wear pattern can be determined and an implant can be designed or selected that is adapted or optimized for a patient&#39;s wear pattern. Such adaptations or optimizations can include in the area of the wear pattern or areas adjacent to a wear pattern: decrease in material thickness; increase in material thickness; change in material composition; change in cross-linking properties, e.g., via local exposure to Gamma radiation or other cross-linking reagents; change in implant shape, e.g., change in convexity or concavity of one or more surface in one or more dimensions; enhanced matching of shape between two mating articular surfaces (enhanced constraint); decreased matching of shape between two mating articular surfaces (decreased constraint). The implant may be strengthened in, without limitation, in the area of the wear pattern or areas adjacent to the wear pattern. The implant may be adapted in shape to more evenly distribute load, for example, to areas of less wear. 
     Changes in material composition can include the use of different materials, e.g., different metals or plastics or ceramics or select use of one or more of these materials in an area of wear pattern or adjacent to an area of wear pattern. Alternatively, select change in material properties of the same material can be used. For example, when a polymer material is used, select cross-linking of polymers can be performed in an area of or adjacent to a wear pattern. Such select cross-linking can, for example, be achieved, with a focused radiation beam, that is focused on the area of wear pattern, or adjacent to wear pattern. 
     Gradients in material composition and properties extending from an area of wear pattern to areas outside the wear pattern are possible. 
     Advantages of the devices and methods disclosed herein include (i) customization of joint repair, thereby enhancing the efficacy and comfort level for the patient following the repair procedure; (ii) in some embodiments, eliminating the need for a surgeon to measure the defect to be repaired intraoperatively; (iii) eliminating the need for a surgeon to shape the material during the implantation procedure; (iv) providing methods of evaluating curvature or shape of the repair material based on bone or tissue images or based on intraoperative probing techniques; (v) providing methods of repairing joints with only minimal or, in some instances, no loss in bone stock; (vi) improving postoperative joint congruity; (vii) improving the postoperative patient recovery in some embodiments, (viii) improving postoperative function, such as range of motion and joint kinematics and (ix) improving loading conditions on the implant and thus reducing risk of implant failure. 
     I. Assessment of Joints and Alignment 
     The methods and compositions described herein can be used to treat defects resulting from disease of the cartilage (e.g., osteoarthritis), bone damage, cartilage damage, trauma, and/or degeneration due to overuse or age. The size, volume and shape of the area of interest may include only the region of cartilage that has the defect, but preferably includes contiguous parts of the cartilage surrounding the cartilage defect. 
     Size, curvature and/or thickness measurements can be obtained using any suitable technique. For example, one-dimensional, two-dimensional, and/or three-dimensional measurements can be obtained using suitable mechanical means, laser devices, electromagnetic or optical tracking systems, molds, materials applied to the articular surface that harden and “memorize the surface contour,” and/or one or more imaging techniques known in the art. Measurements can be obtained non-invasively and/or intraoperatively (e.g., using a probe or other surgical device). As will be appreciated, the thickness of the repair device can vary at any given point depending upon patient&#39;s anatomy and/or the depth of the damage to the cartilage and/or bone to be corrected at any particular location on an articular surface. 
       FIG. 1A  is a flow chart showing steps taken by a practitioner in assessing a joint. First, a practitioner obtains a measurement of a target joint  10 . The step of obtaining a measurement can be accomplished by taking an image of the joint. This step can be repeated, as necessary,  11  to obtain a plurality of images in order to further refine the joint assessment process. Once the practitioner has obtained the necessary measurements, the information is used to generate a model representation of the target joint being assessed  30 . This model representation can be in the form of a topographical map or image. The model representation of the joint can be in one, two, or three dimensions, and can include a physical model. More than one model can be created  31 , if desired. Either or both the original or a subsequently created model can be used. After the model representation of the joint is generated  30 , the practitioner can optionally generate a projected model representation of the target joint in a corrected condition  40 , e.g., from the existing cartilage on the joint surface, by providing a mirror of the opposing joint surface, or a combination thereof. Again, this step can be repeated  41 , as necessary or desired. Using the difference between the topographical condition of the joint and the projected image of the joint, the practitioner can then select a joint implant  50  that is suitable to achieve the corrected joint anatomy. The selection process  50  can be repeated  51  as often as desired to achieve the desired result. Additionally, it is contemplated that a practitioner can obtain a measurement of a target joint  10  by obtaining, for example, an x-ray, and then select a suitable joint replacement implant  50 . 
     As will be appreciated, the practitioner can proceed directly from the step of generating a model representation of the target joint  30  to the step of selecting a suitable joint replacement implant  50  as shown by the arrow  32 . Additionally, following selection of suitable joint replacement implant  50 , the steps of obtaining measurement of target joint  10 , generating model representation of target joint  30  and generating projected model  40 , can be repeated in series or parallel as shown by the flow  24 ,  25 ,  26 . 
       FIG. 1B  is an alternate flow chart showing steps taken by a practitioner in assessing a joint. First, a practitioner obtains a measurement of a target joint  10 . The step of obtaining a measurement can be accomplished by taking an image of the joint. This step can be repeated, as necessary,  11  to obtain a plurality of images in order to further refine the joint assessment process. Once the practitioner has obtained the necessary measurements, the information is used to generate a model representation of the target joint being assessed  30 . This model representation can be in the form of a topographical map or image. The model representation of the joint can be in one, two, or three dimensions. The process can be repeated  31  as necessary or desired, and can include a physical model. After the model representation of the joint is assessed  30 , the practitioner can optionally generate a projected model representation of the target joint in a corrected condition  40 . This step can be repeated  41  as necessary or desired. Using the difference between the topographical condition of the joint and the projected image of the joint, the practitioner can then design a joint implant  52  that is suitable to achieve the corrected joint anatomy, repeating the design process  53  as often as necessary to achieve the desired implant design. The practitioner can also assess whether providing additional features, such as rails, keels, lips, pegs, cruciate stems, or anchors, cross-bars, etc., will enhance the implants&#39; performance in the target joint. 
     As will be appreciated, the practitioner can proceed directly from the step of generating a model representation of the target joint  30  to the step of designing a suitable joint replacement implant  52  as shown by the arrow  38 . Similar to the flow shown above, following the design of a suitable joint replacement implant  52 , the steps of obtaining measurement of target joint  10 , generating model representation of target joint  30  and generating projected model  40 , can be repeated in series or parallel as shown by the flow  42 ,  43 ,  44 . 
       FIG. 1C  is a flow chart illustrating the process of selecting an implant for a patient. First, using the techniques described above or those suitable and known in the art, the size of area of diseased cartilage or cartilage loss is measured  100 . This step can be repeated multiple times  101 , as desired. Once the size of the cartilage defect is measured, the thickness of adjacent cartilage can optionally be measured  110 . This process can also be repeated as desired  111 . Either after measuring the cartilage loss or measuring the thickness of adjacent cartilage, the curvature of the articular surface is then measured  120 . Alternatively, the subchondral bone can be measured. Measurements may also be taken of the surface of the joint being repaired, or of the mating surface in order to facilitate development of the best design for the implant surface. 
     Once the surfaces have been measured, the user either selects the best fitting implant contained in a library of implants  130 , or generates a patient-specific implant  132 . These steps can be repeated as desired or necessary,  131 ,  133 , to achieve the best-fitting implant for a patient. As will be appreciated, the process of selecting or designing an implant can be tested against the information contained in the MRI or x-ray of the patient to ensure that the surfaces of the device achieve a good fit relative to the patient&#39;s joint surface. Testing can be accomplished by, for example, superimposing the implant image over the image for the patient&#39;s joint. Once it has been determined that a suitable implant has been selected or designed, the implant site can be prepared  140 , for example by removing cartilage or bone from the joint surface, or the implant can be placed into the joint  150 . 
     The joint implant selected or designed achieves anatomic or near-anatomic fit with the existing surface of the joint while presenting a mating surface for the opposing joint surface that replicates the natural joint anatomy. In this instance, both the existing surface of the joint can be assessed as well as the desired resulting surface of the joint. This technique is particularly useful for implants that are not anchored into the bone. 
     As will be appreciated, a physician, or other person, can obtain a measurement of a target joint  10  and then either design  52  or select  50  a suitable joint replacement implant. 
     II. Repair Materials 
     A wide variety of materials find use in the practice, including, but not limited to, plastics, metals, crystal free metals, ceramics, biological materials (e.g., collagen or other extracellular matrix materials), hydroxyapatite, cells (e.g., stem cells, chondrocyte cells or the like), or combinations thereof. Based on the information (e.g., measurements) obtained regarding the defect and the articular surface and/or the subchondral bone, a repair material can be formed or selected. Further, using one or more of these techniques described herein, a cartilage replacement or regenerating material having a curvature that will fit into a particular cartilage defect, will follow the contour and shape of the articular surface, and will match the thickness of the surrounding cartilage. The repair material can include any combination of materials, and typically includes at least one non-pliable material, for example materials that are not easily bent or changed. 
     A. Metal and Polymeric Repair Materials 
     Currently, joint repair systems often employ metal and/or polymeric materials including, for example, prostheses which are anchored into the underlying bone (e.g., a femur in the case of a knee prosthesis). See, e.g., U.S. Pat. Nos. 6,203,576 and 6,322,588, and references cited therein. A wide-variety of metals are useful in the practice, and can be selected based on any criteria. For example, material selection can be based on resiliency to impart a desired degree of rigidity. Non-limiting examples of suitable metals include silver, gold, platinum, palladium, iridium, copper, tin, lead, antimony, bismuth, zinc, titanium, cobalt, stainless steel, nickel, iron alloys, cobalt alloys, such as Elgiloy®, a cobalt-chromium-nickel alloy, and MP35N, a nickel-cobalt-chromium-molybdenum alloy, and Nitinol™, a nickel-titanium alloy, aluminum, manganese, iron, tantalum, crystal free metals, such as Liquidmetal® alloys (available from Liquid Metal Technologies, www.liquidmetal.com), other metals that can slowly form polyvalent metal ions, for example to inhibit calcification of implanted substrates in contact with a patient&#39;s bodily fluids or tissues, and combinations thereof. 
     Suitable synthetic polymers include polyamides (e.g., nylon), polyesters, polystyrenes, polyacrylates, vinyl polymers (e.g., polyethylene, polytetrafluoroethylene, polypropylene and polyvinyl chloride), polycarbonates, polyurethanes, poly dimethyl siloxanes, cellulose acetates, polymethyl methacrylates, polyether ether ketones, ethylene vinyl acetates, polysulfones, nitrocelluloses, similar copolymers and mixtures thereof. Bioresorbable synthetic polymers can also be used, such as dextran, hydroxyethyl starch, derivatives of gelatin, polyvinylpyrrolidone, polyvinyl alcohol, poly[N-(2-hydroxypropyl-) methacrylamide], poly(hydroxy acids), poly(epsilon-caprolactone), polylactic acid, polyglycolic acid, poly(dimethyl glycolic acid), poly(hydroxy butyrate), and similar copolymers can also be used. 
     Other appropriate materials include polyetheretherketone (PEEK™), e.g., PEEK 450G, which is an unfilled PEEK approved for medical implantation available from Victrex (Lancashire, Great Britain, www.matweb.com), Boedeker www.boedeker.com) or Gharda (Panoli, India, www.ghardapolymers.com). The selected material may also be filled. For example, other grades of PEEK are also available, such as 30% glass-filled or 30% carbon filled, provided such materials are cleared for use in implantable devices by the FDA, or other regulatory bodies. Glass filled PEEK reduces the expansion rate and increases the flexural modulus of PEEK relative to that portion which is unfilled. The resulting product is known to be ideal for improved strength, stiffness, or stability. Carbon filled PEEK is known to enhance the compressive strength and stiffness of PEEK and lower its expansion rate. Carbon filled PEEK offers wear resistance and load carrying capability. 
     Other suitable biocompatible thermoplastic or thermoplastic polycondensate materials that resist fatigue, have good memory, are flexible, and/or deflectable have very low moisture absorption, and good wear and/or abrasion resistance, can be used. The implant can also be comprised of other polyketones, e.g., polyetherketoneketone (PEKK), polyetherketone (PEK), polyetherketoneetherketoneketone (PEKEKK), polyetheretherketoneketone (PEEKK), and polyaryletheretherketones. Other suitable polymers include those described in WO 02/02158 A1, WO 02/00275 A1, and WO 02/00270 A1. 
     Polymers can be prepared by a variety of approaches, including conventional polymer processing methods. Exemplary approaches include injection molding, which is suitable for the production of polymer components with significant structural features; and rapid prototyping, such as reaction injection molding and stereo-lithography. The substrate can be textured or made porous by either physical abrasion or chemical alteration to facilitate incorporation of the metal coating. Other suitable processes include extrusion, injection, compression molding and/or machining techniques. Typically, the polymer is chosen for its physical and mechanical properties and is suitable for carrying and spreading the physical load between the joint surfaces. 
     More than one metal and/or polymer can be used in combination with each other. For example, one or more metal-containing substrates can be coated with polymers in one or more regions or, alternatively, one or more polymer-containing substrate can be coated in one or more regions with one or more metals. 
     The system or prosthesis can be porous or porous-coated. The porous surface components can be made of various materials including metals, ceramics, and polymers. These surface components can, in turn, be secured by various means to a multitude of structural cores formed of various metals. Suitable porous coatings include metal, ceramic, polymeric (e.g., biologically neutral elastomers such as silicone rubber, polyethylene terephthalate and/or combinations thereof or combinations thereof. See, e.g., U.S. Pat. Nos. 3,605,123, 3,808,606, 3,843,975, 3,314,420, 3,987,499 and German Offenlegungsschrift 2,306,552. There can be more than one coating layer, and the layers can have the same or different porosities. See, e.g., U.S. Pat. No. 3,938,198. 
     The coating can be applied by surrounding a core with powdered polymer and heating until cured to form a coating with an internal network of interconnected pores. The tortuosity of the pores (e.g., a measure of length to diameter of the paths through the pores) can be important in evaluating the probable success of such a coating in use on a prosthetic device. See also U.S. Pat. No. 4,213,816. The porous coating can be applied in the form of a powder and the article as a whole subjected to an elevated temperature that bonds the powder to the substrate. Selection of suitable polymers and/or powder coatings can be determined in view of the teachings and references cited herein, for example, based on the melt index of each. 
     Depending on a wear pattern analysis, it may be advantageous to utilize differing materials or material composition (e.g., varying degrees of polymeric cross linking, or of metal/alloy hardness) in the implant body to address and correct the wear pattern. Variations in material composition throughout the implant body can include the use of different materials, e.g., different metals, plastics or ceramics, or the selection of one or more of these materials in, or adjacent to, the region of the implant corresponding to a wear pattern. As noted above, select changes in material properties of the same material can be used; or, when a polymeric material is employed, selective cross-linking can be performed in an area of or adjacent to a wear pattern to selectively vary the physical properties of the polymer. Selective cross-linking can be achieved, for example with a radiation beam focused on, or adjacent to, the area of the device corresponding to the wear pattern, or by use of selective chemical cross linking. 
     A wear pattern analysis may include reviewing or analyzing a bone surface to determine the presence of wear pattern indicia. The review or analysis may be determined preoperatively (e.g., via imaging analysis) or intraoperatively, e.g., via arthroscopy, arthrotomic examination, or gait analysis. Linear or non-linear weightings can be applied; and mathematical and statistical modeling can be used to derive a wear pattern from the wear pattern indicia. Other parameters can be considered in determining a wear pattern, including the presence and severity of ligament tears, muscle strength, body mass index, anthropometric parameters, and the estimated or measured location of ligaments, e.g., medial or lateral collateral ligaments, ACL and PCL, ligamentum capitis femoris, transverse ligaments, rotator cuff, and spinous ligaments. 
     Further considerations in designing the implant body to address and correct the wear pattern include decreasing or increasing material thickness in response to the wear pattern (e.g., part of designing a characteristic topography); change in implant shape, e.g., change in convexity or concavity of one or more surfaces in one or more dimensions; enhanced matching of shape between two mating articular surfaces (enhanced constraint); or decreased matching of shape between two mating articular surfaces (decreased constraint). A characteristic topography may include the relief features of the superior surface, but also variations in thickness of the device from region to region (elevation, in topographic terms.) In an embodiment, an implant can be designed or selected that is adapted or optimized for a patient&#39;s wear pattern or areas adjacent to a wear pattern, such adaptations or optimizations resulting in an implant having a characteristic topography. 
     B. Biological Repair Materials 
     Repair materials can also include one or more biological material either alone or in combination with non-biological materials. For example, any base material can be designed or shaped and suitable cartilage replacement or regenerating material(s) such as fetal cartilage cells can be applied to be the base. The cells can be then be grown in conjunction with the base until the thickness (and/or curvature) of the cartilage surrounding the cartilage defect has been reached. Conditions for growing cells (e.g., chondrocytes) on various substrates in culture, ex vivo and in vivo are described, for example, in U.S. Pat. Nos. 5,478,739, 5,842,477, 6,283,980, and 6,365,405. Non-limiting examples of suitable substrates include plastic, tissue scaffold, a bone replacement material (e.g., a hydroxyapatite, a bioresorbable material), or any other material suitable for growing a cartilage replacement or regenerating material on it. 
     Biological polymers can be naturally occurring or produced in vitro, e.g., via fermentation. Suitable biological polymers include collagen, elastin, silk, keratin, gelatin, polyamino acids, cat gut sutures, polysaccharides (e.g., cellulose and starch) and mixtures thereof. Biological polymers can be bioresorbable. Biological materials can be autografts (from the same subject); allografts (from another individual of the same species) and/or xenografts (from another species). See also WO 02/22014 and WO 97/27885. In certain embodiments autologous materials are preferred, as they can carry a reduced risk of immunological complications to the host, including re-absorption of the materials, inflammation and/or scarring of the tissues surrounding the implant site. 
     Any biological repair material can be sterilized to inactivate biological contaminants such as bacteria, viruses, yeasts, molds, mycoplasmas and parasites. Sterilization can be performed using any suitable technique such as radiation, e.g., gamma radiation. 
     Any of the biological materials described herein can be harvested with use of a robotic device. The robotic device can use information from an electronic image for tissue harvesting. 
     III. Device Design 
     A. Cartilage Models 
     Using information on thickness and curvature of the cartilage, a physical model of the surfaces of the articular cartilage and of the underlying bone can be created. This physical model can be representative of a limited area within the joint or it can encompass the entire joint. This model can also take into consideration the presence or absence of a meniscus as well as the presence or absence of some or all of the cartilage. For example, in the knee joint, the physical model can encompass only the medial or lateral femoral condyle, both femoral condyles and the notch region, the medial tibial plateau, the lateral tibial plateau, the entire tibial plateau, the medial patella, the lateral patella, the entire patella or the entire joint. The location of a diseased area of cartilage can be determined, for example using a 3D coordinate system or a 3D Euclidian distance as described in WO 02/22014. 
     In this way, the size of the defect to be repaired can be determined. This process takes into account that, for example, roughly 80% of patients have a healthy lateral component. As will be apparent, some, but not all, defects will include less than the entire cartilage. Thus, in one embodiment, the thickness of the normal or only mildly diseased cartilage surrounding one or more cartilage defects is measured. This thickness measurement can be obtained at a single point or, preferably, at multiple points, for example 2 point, 4-6 points, 7-10 points, more than 10 points or over the length of the entire remaining cartilage. Furthermore, once the size of the defect is determined, an appropriate therapy (e.g., articular repair system) can be selected such that as much as possible of the healthy, surrounding tissue is preserved. 
     In other embodiments, the curvature of the articular surface can be measured to design and/or shape the repair material. Further, both the thickness of the remaining cartilage and the curvature of the articular surface can be measured to design and/or shape the repair material. Alternatively, the curvature of the subchondral bone can be measured and the resultant measurement(s) can be used to either select or shape a cartilage replacement material. For example, the contour of the subchondral bone can be used to re-create a virtual cartilage surface: the margins of an area of diseased cartilage can be identified. The subchondral bone shape in the diseased areas can be measured. A virtual contour can then be created by copying the subchondral bone surface into the cartilage surface, whereby the copy of the subchondral bone surface connects the margins of the area of diseased cartilage. In shaping the device, the contours can be configured to mate with existing cartilage or to account for the removal of some or all of the cartilage. 
       FIG. 2A  shows a slightly perspective top view of a joint implant  200  suitable for implantation at the tibial plateau of the knee joint. As shown in  FIG. 2A , the implant can be generated using, for example, a dual surface assessment, as described above with respect to  FIGS. 1A  and B. 
     The implant  200  has an upper surface  202 , a lower surface  204  and a peripheral edge  206 . The upper surface  202  is formed so that it forms a mating surface for receiving the opposing joint surface; in this instance partially concave to receive the femur. The concave surface can be variably concave such that it presents a surface to the opposing joint surface, e.g., a negative surface of the mating surface of the femur it communicates with. As will be appreciated, the negative impression need not be a perfect one. 
     The upper surface  202  of the implant  200  can be shaped by a variety of means. For example, the upper surface  202  can be shaped by projecting the surface from the existing cartilage and/or bone surfaces on the tibial plateau, or it can be shaped to mirror the femoral condyle in order to optimize the complimentary surface of the implant when it engages the femoral condyle. Alternatively, the superior surface  202  (e.g., the outer surface of the implant, i.e., that which will interface with the opposing joint surface, or an implant affixed to the opposing joint surface) can be configured to mate with an inferior surface (e.g., the surface of the implant body that faces the articular surface to which the implant is to be affixed) of an implant configured for the opposing femoral condyle. 
     The lower surface  204  has a convex surface that matches, or nearly matches, the tibial plateau of the joint such that it creates an anatomic or near anatomic fit with the tibial plateau. Depending on the shape of the tibial plateau, the lower surface can be partially convex as well. Thus, the lower surface  204  presents a surface to the tibial plateau that fits within the existing surface. It can be formed to match the existing surface or to match the surface after articular resurfacing. 
     As will be appreciated, the convex surface of the lower surface  204  need not be perfectly convex. Rather, the lower surface  204  is more likely consist of convex and concave portions that fit within the existing surface of the tibial plateau or the re-surfaced plateau. Thus, the surface is essentially variably convex and concave. 
       FIG. 2B  shows a top view of the joint implant of  FIG. 2A . As shown in  FIG. 2B  the exterior shape  208  of the implant can be elongated. The elongated form can take a variety of shapes including elliptical, quasi-elliptical, race-track, etc. However, as will be appreciated the exterior dimension is typically irregular thus not forming a true geometric shape, e.g., elliptical. As will be appreciated, the actual exterior shape of an implant can vary depending on the nature of the joint defect to be corrected. Thus the ratio of the length L to the width W can vary from, for example, between 0.25 and 2.0, and more particularly from 0.5 to 1.5. As further shown in  FIG. 2B , the length across an axis of the implant  200  varies when taken at points along the width of the implant. For example, as shown in  FIG. 2B , L 1 ≠L 2 ≠L 3 . 
     Turning now to  FIGS. 2C-E , cross-sections of the implant shown in  FIG. 2B  are depicted along the lines of C-C, D-D, and E-E. The implant has a thickness t 1 , t 2  and t 3  respectively. As illustrated by the cross-sections, the thickness of the implant varies along both its length L and width W. The actual thickness at a particular location of the implant  200  is a function of the thickness of the cartilage and/or bone to be replaced and the joint mating surface to be replicated. Further, the profile of the implant  200  at any location along its length L or width W is a function of the cartilage and/or bone to be replaced. 
       FIG. 2F  is a lateral view of the implant  200  of  FIG. 2A . In this instance, the height of the implant  200  at a first end h 1  is different than the height of the implant at a second end h 2 . Further the upper edge  208  can have an overall slope in a downward direction. However, as illustrated the actual slope of the upper edge  208  varies along its length and can, in some instances, be a positive slope. Further the lower edge  210  can have an overall slope in a downward direction. As illustrated the actual slope of the lower edge  210  varies along its length and can, in some instances, be a positive slope. As will be appreciated, depending on the anatomy of an individual patient, an implant can be created wherein h 1  and h 2  are equivalent or substantially equivalent without departing from the scope. 
       FIG. 2G  is a cross-section taken along a sagittal plane in a body showing the implant  200  implanted within a knee joint  1020  such that the lower surface  204  of the implant  200  lies on the tibial plateau  1022  and the femur  1024  rests on the upper surface  202  of the implant  200 .  FIG. 2H  is a cross-section taken along a coronal plane in a body showing the implant  200  implanted within a knee joint  1020 . As is apparent from this view, the implant  200  is positioned so that it fits within a superior articular surface  224 . As will be appreciated, the articular surface may be the medial or lateral facet, as needed. 
       FIG. 2I  is a view along an axial plane of the body showing the implant  200  implanted within a knee joint  1020  showing the view taken from an aerial, or upper, view.  FIG. 2J  is a view of an alternate embodiment where the implant is a bit larger such that it extends closer to the bone medially, i.e., towards the edge  1023  of the tibial plateau, as well as extending anteriorly and posteriorly. 
       FIG. 2K  is a cross-section of an implant  200  according to an alternate embodiment. In this embodiment, the lower surface  204  further includes a joint anchor  212 . As illustrated in this embodiment, the joint anchor  212  forms a protrusion, keel or vertical member that extends from the lower surface  204  of the implant  200  and projects into, for example, the bone of the joint. As will be appreciated, the keel can be perpendicular or lie within a plane of the body. 
     Additionally, as shown in  FIG. 2L  the joint anchor  212  can have a cross-member  214  so that from a bottom perspective, the joint anchor  212  has the appearance of a cross or an “x.” As will be appreciated, the joint anchor  212  may take on a variety of other forms while still accomplishing the same objective of providing increased stability of the implant  200  in the joint. These forms include, but are not limited to, pins, bulbs, balls, teeth, etc. Additionally, one or more joint anchors  212  can be provided as desired.  FIGS. 2M  and N illustrate cross-sections of alternate embodiments of a dual component implant from a side view and a front view. 
     In an alternate embodiment shown in  FIG. 2M  it may be desirable to provide a one or more cross-members  220  on the lower surface  204  in order to provide a bit of translation movement of the implant relative to the surface of the femur, or femur implant. In that event, the cross-member can be formed integral to the surface of the implant or can be one or more separate pieces that fit within a groove  222  on the lower surface  204  of the implant  200 . The groove can form a single channel as shown in  FIG. 2N-1 , or can have more than one channel as shown in  FIG. 2O-1 . In either event, the cross-bar then fits within the channel as shown in  FIGS. 2N-2 and 2O-2 . The cross-bar members  220  can form a solid or hollow tube or pipe structure as shown in  FIG. 2P . Where two, or more, tubes  220  communicate to provide translation, a groove  221  can be provided along the surface of one or both cross-members to interlock the tubes into a cross-bar member further stabilizing the motion of the cross-bar relative to the implant  200 . As will be appreciated, the cross-bar member  220  can be formed integrally with the implant without departing from the scope. 
     As shown in  FIGS. 2Q-R , it is anticipated that the surface of the tibial plateau will be prepared by forming channels thereon to receive the cross-bar members. Thus facilitating the ability of the implant to seat securely within the joint while still providing movement about an axis when the knee joint is in motion. 
       FIG. 2S ( 1 - 9 ) illustrate an alternate embodiment of implant  200 . As illustrated in  FIG. 2S  the edges are beveled to relax a sharp corner.  FIG. 2S ( 1 ) illustrates an implant having a single fillet or bevel  230 . The fillet is placed on the implant anterior to the posterior portion of the tibial spine. As shown in  FIG. 2S ( 2 ) two fillets  230 ,  231  are provided and used for the posterior chamfer. In  FIG. 2S ( 3 ) a third fillet  234  is provided to create two cut surfaces for the posterior chamfer. 
     Turning now to  FIG. 2S ( 4 ) a tangent of the implant is deselected, leaving three posterior curves.  FIG. 2S ( 5 ) shows the result of tangent propagation.  FIG. 2S ( 6 ) illustrates the effect on the design when the bottom curve is selected without tangent propagation. The result of tangent propagation and selection is shown in  FIG. 2S ( 7 ). As can be seen in  FIG. 2S ( 8 - 9 ) the resulting corner has a softer edge but sacrifices less than 0.5 mm of joint space. As will be appreciated, additional cutting planes can be added without departing from the scope. 
       FIG. 2T  illustrates an alternate embodiment of an implant  200  wherein the surface of the tibial plateau  250  is altered to accommodate the implant. As illustrated in  FIG. 2T ( 1 - 2 ) the tibial plateau can be altered for only half of the joint surface  251  or for the full surface  252 . As illustrate in  FIG. 2T ( 3 - 4 ) the posterior-anterior surface can be flat  260  or graded  262 . Grading can be either positive or negative relative to the anterior surface. Grading can also be used with respect to the implants of  FIG. 2T  where the grading either lies within a plane or a body or is angled relative to a plane of the body. Additionally, attachment mechanisms can be provided to anchor the implant to the altered surface. As shown in  FIG. 2T ( 5 - 7 ) keels  264  can be provided. The keels  264  can either sit within a plane, e.g., sagittal or coronal plane, or not sit within a plane (as shown in  FIG. 2T ( 7 )).  FIG. 2T ( 8 ) illustrates an implant which covers the entire tibial plateau. The upper surface of these implants are designed to conform to the projected shape of the joint as determined under the steps described with respect to  FIG. 1 , while the lower surface is designed to be flat, or substantially flat to correspond to the modified surface of the joint. 
     Turning now to  FIGS. 3A-I , an implant suitable for providing an opposing joint surface to the implant of  FIG. 2A  is shown. This implant corrects a defect on an inferior surface of the femur  1024  (e.g., the condyle of the femur that mates with the tibial plateau) and can be used alone, i.e., on the femur  1024 , or in combination with another joint repair device. Formation of the surfaces of the devices can be achieved using the techniques described above with respect to the implant of  FIG. 2 . 
       FIG. 3A  shows a perspective view of an implant  300  having a curved mating surface  302  and convex joint abutting surface  304 . The joint abutting surface  304  need not form an anatomic or near anatomic fit with the femur in view of the anchors  306  provided to facilitate connection of the implant to the bone. In this instance, the anchors  306  are shown as pegs having notched heads. The notches facilitate the anchoring process within the bone. However, pegs without notches can be used as well as pegs with other configurations that facilitate the anchoring process or cruciate stems. Pegs and other portions of the implant can be porous-coated. The implant can be inserted without bone cement or with use of bone cement. The implant can be designed to abut the subchondral bone, i.e., it can substantially follow the contour of the subchondral bone. This has the advantage that no bone needs to be removed other than for the placement of the peg holes thereby significantly preserving bone stock. 
     The anchors  306  may take on a variety of other forms, while still accomplishing the objective of providing increased stability of the implant  300  in the joint. These forms include, but are not limited to, pins, bulbs, balls, teeth, etc. Additionally, one or more joint anchors  306  can be provided as desired. As illustrated in  FIG. 3 , three pins are used to anchor the implant  300 . However, more or fewer joint anchors, cruciate stems, or pins, can be used without departing from the scope. 
       FIG. 3B  shows a slightly perspective superior view of the bone mating surface  304  further illustrating the use of three anchors  306  to anchor the implant to the bone. Each anchor  306  has a stem  310  with a head  312  on top. As shown in  FIG. 3C , the stem  310  has parallel walls such that it forms a tube or cylinder that extends from the bone mating surface  304 . A section of the stem forms a narrowed neck  314  proximal to the head  312 . As will be appreciated, the walls need not be parallel, but rather can be sloped to be shaped like a cone. Additionally, the neck  314  need not be present, or the head  312 . As discussed above, other configurations suitable for anchoring can be used without departing from the scope. 
     Turning now to  FIG. 3D , a view of the tibial plateau mating surface  302  of the implant  300  is illustrated. As is apparent from this view, the surface is curved such that it is convex or substantially convex in order to mate with the concave surface of the plateau.  FIG. 3E  illustrates the upper surface  304  of the implant  300  further illustrating the use of three pegs  306  for anchoring the implant  300  to the bone. As illustrated, the three pegs  306  are positioned to form a triangle. However, as will be appreciated, one or more pegs can be used, and the orientation of the pegs  306  to one another can be as shown or any other suitable orientation that enables the desired anchoring.  FIG. 3F  illustrated a cross section of the implant  300  taken along the lines F-F shown in  FIG. 3E . Typically the pegs are oriented on the surface of the implant so that the peg is perpendicular to the femoral condyle, which may not result in the peg being perpendicular to the surface of the implant. 
       FIG. 3G  illustrates the axial view of the femur  1000  having a lateral condyle  1002  and a medial condyle  1004 . The intercondylar fossa is also shown  1006  along with the lateral epicondyle  1008  and medial epicondyle  1010 . Also shown is the patellar surface of the femur  1012 . The implant  300  illustrated in  FIG. 3A , is illustrated covering a portion of the lateral condyle. The pegs  306  are also shown that facilitate anchoring the implant  300  to the condyle. 
       FIG. 3H  illustrates a knee joint  1020  from an anterior perspective. The implant  300  is implanted over a condyle. As shown in  FIG. 3I , the implant  300  is positioned such that it communicates with an implant  200  designed to correct a defect in the tibial plateau, such as those shown in  FIG. 2 . 
       FIGS. 3J-K  illustrate an implant  300  for placement on a condyle. In this embodiment, at least one flat surface or chamfer cut  360  is provided to mate with a cut made on the surface of the condyle in preparing the joint. The flat surface  360  typically does not encompass the entire proximal surface  304  of the implant  300 . 
       FIG. 4A  illustrates the design of a typical total knee arthroplasty (“TKA”) primary knee  499 . Posterior cuts  498 , anterior cuts  497  and distal cuts  496  are provided as well as chamfer cuts  495 . 
       FIGS. 4B and 4C  illustrate another implant  400 . As shown in  FIG. 4B , the implant  400  is configured such that it covers both the lateral and medial femoral condyle, along with the patellar surface of the femur  1012 . The implant  400  has a lateral condyle component  410  and a medial condyle component  420  and a bridge  430  that connects the lateral condyle component  410  to the medial condyle component  420  while covering at least a portion of the patellar surface of the femur  1012 . The implant  400  can optionally oppose one or more implants, such as those shown in  FIG. 2 , if desired.  FIG. 4C  is a side view of the implant of  FIG. 4B . As shown in  FIG. 4C , the superior surface  402  of the implant  400  is curved to correspond to the curvature of the femoral condyles. The curvature can be configured such that it corresponds to the actual curvature of one or both of the existing femoral condyles, or to the curvature of one or both of the femoral condyles after resurfacing of the joint. One or more pegs  430  can be provided to assist in anchoring the implant to the bone. As will be appreciated, the implant can be configured such that the superior surface contacting a first condyle is configured to male with the existing condyle while a surface contacting a second condyle has one or more flat surfaces to mate with a condyle surface that has been modified. 
       FIG. 4D  illustrates a top view of the implant  400  shown in  FIG. 4B . As should be appreciated from this view, the inferior surface  404  of the implant  400  is configured to conform to the shape of the femoral condyles, e.g., the shape healthy femoral condyles would present to the tibial surface in a non-damaged joint. 
       FIGS. 4E  and F illustrate perspective views of the implant from the inferior surface (i.e., tibial plateau mating surface). 
       FIG. 4G  illustrates the axial view of the femur  1000  having a lateral condyle  1002  and a medial condyle  1004 . The intercondylar fossa is also shown  1006  along with the lateral epicondyle  1008 . The implant  400  illustrated in  FIG. 4B  is illustrated covering both condyles and the patellar surface of the femur  1012 . The pegs  430  are also shown that facilitate anchoring the implant  400  to the condyle. 
       FIG. 4H  illustrates a knee joint  1050  from an anterior perspective. The implant  400  is implanted over both condyles. As shown in  FIG. 4I , the implant  400  is positioned such that it communicates with an implant  200  designed to correct a defect in the tibial plateau, such as those shown in  FIG. 2 . 
     As will be appreciated, the implant  400  can be manufactured from a material that has memory such that the implant can be configured to snap-fit over the condyle. Alternatively, it can be shaped such that it conforms to the surface without the need of a snap-fit. 
       FIGS. 5A and 5B  illustrate yet another implant  500  suitable for repairing a damaged condyle. As shown in  FIG. 5A , the implant  500  is configured such that it covers only one of the lateral or medial femoral condyles  510 . The implant differs from the implant of  FIG. 3  in that the implant  500  also covers at least a portion of the patellar surface of the femur  512 . 
     Similar to the implant of  FIG. 4 , the implant can optionally oppose one or more implants or opposing joint surfaces, such as those shown in  FIG. 2 , and can be combined with other implants, such as the implants of  FIG. 3 .  FIG. 5C  is a perspective side view of the implant of  FIG. 5A . As shown in  FIG. 5C , the superior surface  502  of the implant  500  is curved to correspond to the curvature of the femoral condyle that it mates with and the portion of the patellar surface of the femur that it covers. One or more pegs  530  can be provided to assist in anchoring the implant to the bone. Additionally, an angled surface  503  can be provided on an interior surface  502  of the condyle component that conforms to an optionally provided cut made on the surface of the joint surface with which the implant mates. 
       FIG. 5D  illustrates a perspective top view of the implant  500  shown in  FIG. 5A . It may be appreciated from this view that the inferior surface  504  of the implant  500  is configured to conform to the projected shape of the femoral condyles, e.g., the shape healthy femoral condyles would present to the tibial surface in a non-damaged joint. 
       FIG. 5E  is a view of the implant  500  showing a hatched three point loading support area which extends from a top portion  513  to a line (plane  17 ) and from a line (plane  18 ) to a bottom portion  515 . Also illustrated are the pegs  530  extending from the superior surface.  FIG. 5F  illustrates the superior surface of the implant  500  with the pegs  530  extending from the superior surface.  FIG. 5F  also illustrates the hatched cantilever loading support area, which extends from the line (plane  18 ) to the top portion  513  of the implant. The loading forces and directions for each support condition are based on physiological load encounters. Table 1 shows the Physiological Loadings taken from a study by Seth Greenwald. 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Physiological Loadings 1   
               
             
          
           
               
                 Set-up 
                 “1” 
                 “2” 
                 “3” 
               
               
                   
               
               
                 Flexion Angle 
                 0° 
                 60° 
                 90° 
               
               
                 (degree) 
               
               
                 Normal Force N 
                 2,900 
                 3,263 
                 3,625 
               
               
                 (lbs.) 
                 (652) 
                 (733.5) 
                 (815) 
               
               
                 Normal Force 
                 Walking 
                 Stair Descent 
                 Stair Ascent 
               
               
                 Case 
                 (4.0 × BW ¥ ) 
                 (4.5 × BW ¥ ) 
                 (5.0 × BW ¥ ) 
               
               
                   
               
               
                   ¥ Body Weight (BW) taken as a 60 year old male, with 173 cm height for an average body weight of 74 kg (163 lbs). 
               
               
                   1 “Tibial Plateau Surface Stress in TKA: A Factor Influencing Polymer Failure Series III-Posterior Stabilized Designs;” Paul D. Postak, B.Sc., Christine S. Heim, B.Sc., A. Seth Greenwald, D. Phil.; Orthopaedic Research Laboratories, The Mt. Sinai Medical Center, Cleveland, Ohio. Presented at the 62 nd  Annual AAOS Meeting, 1995. 
               
             
          
         
       
     
     Using the implant  500  described in this application, the three point loading will occur from set-up 1 (2900 N). To replicate a worst case loading scenario, a 75/25 load distribution (75% of 2900 N=2175 N) can be used. The loading will be concentrated on a 6 mm diameter circular area located directly below and normal to the pad on the bearing surface. 
     Turning to the cantilever loading shown in  FIG. 5F , the loading will occur from set-up 3, or 90°, at a 75/25 load distribution (75% of 3625 N=2719 N). As with the above example, the loading will be concentrated on a 6 mm diameter circular area located at the center of the posterior-most portion of the medial condyle normal to the flat cut surface of the posterior condyle. 
       FIGS. 5G  and H illustrate alternate embodiments of the implant  500  having a rail design that provides one or more rails  521  along medial and/or lateral sides of the implant  500 . The rail  521  can be positioned so that it extends along a portion of the medial  517  and/or lateral  519  sides before communicating with the angled surface  503 . As will be appreciated, a single side rail  521  can also be provided. 
       FIG. 5I  illustrates another embodiment of an implant  500  having a keel design. A keel  523  (or centrally formed rail) is provided on the superior surface of the implant. In this embodiment, the keel  523  is located on the surface of the implant, but not at the sides. As will be appreciated, the keel can be centered, as shown, substantially centered, or located off-center. An angled surface  503  can be provided to communicate with a modified joint surface. Alternatively, where the joint surface is worn or modified, the cut  503  may be configured to mate with the worn or modified surface. 
       FIG. 5J  illustrates the axial view of the femur  1000  having a lateral condyle  1002  and a medial condyle  1004 . The intercondylar fosse is also shown  1006  along with the lateral epicondyle  1008  and the medial epicondyle  1010 . The patellar surface of the femur  1012  is also illustrated. The implant  500 , illustrated in  FIG. 5A , is shown covering the lateral condyle and a portion of the patellar surface of the femur  1012 . The pegs  530  facilitate anchoring the implant  500  to the condyle and patellar surface. 
       FIG. 5K  illustrates a knee joint  1020  from an anterior perspective. The implant  500  is implanted over the lateral condyle.  FIG. 5L  illustrates a knee joint  1020  with the implant  500  covering the medial condyle  1004 . As illustrated in  FIGS. 5K  and L, the shape of the implant  500  corresponding to the patella surface may take on a variety of curvatures. 
     Turning now to  FIGS. 5M  and N the implant  500  is positioned such that it communicates with an implant  200  designed to correct a defect in the tibial plateau, such as those shown in  FIG. 2 . 
     In another embodiment, the implant  500  has a superior surface  502  which substantially conforms to the surface of the condyle but which has at one flat portion corresponding to an oblique cut on the bone as shown in  FIG. 5O . 
     Turning now to  FIG. 5P-Q , an implant  500  is shown from a side view with a 7° difference between the anterior and posterior cuts. 
       FIG. 5R-S  illustrate an implant  500  having a contoured surface  560  for mating with the joint surface and an anterior cut  561  and a posterior cut  562 .  FIG. 5S  shows the same implant  500  from a slightly different angle.  FIG. 5T  illustrates another implant  500  having a contoured surface  560  for mating with the joint surface and posterior cut  562 , a distal cut  563 , and a chamfer cut  564 . In this embodiment no anterior cut is provided.  FIG. 5U  illustrates the implant  500  of  FIG. 5T  from a side perspective. The cuts are typically less than the cut required for a TKA, i.e., typically less than 10 mm. The design of the cuts for this implant allow for a revision surgery to the knee, if required, at a later date. 
       FIGS. 6A-G  illustrate the implant  500  of  FIG. 5  with a graphical representation of the cross-sections  610 ,  620  from which a surface shape of the implant is derived.  FIG. 6A  illustrates a top view of the implant  500  sitting on top of the extracted surface shape  600 . This view of the implant  500  illustrates a notch  514  associated with the bridge section of the implant  512  which covers the patellar surface of the femur (or the trochlear region) to provide a mating surface that approximates the cartilage surface. As will be appreciated, the shape of an implant designed for the medial condyle would not necessarily be a mirror image of the implant designed for the lateral condyle because of differences in anatomy. Thus, for example, the notch  514  would not be present in an implant designed for the medial condyle and the patellar surface of the femur. Therefore, the implant can be designed to include all or part of the trochlear region, or to exclude it entirely. 
       FIG. 6B  illustrates a bottom view of the implant  500  layered over another derived surface shape  601 .  FIG. 6C  is a bottom view showing the implant  500  extending through the extracted surface shape  600  shown in  FIG. 6A .  FIG. 6D  is a close-up view of  FIG. 6C , showing the condylar wing of the implant covering the extracted surface  600 .  FIG. 6E  illustrates a top posterior view of the implant  500  positioned over the graphical representation of the surface shape  600 .  FIG. 6F  is an anterior view and  FIG. 6G  is a bottom-posterior view. 
       FIG. 7A-C  illustrate an implant  700  for correcting a joint similar to the implant  500  above. However, implant  700  consists of two components. The first component  710  engages a condyle of the femur, either medial or lateral depending on the design. The second component  720  engages the patellar surface of the femur. As discussed with the previous embodiments, the surfaces of the implant  700  may be configured such that the distal surface  722  (e.g., the surface that faces the tibial plateau) is shaped based on a projection of the natural shape of the femur compensating the design for valgus or varus deformities and/or flattening of the surface of the femur. Alternatively, the distal surface can be shaped based on the shape of the tibial plateau to provide a surface designed to optimally mate with the tibial plateau. The proximal surface  724  (e.g., the surface that engages the femoral condyle) can be configured such that it mirrors the surface of the femur in either its damaged condition or its modified condition. Likewise, the proximal surface can have one or more flattened sections  726  that form, e.g., chamfer cuts. Additionally the surface can include mechanisms facilitating attachment  728  to the femur, such as keels, teeth, cruciate stems, and the like. The medial facing portion of the condyle implant has a tapered surface  730  while the lateral facing portion of the patellar component also has a tapered surface such that each component presents tapered surfaces  730  to the other component. 
     By dividing the surfaces of the medial and lateral compartments into independent articulating surfaces, as shown in  FIG. 7 , the implant provides improved fit of the conformal surfaces to the subchondral bone. Additionally, the lateral-anterior portion of the femur is shielded from stress which could cause bone loss. Also, the smaller size of each component of the implant enables the implant to be placed within the joint using a smaller incision. Finally, the wear of the patellar component is improved. 
       FIGS. 8A-F  illustrate a patella  800  with an implant  810 . The implant  810  can have one or more pegs, cruciate stems, or other anchoring mechanisms, if desired. As will be appreciated, other designs can be arrived at using the teachings of this disclosure.  FIG. 8A  illustrates a perspective view of an intact patella  800 .  FIG. 8B  illustrates the patella  800  wherein one surface of the patella  800  has been cut for form a smooth surface  802  to mate with an implant.  FIG. 8C  illustrates the patella  800  with an implant  810  positioned on the smooth surface  802 . The implant  810  has a plate structure  812  that abuts the smooth surface of the patella  802  and a dome  814  positioned on the plate  812  so that the dome is positioned in situ such that it will match the location of the patellar ridge. The implant  810  can be configured such that the edge of the plate is offset 1 mm from the actual edge of the patella, as illustrated. As will be appreciated, the plate  812  and dome  814  can be formed as a single unit or formed from multiple components.  FIG. 8D  is a side view of the implant  810  positioned on the patella  800 . As shown, the dome is positioned on the implant such that it is off-center. Optimal positioning of the dome will be determined by the position of the patellar ridge. 
     Turning now to  FIGS. 8E-F , the implant  810  is shown superimposed on the unaltered patella  800  in order to illustrate that the position of the dome  814  of the implant corresponds to the location of the patellar ridge. 
       FIGS. 8G-J  illustrate an alternative design for the patellar implant.  FIG. 8G  illustrates the implant  850  in its beginning stages as a blank with a flat inferior surface  852  having pegs  854  extending therefrom for anchoring to the patella. The articular or superior surface  860  has a rounded dome  856 , and a round plate section  858  that can be machined to match the bone cut. The articular surface  860  takes on the appearance of a “hat” or sombrero, having a dome with a rim. The center of the dome  856  is also the center of the bearing surface. The rim  858  is cut to conform to the needs of the particular patient.  FIG. 8J  illustrates an implant which has been formed from the blank shown in  FIGS. 8G-I .  FIG. 81  shows a plurality of possible cut lines  862 ,  862 ′ for purposes of illustration. 
       FIGS. 9A-C  illustrate a lateral view of a knee  1020  with a combination of implants. In  FIG. 9A , an implant covering the condyle  900 , is illustrated. Suitable implants can be, for example, those shown in  FIGS. 3-8 , as will be appreciated the portion of the condyle covered anterior to posterior can include the entire weight bearing surface, a portion thereof, or a surface greater than the weight bearing surface. Thus, for example, the implant can be configured to terminate prior to the sulcus terminalis or after the sulcus terminalis (e.g., the groove on the femur that coincides with the area where load bearing on the joint surface stops). As shown in  FIGS. 9A-B , a patellar implant  900  can also be provided.  FIG. 9C  illustrates a knee having a condyle implant  900 , a patellar implant  800  and an implant for the tibial plateau  200 . 
       FIGS. 10A-D  provide an alternate view of the coronal plane of a knee joint with one or more implants described above implanted therein.  FIG. 10A  illustrates a knee having a tibial implant  200  placed therein.  FIG. 10B  illustrates a knee with a condyle implant  300  placed therein. As described above, a plurality of the implants taught herein can be provided within a joint in order to restore joint movement.  FIG. 10C  illustrates a knee joint having two implants therein. First, a tibial implant  200  is provided on the tibial plateau and a second implant  300  is provided on the facing condyle. The implants may be installed such that the implants present each other mating surfaces (as illustrated), or not. For example, where the tibial implant  200  is placed in the medial compartment of the knee and the condyle implant  300  is placed in the lateral compartment. Other combinations are possible. Turning now to  FIG. 10D , a tibial implant  200  is provided along with a bicompartmental condyle implant  500 . As discussed above, these implants may or may not be associated with the same compartment of the knee joint. 
     The arthroplasty system can be designed to reflect aspects of the tibial shape, femoral shape and/or patellar shape. Tibial shape and femoral shape can include cartilage, bone or both. Moreover, the shape of the implant can also include portions or all components of other articular structures such as the menisci. The menisci are compressible, in particular during gait or loading. For this reason, the implant can be designed to incorporate aspects of the meniscal shape accounting for compression of the menisci during loading or physical activities. For example, the undersurface  204  of the implant  200  can be designed to match the shape of the tibial plateau including cartilage or bone or both. The superior surface  202  of the implant  200  can be a composite of the articular surface of the tibia (in particular in areas that are not covered by menisci) and the meniscus. Thus, the outer aspects of the device can be a reflection of meniscal height. Accounting for compression, this can be, for example, 20%, 40%, 60% or 80% of uncompressed meniscal height. 
     Similarly the superior surface  304  of the implant  300  can be designed to match the shape of the femoral condyle including cartilage or bone or both. The inferior surface  302  of the implant  300  can be a composite of the surface of the tibial plateau (in particular in areas that are not covered by menisci) and the meniscus. Thus, at least a portion of the outer aspects of the device can be a reflection of meniscal height. Accounting for compression, this can be, for example, 20%, 40%, 60% or 80% of uncompressed meniscal height. These same properties can be applied to the implants shown in  FIGS. 4-8 , as well. 
     In some embodiments, the outer aspect of the device reflecting the meniscal shape can be made of another, preferably compressible material. If a compressible material is selected it is preferably designed to substantially match the compressibility and biomechanical behavior of the meniscus. 
     The height and shape of the menisci for any joint surface to be repaired can be measured directly on an imaging test. If portions, or all, of the meniscus are torn, the meniscal height and shape can be derived from measurements of a contralateral joint or using measurements of other articular structures that can provide an estimate on meniscal dimensions. 
     In another embodiment, the superior face of the implants  300 ,  400  or  500  can be shaped according to the femur. The shape can preferably be derived from the movement patterns of the femur relative to the tibial plateau thereby accounting for variations in femoral shape and tibiofemoral contact area as the femoral condyle flexes, extends, rotates, translates and glides on the tibia and menisci. The movement patterns can be measured using any current or future test know in the art such as fluoroscopy, MRI, gait analysis and combinations thereof. 
     The arthroplasty can have two or more components, one essentially mating with the tibial surface and the other substantially articulating with the femoral component. The two components can have a flat opposing surface. Alternatively, the opposing surface can be curved. The curvature can be a reflection of the tibial shape, the femoral shape including during joint motion, and the meniscal shape and combinations thereof. 
     Wear pattern can be adjusted in any joint and for any type of replacement or resurfacing device. For example, wear patterns in hips, knees, ankles, elbows, shoulders, and spines can be adjusted and/or corrected. Similarly, various types of devices associated with repairs of such joints can be used. For example, a wear pattern in a knee can be adjusted and/or corrected in various types of knee devices, including, without limitation, interpositional devices, uni-compartmental and bicompartmental resurfacing devices, total resurfacing devices and total knee replacement devices. In cases where multiple contact points or wear patterns are identified in a joint, for example, wear patterns associated with both the medial and lateral femoral condyles in a total knee resurfacing, both can be corrected or improved. 
     The wear patterns can be adjusted to improve or reduce wear on a new device, such as a hip replacement or a uni-compartmental resurfacing device, to, for example, reduce wear on the device and increase the expected lifetime of the device. Additionally, wear patterns can be adjusted to improve the overall kinematics of the joint, for example, to alter the kinematics to an improved or even ideal case to improve the patient&#39;s overall motion in the joint. For example, a device can be designed for a knee joint that functions in a manner that increases wear and degradation of the joint such that the device, when implanted, alters the motion of the joint to a more ideal case with reduced wear and improved functionality. 
     When an orthopedic device is implanted into a joint, the wear pattern on the articular surface(s) can be altered and controlled. For example, when a unicompartmental knee resurfacing device is implanted in a knee, the wear pattern on the tibial articular surface between the tibia and femur can be changed such that the tibial articular surface functions differently after the implant is in place and the wear pattern at the articular surface is changed when compared to the wear pattern prior to surgery. Unlike existing off-the-shelf implants, which may change the wear pattern simply by virtue of introducing a new geometry into the joint, the wear pattern is changed by design based on the existing geometry and/or kinematics of a particular patient or set or class of patients. This allows the wear pattern to be controlled for that individual patient or for a class or set of patients that exhibit similar characteristic wear patterns, joint geometries and/or joint kinematics. Thus, for example, an improved wear pattern can be designed into a particular orthopedic implant that is specific to a single patient&#39;s anatomy, or the wear pattern can be altered based one or more designs from a library of designs that can be applied to one or more patients exhibiting a particular set of characteristics that meet predefined rules or other analyses. Further, the design can be based, at least in part, on the geometry of the joint, on the kinematics of the joint or on a combination thereof. 
       FIG. 11  illustrates in cross-section an embodiment for the hip featuring a wear pattern correcting resurfacing implant  1113  for a femoral head  1112  of femur  1111 . Implant  1113  features an inner surface  1116  which conforms, e.g., in a mirror image fashion, to the surface of femoral head  1112 . The outer surface of implant  1113  has a generally spherical curvature which matches that of acetabular component  1115  so as to permit a freedom of joint motion comparable to that of a normal hip joint. Inner surface  1116  features a wear pattern correcting surface  1114  that conforms to a wear pattern on femoral head  1112 . 
       FIGS. 12 and 13  illustrate in cross sectional view a glenoid member  1220  and  1320 .  FIGS. 12 and 13  are identical, save for the geometry of the bearing surface as discussed below.) Glenoid member  1220  includes an affixation surface  1242  for affixing the glenoid member  1220  to the scapula  1210 . An upper, or superior, affixation peg  1244  projects from the device and is integral with the glenoid member  1220 . Peg  1244  fits into hole  1260 . A lower, or inferior, affixation peg  1248  also projects from the glenoid member  1220  and is oriented in an offset direction, relative to the superior affixation peg  1244 . Peg  1248  fits into hole  1262 . The inferior affixation peg  1248  is integral with the glenoid member  1220 . Glenoid component  1212  may desirably be constructed in a one-piece member of synthetic polymeric material, e.g., ultra high molecular weight polyethylene (UHMWPE). Cement mantle  1278  affixes the glenoid component  1212  in place in the scapula  1210 . 
     Glenoid component  1212  includes a glenoid member  1220  extending in a superior-inferior direction, that is, in upward and downward directions, between an upper, or superior, edge  1222 , and a lower, or inferior, edge  1224 . An obverse, or lateral, face  1226  at the front of the glenoid member  1220  has a concave contour configuration and provides bearing means in the form of a concave bearing surface  1228  for receiving a humeral head. An aspect can be seen in  FIG. 12 , wherein the concavity of bearing surface  1228  has been adjusted inferiorly to match an inferior wear pattern on the humeral head. In  FIG. 13 , the concavity of bearing surface  1228  has been adjusted superiorly to match a superior wear pattern on the humeral head. 
       FIGS. 14-16  illustrate, in simplified coronal view, a tibia with medial ( FIG. 14 ), lateral ( FIG. 15 ) and central ( FIG. 16 ) lateral tibial plateau wear patterns, and a lateral tibial plateau implant featuring a wear pattern correcting bearing surface for each respective type of wear pattern. Tibia  1414  includes lateral tibial plateau  1413 , medial tibial plateau  1412 , and tibial spine  1411 . A medial wear pattern  1410  can be seen in the lateral tibial plateau  1413 . Device  1415  is an implant having a bearing surface  1418  based on patient-specific information and desirably derived from imaging data as described herein. In device  1415 , the concavity of bearing surface  1418  is adjusted medially to account for, and adapt to, the wear characteristics of this particular patient. Device  1415  also features integral keel  1416  and pegs  1417  (which are better seen in  FIGS. 17-19 .) 
     In  FIG. 15 , a lateral wear pattern  1510  can be seen in the lateral tibial plateau  1513 . Device  1515  is an implant having a bearing surface  1518  based on patient-specific information and desirably derived from imaging data as described herein. In device  1515 , the concavity of bearing surface  1518  is adjusted laterally to account for, and adapt to, the wear characteristics of this particular patient. 
     In  FIG. 16 , a central wear pattern  1610  can be seen in the lateral tibial plateau  1613 . Device  1615  is an implant having a bearing surface  1618  based on patient-specific information and desirably derived from imaging data as described herein. In device  1615 , the concavity of bearing surface  1618  is adjusted centrally to account for, and adapt to, the wear characteristics of this particular patient. 
       FIGS. 17-19  illustrate, in simplified sagittal view, a tibia with posterior ( FIG. 17 ), anterior ( FIG. 18 ) and central ( FIG. 19 ) lateral tibial plateau wear patterns, and a lateral tibial plateau implant featuring a wear pattern correcting bearing surface for each respective type of wear pattern. Tibia  1714  includes lateral tibial plateau  1713 , and tibial spine  1711 . A posterior wear pattern  1710  can be seen in the lateral tibial plateau  1713 . Device  1715  is an implant having a bearing surface  1718  based on patient-specific information and desirably derived from imaging data as described herein. In device  1715 , the concavity of bearing surface  1718  is adjusted posteriorly to account for, and adapt to, the wear characteristics of this particular patient. Device  1715  also features integral keel  1716  and pegs  1717 . 
     In  FIG. 18 , an anterior wear pattern  1810  can be seen in the lateral tibial plateau  1813 . Device  1815  is an implant having a bearing surface  1818  based on patient-specific information and desirably derived from imaging data as described herein. In device  1815 , the concavity of bearing surface  1818  is adjusted anteriorly to account for, and adapt to, the wear characteristics of this particular patient. 
     In  FIG. 19 , a central wear pattern  1910  can be seen in the lateral tibial plateau  1913 . Device  1915  is an implant having a bearing surface  1918  based on patient-specific information and desirably derived from imaging data as described herein. In device  1915 , the concavity of bearing surface  1918  is adjusted centrally to account for, and adapt to, the wear characteristics of this particular patient. 
     In the above embodiments, if desirable, the width of the concavity, e.g., in the tibial and glenoid components, may be widened to provide a less constraining arrangement if the wear pattern is wide. Alternately, if desirable, the width of the concavity, e.g., in the tibial and glenoid components, may be narrowed to provide a more constraining arrangement if wear pattern is narrow. 
     Various components and combinations of components can be used in devices that correct or adjust wear patters. Examples of single-component systems include plastics, polymers, metals, metal alloys, crystal free metals, biologic materials, or combinations thereof. In certain embodiments, the surface of the repair system facing the underlying bone can be smooth. In other embodiments, the surface of the repair system facing the underlying bone can be porous or porous-coated. In another aspect, the surface of the repair system facing the underlying bone is designed with one or more grooves, for example to facilitate the in-growth of the surrounding tissue. The external surface of the device can have a step-like design, which can be advantageous for altering biomechanical stresses. Optionally, flanges can also be added at one or more positions on the device (e.g., to prevent the repair system from rotating, to control toggle and/or prevent settling into the marrow cavity). The flanges can be part of a conical or a cylindrical design. A portion or all of the repair system facing the underlying bone can also be flat which can help to control depth of the implant and to prevent toggle. 
     Examples of multiple-component systems include combinations of metals, plastics, metal alloys, crystal free metals, and biological materials. One or more components of the articular surface repair system can be composed of a biologic material (e.g., a tissue scaffold with cells such as cartilage cells or stem cells alone or seeded within a substrate such as a bioresorbable material or a tissue scaffold, allograft, autograft or combinations thereof) and/or a non-biological material (e.g., polyethylene or a chromium alloy such as chromium cobalt). 
     Thus, the repair system can include one or more areas of a single material or a combination of materials, for example, the articular surface repair system can have a first and a second component. The first component is typically designed to have size, thickness and curvature similar to that of the cartilage tissue lost while the second component is typically designed to have a curvature similar to the subchondral bone. In addition, the first component can have biomechanical properties similar to articular cartilage, including but not limited to similar elasticity and resistance to axial loading or shear forces. The first and the second component can consist of two different metals or metal alloys. One or more components of the system (e.g., the second portion) can be composed of a biologic material including bone or a non-biologic material, e.g., hydroxyapatite, tantalum, chromium alloys, chromium cobalt or other metal alloys. 
     One or more regions of the articular surface repair system (e.g., the outer margin of the first portion and/or the second portion) can be bioresorbable, for example to allow the interface between the articular surface repair system and the patient&#39;s normal cartilage, over time, to be filled in with hyaline or fibrocartilage. Similarly, one or more regions (e.g., the outer margin of the first portion of the articular surface repair system and/or the second portion) can be porous. The degree of porosity can change throughout the porous region, linearly or non-linearly, for where the degree of porosity will typically decrease towards the center of the articular surface repair system. The pores can be designed for in-growth of cartilage cells, cartilage matrix, and connective tissue thereby achieving a smooth interface between the articular surface repair system and the surrounding cartilage. 
     The repair system (e.g., the second component in multiple component systems) can be attached to the patient&#39;s bone with use of a cement-like material such as methylmethacrylate, injectable hydroxy- or calcium-apatite materials and the like. 
     In certain embodiments, one or more portions of the articular surface repair system can be pliable or liquid or deformable at the time of implantation and can harden later. Hardening can occur, for example, within 1 second to 2 hours (or any time period therebetween), preferably with in 1 second to 30 minutes (or any time period therebetween), more preferably between 1 second and 10 minutes (or any time period therebetween). 
     One or more components of the articular surface repair system can be adapted to receive injections. For example, the external surface of the articular surface repair system can have one or more openings therein. The openings can be sized to receive screws, tubing, needles or other devices which can be inserted and advanced to the desired depth, for example, through the articular surface repair system into the marrow space. Injectables such as methylmethacrylate and injectable hydroxy- or calcium-apatite materials can then be introduced through the opening (or tubing inserted therethrough) into the marrow space thereby bonding the articular surface repair system with the marrow space. Similarly, screws or pins, or other anchoring mechanisms can be inserted into the openings and advanced to the underlying subchondral bone and the bone marrow or epiphysis to achieve fixation of the articular surface repair system to the bone. Portions or all components of the screw or pin can be bioresorbable, for example, the distal portion of a screw that protrudes into the marrow space can be bioresorbable. During the initial period after the surgery, the screw can provide the primary fixation of the articular surface repair system. Subsequently, ingrowth of bone into a porous-coated area along the undersurface of the articular cartilage repair system can take over as the primary stabilizer of the articular surface repair system against the bone. 
     The articular surface repair system can be anchored to the patient&#39;s bone with use of a pin or screw or other attachment mechanism. The attachment mechanism can be bioresorbable. The screw or pin or attachment mechanism can be inserted and advanced towards the articular surface repair system from a non-cartilage covered portion of the bone or from a non-weight-bearing surface of the joint. 
     The interface between the articular surface repair system and the surrounding normal cartilage can be at an angle, for example oriented at an angle of 90 degrees relative to the underlying subchondral bone. Suitable angles can be determined in view of the teachings herein, and in certain cases, non-90 degree angles can have advantages with regard to load distribution along the interface between the articular surface repair system and the surrounding normal cartilage. 
     The interface between the articular surface repair system and the surrounding normal cartilage and/or bone can be covered with a pharmaceutical or bioactive agent, for example a material that stimulates the biological integration of the repair system into the normal cartilage and/or bone. The surface area of the interface can be irregular, for example, to increase exposure of the interface to pharmaceutical or bioactive agents. 
     D. Pre-Existing Repair Systems 
     As described herein, repair systems of various sizes, curvatures and thicknesses can be obtained. These repair systems can be catalogued and stored to create a library of systems from which an appropriate system for an individual patient can then be selected. In other words, a defect, or an articular surface, is assessed in a particular subject and a pre-existing repair system having a suitable shape and size is selected from the library for further manipulation (e.g., shaping) and implantation. 
     E. Mini-Prosthesis 
     The methods and compositions described herein can be used to replace only a portion of the articular surface, for example, an area of diseased cartilage or lost cartilage on the articular surface. In these systems, the articular surface repair system can be designed to replace only the area of diseased or lost cartilage or it can extend beyond the area of diseased or lost cartilage, e.g., 3 or 5 mm into normal adjacent cartilage. In certain embodiments, the prosthesis replaces less than about 70% to 80% (or any value therebetween) of the articular surface (e.g., any given articular surface such as a single femoral condyle, etc.), preferably, less than about 50% to 70% (or any value therebetween), more preferably, less than about 30% to 50% (or any value therebetween), more preferably less than about 20% to 30% (or any value therebetween), even more preferably less than about 20% of the articular surface. 
     The prosthesis can include multiple components, for example a component that is implanted into the bone (e.g., a metallic device) attached to a component that is shaped to cover the defect of the cartilage overlaying the bone. Additional components, for example intermediate plates, meniscal repair systems and the like can also be included. It is contemplated that each component replaces less than all of the corresponding articular surface. However, each component need not replace the same portion of the articular surface. In other words, the prosthesis can have a bone-implanted component that replaces less than 30% of the bone and a cartilage component that replaces 60% of the cartilage. The prosthesis can include any combination, provided each component replaces less than the entire articular surface. 
     The articular surface repair system can be formed or selected so that it will achieve a near anatomic fit or match with the surrounding or adjacent cartilage or bone. Typically, the articular surface repair system is formed and/or selected so that its outer margin located at the external surface will be aligned with the surrounding or adjacent cartilage. 
     Thus, the articular repair system can be designed to replace the weight-bearing portion (or more or less than the weight bearing portion) of an articular surface, for example in a femoral condyle. The weight-bearing surface refers to the contact area between two opposing articular surfaces during activities of normal daily living (e.g., normal gait). At least one or more weight-bearing portions can be replaced in this manner, e.g., on a femoral condyle and on a tibia. 
     In other embodiments, an area of diseased cartilage or cartilage loss can be identified in a weight-bearing area and only a portion of the weight-bearing area, specifically the portion containing the diseased cartilage or area of cartilage loss, can be replaced with an articular surface repair system. 
     In another embodiment, the articular repair system can be designed or selected to replace substantially the entire articular surface, e.g., a condyle. 
     In another embodiment, for example, in patients with diffuse cartilage loss, the articular repair system can be designed to replace an area slightly larger than the weight-bearing surface. 
     In certain aspects, the defect to be repaired is located only on one articular surface, typically the most diseased surface. For example, in a patient with severe cartilage loss in the medial femoral condyle but less severe disease in the tibia, the articular surface repair system can only be applied to the medial femoral condyle. Preferably, in any methods described herein, the articular surface repair system is designed to achieve an exact or a near anatomic fit with the adjacent normal cartilage. 
     In other embodiments, more than one articular surface can be repaired. The area(s) of repair will be typically limited to areas of diseased cartilage or cartilage loss or areas slightly greater than the area of diseased cartilage or cartilage loss within the weight-bearing surface(s). 
     In another embodiment, one or more components of the articular surface repair (e.g., the surface of the system that is pointing towards the underlying bone or bone marrow) can be porous or porous-coated. A variety of different porous metal coatings have been proposed for enhancing fixation of a metallic prosthesis by bone tissue in-growth. Thus, for example, U.S. Pat. No. 3,855,638, discloses a surgical prosthetic device, which can be used as a bone prosthesis, comprising a composite structure consisting of a solid metallic material substrate and a porous coating of the same solid metallic material adhered to and extending over at least a portion of the surface of the substrate. The porous coating consists of a plurality of small discrete particles of metallic material bonded together at their points of contact with each other to define a plurality of connected interstitial pores in the coating. The size and spacing of the particles, which can be distributed in a plurality of monolayers, can be such that the average interstitial pore size is not more than about 200 microns. Additionally, the pore size distribution can be substantially uniform from the substrate-coating interface to the surface of the coating. In another embodiment, the articular surface repair system can contain one or more polymeric materials that can be loaded with and release therapeutic agents including drugs or other pharmacological treatments that can be used for drug delivery. The polymeric materials can, for example, be placed inside areas of porous coating. The polymeric materials can be used to release therapeutic drugs, e.g., bone or cartilage growth stimulating drugs. This embodiment can be combined with other embodiments, wherein portions of the articular surface repair system can be bioresorbable. For example, the first layer of an articular surface repair system or portions of its first layer can be bioresorbable. As the first layer gets increasingly resorbed, local release of a cartilage growth-stimulating drug can facilitate in-growth of cartilage cells and matrix formation. 
     In any of the methods or compositions described herein, the articular surface repair system can be pre-manufactured with a range of sizes, curvatures and thicknesses. Alternatively, the articular surface repair system can be custom-made for an individual patient. 
     IV. Manufacturing 
     A. Shaping 
     In certain instances shaping of the repair material will be required before or after formation (e.g., growth to desired thickness), for example where the thickness of the required cartilage material is not uniform (e.g., where different sections of the cartilage replacement or regenerating material require different thicknesses). 
     The replacement material can be shaped by any suitable technique including, but not limited to, casting techniques, mechanical abrasion, laser abrasion or ablation, radiofrequency treatment, cryoablation, variations in exposure time and concentration of nutrients, enzymes or growth factors and any other means suitable for influencing or changing cartilage thickness. See, e.g., WO 00/15153. If enzymatic digestion is used, certain sections of the cartilage replacement or regenerating material can be exposed to higher doses of the enzyme or can be exposed longer as a means of achieving different thicknesses and curvatures of the cartilage replacement or regenerating material in different sections of said material. 
     The material can be shaped manually and/or automatically, for example using a device into which a pre-selected thickness and/or curvature has been input and then programming the device using the input information to achieve the desired shape. 
     In addition to, or instead of, shaping the cartilage repair material, the site of implantation (e.g., bone surface, any cartilage material remaining, etc.) can also be shaped by any suitable technique in order to enhance integration of the repair material. 
     B. Sizing 
     The articular repair system can be formed or selected so that it will achieve a near anatomic fit or match with the surrounding or adjacent cartilage, subchondral bone, menisci and/or other tissue. The shape of the repair system can be based on an imaging analysis. If the articular repair system is intended to replace an area of diseased cartilage or lost cartilage, the near anatomic fit can be achieved using a method that provides a virtual reconstruction of the shape of healthy cartilage in an electronic image or reflect or conform to a wear pattern. An imaging analysis may include conventional and digital imaging techniques known in the art, including x-ray imaging and processing; fluoroscopy; digital tomosynthesis; ultrasound including A-scan, B-scan and C-scan, optical coherence, conventional, cone beam, or spiral computed tomography (CT); single photon emission tomography (SPECT); bone scan; positron emission tomography (PET); magnetic resonance imaging (MRI); thermal imaging; and optical imaging, or a combination thereof. Such techniques are explained fully in the literature and need not be described herein. See, e.g.,  X - Ray Structure Determination: A Practical Guide,  2nd Ed., Stout et al., eds. Wiley &amp; Sons, 1989 ; Body CT: A Practical Approach , Slone, ed., McGraw-Hill 1999 ; X - ray Diagnosis: A Physician&#39;s Approach , Lam, ed., Springer-Verlag 1998 ; Dental Radiology: Understanding the X - Ray Image , Brocklebank, ed., Oxford University Press 1997; and  The Essential Physics of Medical Imaging  (2 nd  Ed.), Bushberg et al. 
     In one embodiment, a near normal cartilage surface at the position of the cartilage defect can be reconstructed by interpolating the healthy cartilage surface across the cartilage defect or area of diseased cartilage. This can, for example, be achieved by describing the healthy cartilage by means of a parametric surface (e.g., a B-spline surface), for which the control points are placed such that the parametric surface follows the contour of the healthy cartilage and bridges the cartilage defect or area of diseased cartilage. The continuity properties of the parametric surface will provide a smooth integration of the part that bridges the cartilage defect or area of diseased cartilage with the contour of the surrounding healthy cartilage. The part of the parametric surface over the area of the cartilage defect or area of diseased cartilage can be used to determine the shape or part of the shape of the articular repair system to match with the surrounding cartilage. 
     In another embodiment, a near normal cartilage surface at the position of the cartilage defect or area of diseased cartilage can be reconstructed using morphological image processing. In a first step, the cartilage can be extracted from the electronic image using manual, semi-automated and/or automated segmentation techniques (e.g., manual tracing, region growing, live wire, model-based segmentation), resulting in a binary image. Defects in the cartilage appear as indentations that can be filled with a morphological closing operation performed in 2-D or 3-D with an appropriately selected structuring element. The closing operation is typically defined as a dilation followed by an erosion. A dilation operator sets the current pixel in the output image to 1 if at least one pixel of the structuring element lies inside a region in the source image. An erosion operator sets the current pixel in the output image to 1 if the whole structuring element lies inside a region in the source image. The filling of the cartilage defect or area of diseased cartilage creates a new surface over the area of the cartilage defect or area of diseased cartilage that can be used to determine the shape or part of the shape of the articular repair system to match with the surrounding cartilage or subchondral bone. 
     As described above, the articular repair system can be formed or selected from a library or database of systems of various sizes, curvatures and thicknesses so that it will achieve a near anatomic fit or match with the surrounding or adjacent cartilage and/or subchondral bone. These systems can be pre-made or made to order for an individual patient. In order to control the fit or match of the articular repair system with the surrounding or adjacent cartilage or subchondral bone or menisci and other tissues preoperatively, a software program can be used that projects the articular repair system over the anatomic position where it will be implanted. Suitable software is commercially available and/or readily modified or designed by a skilled programmer. 
     In yet another embodiment, the articular surface repair system can be projected over the implantation site using one or more 3-D images. The cartilage and/or subchondral bone and other anatomic structures are extracted from a 3-D electronic image such as an MRI or a CT using manual, semi-automated and/or automated segmentation techniques. A 3-D representation of the cartilage and/or subchondral bone and other anatomic structures as well as the articular repair system is generated, for example using a polygon or NURBS surface or other parametric surface representation. For a description of various parametric surface representations see, for example Foley, J. D. et al., Computer Graphics: Principles and Practice in C; Addison-Wesley, 2 nd  edition, 1995. 
     The 3-D representations of the cartilage and/or subchondral bone and other anatomic structures and the articular repair system can be merged into a common coordinate system. The articular repair system can then be placed at the desired implantation site. The representations of the cartilage, subchondral bone, menisci and other anatomic structures and the articular repair system are rendered into a 3-D image, for example application programming interfaces (APIs) OpenGL® (standard library of advanced 3-D graphics functions developed by SGI, Inc.; available as part of the drivers for PC-based video cards, for example from www.nvidia.com for NVIDIA video cards orati.amd.com for ATI/AMD products) or DirectX® (multimedia API for Microsoft Windows® based PC systems; available from www.microsoft.com). The 3-D image can be rendered showing the cartilage, subchondral bone, menisci or other anatomic objects, and the articular repair system from varying angles, e.g., by rotating or moving them interactively or non-interactively, in real-time or non-real-time. 
     The software can be designed so that the articular repair system, including surgical tools and instruments with the best fit relative to the cartilage and/or subchondral bone is automatically selected, for example using some of the techniques described above. Alternatively, the operator can select an articular repair system, including surgical tools and instruments and project it or drag it onto the implantation site using suitable tools and techniques. The operator can move and rotate the articular repair systems in three dimensions relative to the implantation site and can perform a visual inspection of the fit between the articular repair system and the implantation site. The visual inspection can be computer assisted. The procedure can be repeated until a satisfactory fit has been achieved. The procedure can be performed manually by the operator; or it can be computer-assisted in whole or part. For example, the software can select a first trial implant that the operator can test. The operator can evaluate the fit. The software can be designed and used to highlight areas of poor alignment between the implant and the surrounding cartilage or subchondral bone or menisci or other tissues. Based on this information, the software or the operator can then select another implant and test its alignment. One of skill in the art will readily be able to select, modify and/or create suitable computer programs for the purposes described herein. 
     In another embodiment, the implantation site can be visualized using one or more cross-sectional 2-D images. Typically, a series of 2-D cross-sectional images will be used. The articular repair system can then be superimposed onto one or more of these 2-D images. The 2-D cross-sectional images can be reconstructed in other planes, e.g., from sagittal to coronal, etc. Isotropic data sets (e.g., data sets where the slice thickness is the same or nearly the same as the in-plane resolution) or near isotropic data sets can also be used. Multiple planes can be displayed simultaneously, for example using a split screen display. The operator can also scroll through the 2-D images in any desired orientation in real time or near real time; the operator can rotate the imaged tissue volume while doing this. The articular repair system can be displayed in cross-section utilizing different display planes, e.g., sagittal, coronal or axial, typically matching those of the 2-D images demonstrating the cartilage, subchondral bone, menisci or other tissue. Alternatively, a three-dimensional display can be used for the articular repair system. The 2-D electronic image and the 2-D or 3-D representation of the articular repair system can be merged into a common coordinate system. The articular repair system can then be placed at the desired implantation site. The series of 2-D cross-sections of the anatomic structures, the implantation site and the articular repair system can be displayed interactively (e.g., the operator can scroll through a series of slices) or non-interactively (e.g., as an animation that moves through the series of slices), in real-time or non-real-time. 
     C. Rapid Prototyping 
     Rapid prototyping is a technique for fabricating a three-dimensional object from a computer model of the object. A special printer is used to fabricate the prototype from a plurality of two-dimensional layers. Computer software sections the representations of the object into a plurality of distinct two-dimensional layers and then a three-dimensional printer fabricates a layer of material for each layer sectioned by the software. Together the various fabricated layers form the desired prototype. More information about rapid prototyping techniques is available in U.S. Publication No. 2002/0079601A1. An advantage to using rapid prototyping is that it enables the use of free form fabrication techniques that use toxic or potent compounds safely. These compounds can be safely incorporated in an excipient envelope, which reduces worker exposure 
     A powder piston and build bed are provided. Powder includes any material (metal, plastic, etc.) that can be made into a powder or bonded with a liquid. The power is rolled from a feeder source with a spreader onto a surface of a bed. The thickness of the layer is controlled by the computer. The print head then deposits a binder fluid onto the powder layer at a location where it is desired that the powder bind. Powder is again rolled into the build bed and the process is repeated, with the binding fluid deposition being controlled at each layer to correspond to the three-dimensional location of the device formation. For a further discussion of this process see, e.g., U.S. Patent Publication No. 2003/017365A1. 
     The rapid prototyping can use the two dimensional images obtained, as described above, to determine each of the two-dimensional shapes for each of the layers of the prototyping machine. In this scenario, each two dimensional image slice would correspond to a two-dimensional prototype slide. Alternatively, the three-dimensional shape of the defect can be determined, as described above, and then broken down into two dimensional slices for the rapid prototyping process. The advantage of using the three-dimensional model is that the two-dimensional slices used for the rapid prototyping machine can be along the same plane as the two-dimensional images taken or along a different plane altogether. 
     Rapid prototyping can be combined or used in conjunction with casting techniques. For example, a shell or container with inner dimensions corresponding to an articular repair system can be made using rapid prototyping. Plastic or wax-like materials are typically used for this purpose. The inside of the container can subsequently be coated, for example with a ceramic, for subsequent casting. Using this process, personalized casts can be generated. 
     Rapid prototyping can be used for producing articular repair systems. Rapid prototyping can be performed at a manufacturing facility. Alternatively, it may be performed in the operating room after an intraoperative measurement has been performed. 
     Wear pattern-specific implant shapes or geometries can be achieved using a number of different manufacturing techniques known in the art, including polishing, milling, machining, casting, rapid protocasting, laser sintering, laser melting and electro abrasion. In one embodiment, the wear pattern-adapted articular surface may be formed de novo. In another embodiment, the wear pattern-adapted articular surface may be formed by processing an implant with a standard shape of the articular surface (a “blank”) and adapting the shape for the particular wear pattern, e.g., using machining or electroabrasion. 
     V. Surgical Techniques 
     Prior to performing surgery on a patient, the surgeon can preoperatively make a determination of the alignment of the knee using, for example, an erect AP x-ray. In performing preoperative assessment any lateral and patella spurs that are present can be identified. 
     Using standard surgical techniques, the patient is anesthetized and an incision is made in order to provide access to the portion or portions of the knee joint to be repaired. A medial portal can be used initially to enable arthroscopy of the joint. Thereafter, the medial portal can be incorporated into the operative incision and/or standard lateral portals can be used. 
     Once an appropriate incision has been made, the exposed compartment is inspected for integrity, including the integrity of the ligament structures. If necessary, portions of the meniscus can be removed as well as any spurs or osteophytes that were identified in the AP x-ray or that may be present within the joint. In order to facilitate removal of osteophytes, the surgeon may flex the knee to gain exposure to additional medial and medial-posterior osteophytes. Additionally, osteophytes can be removed from the patella during this process. If necessary, the medial and/or lateral meniscus can also be removed at this point, if desired, along with the rim of the meniscus. 
     As would be appreciated by those of skill in the art, evaluation of the medial cruciate ligament may be required to facilitate tibial osteophyte removal. 
     Once the joint surfaces have been prepared, the desired implants can be inserted into the joint. 
     A. Tibial Plateau 
     To insert the device  200  of  FIG. 2  into the medial compartment, a mini-incision arthrotomy medial to the patella tendon is made. Once the incision is made, the medial condyle is exposed and a medial sleeve is prepared to about 1 cm below the joint line using a suitable knife and curved osteotome. After preparing the medial sleeve, a Z-retractor is placed around the medial tibial plateau and anterior portions of the meniscus and the osteophytes along the tibia and femur are removed. At this point, the knee should be flexed to about 60° or more. The Z-retractor is removed and the implant is placed against the most distal aspect of the femur and over the tibial plateau edge. The implant should be pushed straight back. In some instances, application of valgus stress may ease insertion of the implant. 
     To insert the device of  FIG. 2  into the lateral compartment a mini-incision arthrotomy is performed lateral to the patella tendon. Once the incision is made, the lateral condyle is exposed and a lateral sleeve is prepared to about 1 cm below the joint line using a suitable knife and curved osteotome. After preparing the lateral sleeve, a Z-retractor is placed around the lateral tibial plateau and anterior portions of the meniscus and the osteophytes along the tibia and femur are removed. The Z-retractor is removed and the implant is placed against the distal aspect of the femur and over the tibial plateau edge. The implant is held at a 45° angle and rotated against the lateral condyle using a lateral to medial push toward the lateral spine. In some instances, application of varus stress may ease insertion of the implant. 
     Once any implant shown in  FIG. 2  is implanted, the device should be positioned within 0 to 2 mm of the AP boundaries of the tibial plateau and superimposed over the boundary. Verification of the range of motion should then be performed to confirm that there is minimal translation of the implant. Once positioning is confirmed, closure of the wound is performed using techniques known in the art. 
     As will be appreciated, additional treatment of the surface of the tibial plateau may be desirable, depending on the configuration of the implant  200 . For example, one or more channels or grooves may be formed on the surface of the tibial plateau to accommodate anchoring mechanisms such as the keel  212  shown in  FIG. 2K  or the translational movement cross-members  222 ,  221  shown in  FIGS. 2M-N . 
     B. Condylar Repair Systems 
     To insert the device  300  shown in  FIG. 3 , depending on the condyle to be repaired either an antero-medial or antero-lateral skin incision is made which begins approximately 1 cm proximal to the superior border of the patella. The incision typically can range from, for example, 6-10 cm along the edge of the patella. As will be appreciated, a longer incision may be required under some circumstances. 
     It may be required to excise excess deep synovium to improve access to the joint. Additionally, all or part of the fat pad may also be excused and to enable inspection of the opposite joint compartment. Typically, osteophytes are removed from the entire medial and/or lateral edge of the femur and the tibia as well as any osteophytes on the edge of the patella that might be significant. 
     Although it is possible, typically the devices  300  do not require resection of the distal femur prior to implanting the device. However, if desired, bone cuts can be performed to provide a surface for the implant. 
     At this juncture, the patient&#39;s leg is placed in 90° flexion position. A guide can then be placed on the condyle which covers the distal femoral cartilage. The guide enables the surgeon to determine placement of apertures that enable the implant  300  to be accurately placed on the condyle. With the guide in place, holes are drilled into the condyle to create apertures from 1-3 mm in depth. Once the apertures have been created, the guide is removed and the implant  300  is installed on the surface of the condyle. Cement can be used to facilitate adherence of the implant  300  to the condyle. 
     Where more than one condyle is to be repaired, e.g., using two implants  300  of  FIG. 3 , or the implant  400  of  FIG. 4 , or where a condyle and a portion of the patellar surface is to be repaired, e.g., using the implant  500  of  FIG. 5 , the surgical technique described herein would be modified to, for example, provide a greater incision for accessing the joint, provide additional apertures for receiving the pegs of the implant, etc. 
     C. Patellar Repair System 
     To insert the device shown in  FIG. 7 , it may be appropriate to use the incisions made laterally or medially to the patella tendon and described above with respect to  FIG. 2 . First the patella is everted laterally and the fat pad and synovium are bent back from around the periphery of the patella. If desired, osteophytes can be removed. Prior to resurfacing the natural patella  620 , the knee should be manually taken through several ranges of motion maneuvers to determine whether subluxation is present. If subluxation is present, then it may be necessary to medialize the implant  600 . The natural patella can then be cut in a planar, or flat, manner such that a flat surface is presented to the implant. The geometric center of the patella  620  is then typically aligned with the geometric center of the implant  600 . In order to anchor the implant  600  to the patella  620 , one or more holes or apertures can be created in the patellar surface to accept the pegs  610  of the implant  600 . 
     VI. Kits 
     One ore more of the implants described above can be combined together in a kit such that the surgeon can select one or more implants to be used during surgery. 
     This description is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and the generic principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope as defined by the appended claims. The application of the concepts and principals extends beyond the specific embodiments described herein, which can be modified to suit particular uses contemplated, and entirely different embodiments are possible that will employ some or all of the principles described and have some, all or different advantages than those described herein. Methods recited herein may be carried out in any order of the recited events which is logically possible, as well as the recited order of events. Where a range of values is provided, it is understood that every intervening value, between the upper and lower limit of that range and any other stated or intervening value in that stated range is encompassed. Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein. To the extent necessary to achieve a complete understanding disclosed, the specification and drawings of all issued patents, patent publications, and patent applications cited in this application are incorporated herein by reference.