Patent Publication Number: US-2017367833-A1

Title: Cruciate retaining knee implants and methods for implanting cruciate retaining knee implants

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims priority from U.S. Patent Application No. 62/091,974 filed Dec. 15, 2014. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH 
     Not Applicable. 
     FIELD OF INVENTION 
     The present invention relates to cruciate ligament retaining knee implants, and instruments and methods for implanting cruciate ligament retaining knee implants. 
     BACKGROUND OF INVENTION 
     Implants used for knee replacement surgery generally comprise one or more femoral components  111 ,  121 ,  131  and one or more tibial components (see  FIGS. 1A-1C ). A tibial component in turn may be composed of tibial baseplate/s and tibial insert/s affixed to the tibial baseplate/s. In knee replacement surgery aiming to retain the anterior cruciate ligament (ACL), the tibial component can take the form of a unicompartmental (Uni— FIG. 1A ) implant  110  having a tibial baseplate  112  and a tibial insert  113  that replace one compartment of the native tibia (e.g. medial or lateral); a bi-unicompartmental (Bi-Uni— FIG. 1B ) implant  120  composed of two Uni implants  122 ,  124  having tibial baseplates  127 , 129  and tibial inserts  126 ,  128  that replace both medial and lateral compartments of the native tibia; or a Bi-Cruciate (BCR— FIG. 1C ) implant  130  composed of a tibial component  132  that replaces both compartments of the native tibia. The BCR tibial component  132  is generally composed of a single-piece tibial baseplate with an anterior-bridge  134  connecting the medial compartment  135  and the lateral compartment  136  of the tibial baseplate, and two tibial inserts  137 ,  138  affixed to the medial and lateral compartments of the tibial baseplate. In some BCR implants, the tibial insert may also be single-piece, with an anterior-bridge connecting the respective medial and lateral compartments. 
     The preservation of the ACL allows these implants to better restore the normal motion patterns (kinematics) of the knee following surgery, compared to ACL sacrificing implants. Nonetheless, kinematics of the native knee are not fully restored with these implants. When both medial and lateral compartments of the native tibia are to be replaced, a Bi-Uni or BCR tibial implant component may be used. The advantages of a Bi-Uni tibial implant relative to a BCR tibial implant is that is allows greater flexibility in positioning the medial/lateral tibial components according to the native anatomy of the medial and lateral compartments of the native tibia. However, this flexibility raises the challenge of accurately placing the medial and lateral tibial components relative to each other. The advantage of a BCR implant is that, since a single-piece tibial component (insert and/or baseplate) is used, the relative position of the medial and lateral compartments is maintained and joint loads can be shared between the medial and lateral tibial components. However, the use of a single-piece component requires removal of bone from the anterior region of the tibial eminence to accommodate the anterior-bridge of the BCR tibial implant ( FIG. 1C ). Further, the ability to match the native anatomy of the medial and lateral compartments of the native tibia is limited. 
     Accordingly, there remains a need for improved knee implants and instruments to enable accurate placement of knee implants. 
     SUMMARY 
     The present invention relates to cruciate ligament retaining knee implants, instruments and methods for implanting cruciate ligament retaining knee implants. 
     In one aspect, the invention provides an orthopedic implant having a femoral implant. The femoral implant includes one or both of a medial condyle and a lateral condyle. At least one of the medial condyle and the lateral condyle has a surface region joining a mesial edge and a femur-facing inner surface of the medial condyle or the lateral condyle. The surface region, when viewed in a plane transversely extending from an outer articular surface to the inner surface of the medial condyle or the lateral condyle, has a concave, convex, or chamfered geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant which includes a femoral implant including a medial condyle. A surface region joins a mesial edge and a femur-facing inner surface of the medial condyle. The surface region, when viewed in a plane transversely extending from an outer articular surface to the inner surface of the medial condyle, has a concave, convex, or chamfered geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant that includes a femoral implant having a lateral condyle. A surface region that joins a mesial edge and a femur-facing inner surface of the lateral condyle. The surface region, when viewed in a plane transversely extending from an outer articular surface to the inner surface of the lateral condyle, has a concave, convex, or chamfered geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-unicompartmental implant configured to replace both medial and lateral compartments of a native tibia. The bi-unicompartmental implant includes the femoral implant which includes a medial condyle and a lateral condyle. A surface region joins a mesial edge and a femur-facing inner surface of the medial condyle. The surface region, when viewed in a plane transversely extending from an outer articular surface to the inner surface of the medial condyle, has a concave, convex, or chamfered geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-unicompartmental implant configured to replace both medial and lateral compartments of a native tibia. The bi-unicompartmental implant includes a femoral implant which includes a medial condyle and a lateral condyle. A surface region joins a mesial edge and a femur-facing inner surface of the lateral condyle. The surface region, when viewed in a plane transversely extending from an outer articular surface to the inner surface of the lateral condyle, has a concave, convex, or chamfered geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-unicompartmental implant configured to replace both medial and lateral compartments of a native tibia. The bi-unicompartmental implant includes a femoral implant which includes a medial condyle and a lateral condyle. A surface region joins a mesial edge and a femur-facing inner surface of the medial condyle. The surface region, when viewed in a plane transversely extending from an outer articular surface to the inner surface of the medial condyle, has a concave, convex, or chamfered geometry. A second surface region joins a mesial edge and a femur-facing inner surface of the lateral condyle. The surface region, when viewed in a plane transversely extending from an outer articular surface to the inner surface of the lateral condyle, has a concave, convex, or chamfered geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-cruciate implant configured to replace both medial and lateral compartments of a native tibia. The bi-cruciate implant includes a femoral implant that includes a medial condyle and a lateral condyle. A surface region joins a mesial edge and a femur-facing inner surface of the medial condyle. The surface region, when viewed in a plane transversely extending from an outer articular surface to the inner surface of the medial condyle, has a concave, convex, or chamfered geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-cruciate implant configured to replace both medial and lateral compartments of a native tibia. The bi-cruciate implant includes a femoral implant that includes a medial condyle and a lateral condyle. A surface region joins a mesial edge and a femur-facing inner surface of the lateral condyle. The surface region, when viewed in a plane transversely extending from an outer articular surface to the inner surface of the lateral condyle, has a concave, convex, or chamfered geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-cruciate implant configured to replace both medial and lateral compartments of a native tibia. The bi-cruciate implant includes a femoral implant that includes a medial condyle and a lateral condyle. A surface region joins a mesial edge and a femur-facing inner surface of the medial condyle. The surface region, when viewed in a plane transversely extending from an outer articular surface to the inner surface of the medial condyle, has a concave, convex, or chamfered geometry. A second surface region joins a mesial edge and a femur-facing inner surface of the lateral condyle. The surface region, when viewed in a plane transversely extending from an outer articular surface to the inner surface of the lateral condyle, has a concave, convex, or chamfered geometry. 
     In one version of this aspect of the invention, the surface region, when viewed in the plane, has a straight line profile. 
     In one version of this aspect of the invention, the surface region, when viewed in the plane, has a concave curvilinear profile. 
     In one version of this aspect of the invention, the surface region, when viewed in the plane, has a convex curvilinear profile. 
     In one version of this aspect of the invention, the surface region, when viewed in the plane, has a concave profile includes a plurality of connected line segments. 
     In one version of this aspect of the invention, a distance, measured perpendicularly from the inner surface to a normal line to a junction of the surface region and the mesial edge, is in a range of range 0.5 to 7 millimeters. 
     In one version of this aspect of the invention, a distance, measured perpendicularly from the mesial edge to a normal line to a junction of the surface region and the inner surface, is in a range of range 0.5 to 7 millimeters. 
     In another aspect, the invention provides an orthopedic implant. The orthopedic implant includes a femoral implant including one or both of a medial condyle and a lateral condyle. At least one of the medial condyle and the lateral condyle is configured such that a posterior thickness and/or a posterodistal condyle thickness of the medial condyle or the lateral condyle is less than a distal condyle thickness of the medial condyle or the lateral condyle. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant that includes a femoral implant including a medial condyle. The medial condyle is configured such that a posterior thickness and/or a posterodistal condyle thickness of the medial condyle is less than a distal condyle thickness of the medial condyle. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant that includes a femoral implant including a lateral condyle. The lateral condyle is configured such that a posterior thickness and/or a posterodistal condyle thickness of the lateral condyle is less than a distal condyle thickness of the lateral condyle. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-unicompartmental implant configured to replace both medial and lateral compartments of a native tibia. The bi-unicompartmental implant includes a femoral implant including a medial condyle and a lateral condyle. The medial condyle is configured such that a posterior thickness and/or a posterodistal condyle thickness of the medial condyle is less than a distal condyle thickness of the medial condyle. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-unicompartmental implant configured to replace both medial and lateral compartments of a native tibia. The bi-unicompartmental implant includes a femoral implant including a medial condyle and a lateral condyle. The lateral condyle is configured such that a posterior thickness and/or a posterodistal condyle thickness of the lateral condyle is less than a distal condyle thickness of the lateral condyle. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-unicompartmental implant configured to replace both medial and lateral compartments of a native tibia. The bi-unicompartmental implant includes a femoral implant including a medial condyle and a lateral condyle. The medial condyle is configured such that a posterior thickness and/or a posterodistal condyle thickness of the medial condyle is less than a distal condyle thickness of the medial condyle. The lateral condyle is configured such that a posterior thickness and/or a posterodistal condyle thickness of the lateral condyle is less than a distal condyle thickness of the lateral condyle. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-cruciate implant configured to replace both medial and lateral compartments of a native tibia. The bi-cruciate implant includes a femoral implant including a medial condyle and a lateral condyle. The medial condyle is configured such that a posterior thickness and/or a posterodistal condyle thickness of the medial condyle is less than a distal condyle thickness of the medial condyle. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-cruciate implant configured to replace both medial and lateral compartments of a native tibia. The bi-cruciate implant includes a femoral implant including a medial condyle and a lateral condyle. The lateral condyle is configured such that a posterior thickness and/or a posterodistal condyle thickness of the lateral condyle is less than a distal condyle thickness of the lateral condyle. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-cruciate implant configured to replace both medial and lateral compartments of a native tibia. The bi-cruciate implant includes a femoral implant including a medial condyle and a lateral condyle. The medial condyle is configured such that a posterior thickness and/or a posterodistal condyle thickness of the medial condyle is less than a distal condyle thickness of the medial condyle. The lateral condyle is configured such that a posterior thickness and/or a posterodistal condyle thickness of the lateral condyle is less than a distal condyle thickness of the lateral condyle. 
     In one version of this aspect of the invention, a posterior thickness of the medial condyle or the lateral condyle is less than a distal condyle thickness of the medial condyle or the lateral condyle. 
     In one version of this aspect of the invention, a posterodistal condyle thickness of the medial condyle or the lateral condyle is less than a distal condyle thickness of the medial condyle or the lateral condyle. 
     In one version of this aspect of the invention, a posterior thickness and a posterodistal condyle thickness of the medial condyle or the lateral condyle are less than a distal condyle thickness of the medial condyle or the lateral condyle. 
     In another aspect, the invention provides an orthopedic implant. The orthopedic implant includes a femoral implant including one or both of a medial condyle and a lateral condyle. The medial condyle and/or the lateral condyle is configured such that each of a posterior thickness, a posterodistal thickness, and a distal condyle thickness of the medial condyle or the lateral condyle is less than 8 millimeters. The medial condyle and/or the lateral condyle includes a reinforcing structure that extends away from the inner surface of the medial condyle or the lateral condyle. The reinforcing structure is configured to interface with femoral bone. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant that includes a femoral implant having a medial condyle. The medial condyle includes the reinforcing structure. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant that includes a femoral implant having a lateral condyle. The lateral condyle includes the reinforcing structure. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-unicompartmental implant configured to replace both medial and lateral compartments of a native tibia. The bi-unicompartmental implant includes a femoral implant having a medial condyle and a lateral condyle. The medial condyle includes the reinforcing structure. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-unicompartmental implant configured to replace both medial and lateral compartments of a native tibia. The bi-unicompartmental implant includes a femoral implant having a medial condyle and a lateral condyle. The lateral condyle includes the reinforcing structure. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-cruciate implant configured to replace both medial and lateral compartments of a native tibia. The bi-cruciate implant includes a femoral implant having a medial condyle and a lateral condyle. The medial condyle includes the reinforcing structure. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-cruciate implant configured to replace both medial and lateral compartments of a native tibia. The bi-cruciate implant includes a femoral implant having a medial condyle and a lateral condyle. The lateral condyle includes the reinforcing structure. 
     In one version of this aspect of the invention, the reinforcing structure comprises a rectangular fin. 
     In one version of this aspect of the invention, the reinforcing structure comprises a partially cylindrical fin. 
     In another aspect, the invention provides an orthopedic implant, wherein the orthopedic implant includes a tibial implant including one or both of a medial tibial component and a lateral tibial component. At least one of the medial tibial component and the lateral tibial component is configured such a surface region joining a mesial edge and a tibial-facing surface of the medial tibial component or the lateral tibial component has a rounded profile or a chamfered profile when viewed in a plane coronally extending from an outer edge of the medial tibial component or the lateral tibial component to the mesial edge of the medial tibial component or the lateral tibial component. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant that includes a tibial implant having a medial tibial component. A surface region joins a mesial edge and a tibial-facing surface of the medial tibial component. The surface region has a rounded profile or a chamfered profile when viewed in a plane coronally extending from an outer edge of the medial tibial component to the mesial edge of the medial tibial component. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant that includes a tibial implant having a lateral tibial component. A surface region joins a mesial edge and a tibial-facing surface of the lateral tibial component. The surface region has a rounded profile or a chamfered profile when viewed in a plane coronally extending from an outer edge of the lateral tibial component to the mesial edge of the lateral tibial component. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-unicompartmental implant configured to replace both medial and lateral compartments of a native tibia. The bi-unicompartmental implant includes a tibial implant having a medial tibial component and a lateral tibial component. A surface region joins a mesial edge and a tibial-facing surface of the medial tibial component. The surface region has a rounded profile or a chamfered profile when viewed in a plane coronally extending from an outer edge of the medial tibial component to the mesial edge of the medial tibial component. The tibial implant includes a second surface region that joins a mesial edge and a tibial-facing surface of the lateral tibial component. The surface region has a rounded profile or a chamfered profile when viewed in a plane coronally extending from an outer edge of the lateral tibial component to the mesial edge of the lateral tibial component. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-cruciate implant configured to replace both medial and lateral compartments of a native tibia. The bi-cruciate implant includes a tibial implant having a medial tibial component and a lateral tibial component. A surface region joins a mesial edge and a tibial-facing surface of the medial tibial component. The surface region has a rounded profile or a chamfered profile when viewed in a plane coronally extending from an outer edge of the medial tibial component to the mesial edge of the medial tibial component. The tibial implant includes a second surface region that joins a mesial edge and a tibial-facing surface of the lateral tibial component. The second surface region has a rounded profile or a chamfered profile when viewed in a plane coronally extending from an outer edge of the lateral tibial component to the mesial edge of the lateral tibial component. 
     In one version of this aspect of the invention, the surface region, when viewed in the plane, has a straight line profile. 
     In one version of this aspect of the invention, the surface region, when viewed in the plane, has a concave curvilinear profile. 
     In another aspect, the invention provides an orthopedic implant includes a tibial implant including one or both of a medial tibial component and a lateral tibial component. At least one of the medial tibial component and the lateral tibial component has a non-straight mesial edge when viewed in a plane transversely extending from an outer edge of the medial tibial component or the lateral tibial component to the mesial edge of the medial tibial component or the lateral tibial component. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant that includes a tibial implant having a medial tibial component. The medial tibial component has a non-straight mesial edge when viewed in a plane transversely extending from an outer edge of the medial tibial component to the mesial edge of the medial tibial component. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant that includes the tibial implant including the lateral tibial component. The lateral tibial component has a non-straight mesial edge when viewed in a plane transversely extending from an outer edge of the lateral tibial component to the mesial edge of the lateral tibial component. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-unicompartmental implant configured to replace both medial and lateral compartments of a native tibia. The bi-unicompartmental implant includes a tibial implant having a medial tibial component and a lateral tibial component. The medial tibial component and the lateral tibial component have the non-straight mesial edge. 
     In one version of this aspect of the invention, the non-straight mesial edge has a concave curvilinear profile. 
     In one version of this aspect of the invention, the non-straight mesial edge has a concave profile includes a plurality of connected straight line segments. 
     In one version of this aspect of the invention, the medial tibial component and the lateral tibial component each comprise a tibial baseplate. 
     In one version of this aspect of the invention, the medial tibial component and the lateral tibial component each comprise a tibial insert. 
     In another aspect, the invention provides an orthopedic implant including a tibial implant having a medial tibial component and a lateral tibial component. The medial tibial component has a distal surface and a proximal surface. The lateral tibial component has a distal surface and a proximal surface. The proximal surface of the medial compartment has a different posterior slope than the proximal surface of the lateral compartment. In one version of this aspect of the invention, the distal surface of the medial tibial component and the distal surface of the lateral tibial component have the same posterior slope. In another version of this aspect of the invention, the distal surface of the medial compartment has a different posterior slope than the distal surface of the lateral compartment. In another version of this aspect of the invention, the tibial implant is a tibial baseplate that includes the medial tibial component and the lateral tibial component. 
     In another aspect, the invention provides an orthopedic implant including a tibial implant having one or both of a medial tibial component and a lateral tibial component. At least one of the medial tibial component and the lateral tibial component includes a distal surface having a convex geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant that includes a tibial implant having a medial tibial component. The medial tibial component and the lateral tibial component include a distal surface having a convex geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a unicompartmental implant that includes a tibial implant having a lateral tibial component. The lateral tibial component includes a distal surface having a convex geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-unicompartmental implant configured to replace both medial and lateral compartments of a native tibia. The bi-unicompartmental implant includes a tibial implant having a medial tibial component and a lateral tibial component. Each of the medial tibial component and the lateral tibial component includes a distal surface having a convex geometry. 
     In one version of this aspect of the invention, the orthopedic implant is a bi-cruciate implant configured to replace both medial and lateral compartments of a native tibia. The bi-cruciate implant includes a tibial implant having a medial tibial component and a lateral tibial component. Each of the medial tibial component and the lateral tibial component includes a distal surface having a convex geometry. 
     In another aspect, the invention provides an orthopedic implant including a tibial implant having a medial tibial component, a lateral tibial component, and an anterior bridge joining the medial tibial component and the lateral tibial component. The anterior bridge is configured such that a superior portion of the anterior bridge drapes over a portion of a tibial eminence. The anterior bridge is configured such that a portion of the anterior-bridge is distal to a distal surface of the medial tibial component and/or a distal surface of the lateral tibial component. In one version of this aspect of the invention, a cavity is formed underneath the anterior bridge. In another version of this aspect of the invention, the tibial implant is configured such that a distal end of the anterior bridge seats in a notch in a tibia when the tibial implant is implanted on the tibia. In another version of this aspect of the invention, the anterior bridge includes a curvilinear outer surface. 
     In another aspect, the invention provides an orthopedic instrument designed to aid in cutting native tibia bone to accommodate a knee implant. The instrument includes a medial cutting guide and a lateral cutting guide. The instrument is configured to allow relative rotation between the medial cutting guide and lateral cutting guide in at least one of a sagittal, coronal or transverse plane. 
     In one version of this aspect of the invention, the medial cutting guide includes a medial transverse cutting slot, and the lateral cutting guide includes a lateral transverse cutting slot. 
     In one version of this aspect of the invention, the medial cutting guide includes a medial tibial eminence cutting slot, and the lateral cutting guide includes a lateral tibial eminence cutting slot. 
     In one version of this aspect of the invention, one of the medial cutting guide and the lateral cutting guide includes a base section that extends away from a lower section. The other of the medial cutting guide and the lateral cutting guide engages the base section and pivots in a transverse plane with respect to the base section. 
     In one version of this aspect of the invention, one of the medial cutting guide and the lateral cutting guide engages the other of the medial cutting guide and the lateral cutting guide and pivots in a sagittal plane with respect to the other of the medial cutting guide and the lateral cutting guide. 
     In one version of this aspect of the invention, one of the medial cutting guide and the lateral cutting guide engages the other of the medial cutting guide and the lateral cutting guide and pivots in a coronal plane with respect to the other of the medial cutting guide and the lateral cutting guide. 
     In one version of this aspect of the invention, there is provided a saw blade dimensioned to slide within the medial transverse cutting slot, the lateral transverse cutting slot, the medial tibial eminence cutting slot, and the lateral tibial eminence cutting slot. 
     In another aspect, the invention provides an orthopedic instrument designed to aid in cutting native tibia bone to accommodate a knee implant. The instrument includes a medial cutting guide, a lateral cutting guide, and a base block. The instrument is configured to allow relative rotation between the block base and at least one of the medial cutting guide and the lateral cutting guide in at least one of a sagittal, coronal or transverse plane. 
     In one version of this aspect of the invention, the instrument is configured to allow relative rotation between the block base and the medial cutting guide in a sagittal plane. 
     In one version of this aspect of the invention, the instrument is configured to allow relative rotation between the block base and the medial cutting guide in a transverse plane. 
     In one version of this aspect of the invention, the instrument is configured to allow relative rotation between the block base and the lateral cutting guide in a sagittal plane. 
     In one version of this aspect of the invention, the instrument is configured to allow relative rotation between the block base and the lateral cutting guide in a transverse plane. 
     In one version of this aspect of the invention, the medial cutting guide includes a medial transverse cutting slot, and the lateral cutting guide includes a lateral transverse cutting slot. 
     In one version of this aspect of the invention, the medial cutting guide includes a medial tibial eminence cutting slot, and the lateral cutting guide includes a lateral tibial eminence cutting slot. 
     In one version of this aspect of the invention, there is provided a saw blade dimensioned to slide within the medial transverse cutting slot, the lateral transverse cutting slot, the medial tibial eminence cutting slot, and the lateral tibial eminence cutting slot. 
     In another aspect, the invention provides an orthopedic instrument designed to aid in cutting native tibia bone to accommodate a knee implant. The instrument includes a medial cutting guide and a lateral cutting guide. The instrument is configured to allow relative translation between the medial cutting guide and the lateral cutting guide in at least one of a mediolateral, anteroposterior or superoinferior direction. 
     In one version of this aspect of the invention, the instrument is configured to allow relative translation between the medial cutting guide and the lateral cutting guide in a mediolateral direction. 
     In one version of this aspect of the invention, the instrument is configured to allow relative translation between the medial cutting guide and the lateral cutting guide in an anteroposterior direction. 
     In one version of this aspect of the invention, the instrument is configured to allow relative translation between the medial cutting guide and the lateral cutting guide in a superoinferior direction. 
     In one version of this aspect of the invention, the medial cutting guide includes a medial transverse cutting slot, and the lateral cutting guide includes a lateral transverse cutting slot. 
     In one version of this aspect of the invention, the medial cutting guide includes a medial tibial eminence cutting slot, and the lateral cutting guide includes a lateral tibial eminence cutting slot. 
     In one version of this aspect of the invention, there is provided a saw blade dimensioned to slide within the medial transverse cutting slot, the lateral transverse cutting slot, the medial tibial eminence cutting slot, and the lateral tibial eminence cutting slot. 
     In another aspect, the invention provides an orthopedic instrument designed to aid in cutting native tibia bone to accommodate a knee implant. The instrument includes a medial cutting guide, a lateral cutting guide, and a base block. The instrument is configured to allow relative translation between the block base and at least one of the medial cutting guide and the lateral cutting guide in at least one of a mediolateral, anteroposterior or superoinferior direction. 
     In one version of this aspect of the invention, the instrument is configured to allow relative translation between the block base and the medial cutting guide in a mediolateral direction. 
     In one version of this aspect of the invention, the instrument is configured to allow relative translation between the block base and the medial cutting guide in an anteroposterior direction. 
     In one version of this aspect of the invention, the instrument is configured to allow relative translation between the block base and the medial cutting guide in a superoinferior direction. 
     In one version of this aspect of the invention, the instrument is configured to allow relative translation between the block base and the lateral cutting guide in a mediolateral direction. 
     In one version of this aspect of the invention, the instrument is configured to allow relative translation between the block base and the lateral cutting guide in an anteroposterior direction. 
     In one version of this aspect of the invention, the instrument is configured to allow relative translation between the block base and the lateral cutting guide in a superoinferior direction. 
     In one version of this aspect of the invention, the medial cutting guide includes a medial transverse cutting slot, and the lateral cutting guide includes a lateral transverse cutting slot. 
     In one version of this aspect of the invention, the medial cutting guide includes a medial tibial eminence cutting slot. The lateral cutting guide includes a lateral tibial eminence cutting slot. 
     In one version of this aspect of the invention, there is provided a saw blade dimensioned to slide within the medial transverse cutting slot, the lateral transverse cutting slot, the medial tibial eminence cutting slot, and the lateral tibial eminence cutting slot. 
     In another aspect, the invention provides an orthopedic instrument designed to aid in cutting native tibia bone to accommodate a knee implant. The instrument includes a cutting guide that is configured to allow varying relative resection depths and/or relative posterior slopes between a medial bone resection and a lateral bone resection. 
     In one version of this aspect of the invention, the cutting guide includes a medial transverse cutting slot and a lateral transverse cutting slot. The medial transverse cutting slot is a first distance from a base wall of the cutting guide. The lateral transverse cutting slot is a second distance from the base wall of the cutting guide. The first distance and the second distance are different. 
     In one version of this aspect of the invention, the cutting guide includes a medial transverse cutting slot and a lateral transverse cutting slot. At least one the medial transverse cutting slot and the lateral transverse cutting slot includes an inlet at a first distance from a first end of a base wall of the cutting guide and an outlet at a second distance from a second end the base wall of the cutting guide. The first distance and the second distance are different. 
     In one version of this aspect of the invention, the cutting guide includes a medial tibial eminence cutting slot and a lateral tibial eminence cutting slot. 
     In another aspect, the invention provides an orthopedic instrument designed to aid in cutting native tibia bone to accommodate a knee implant. The instrument comprises a cutting guide including a first section having an edge and a second section having a transverse cutting slot. The edge is configured to use a cut of one of a medial tibial surface or a lateral tibial surface as a reference to guide resection of the other of the medial tibial surface or the lateral tibial surface. 
     In one version of this aspect of the invention, the second section includes a tibial eminence cutting slot. 
     In one version of this aspect of the invention, the transverse cutting slot includes an inlet at a first distance from a first end of a base wall of the cutting guide and an outlet at a second distance from a second end the base wall of the cutting guide. The first distance and the second distance are different. 
     In another aspect, the invention provides an orthopedic instrument for use with an implant including a medial tibial component and a separate lateral tibial component. The instrument includes a holder configured to temporarily hold the medial tibial component and the lateral tibial component in a desired relative orientation to each other. 
     In one version of this aspect of the invention, the holder includes a handle, a first arm connected to the handle and configured to temporarily hold the medial tibial component, and a second arm connected to the handle and configured to temporarily hold the lateral tibial component. 
     In one version of this aspect of the invention, the first arm is pivotable with respect to the handle such that the medial tibial component can be adjusted in a transverse plane, and the second arm is pivotable with respect to the handle such that the lateral tibial component can be adjusted in the transverse plane. 
     In one version of this aspect of the invention, the first arm is pivotable with respect to the handle such that the medial tibial component can be adjusted in a sagittal plane, and the second arm is pivotable with respect to the handle such that the lateral tibial component can be adjusted in the sagittal plane. 
     These and other features, aspects, and advantages of the present invention will become better understood upon consideration of the following detailed description, drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a perspective view of a unicompartmental implant. 
         FIG. 1B  is a coronal view of a bi-unicompartmental implant. 
         FIG. 1C  is a coronal view of a bi-cruciate retaining implant. 
         FIG. 2A  is a perspective view of a prior art tibial insert, along with sagittal and coronal cross-sections. 
         FIG. 2B  is a perspective view of a tibial insert according to one embodiment of the invention, along with three sagittal cross-sections. 
         FIG. 2C  is a perspective view of a tibial insert according to another embodiment of the invention, along with two sagittal cross-sections. 
         FIG. 2D  is a perspective view of a tibial insert according to another embodiment of the invention, along with three coronal cross-sections. 
         FIG. 3  is a coronal view of a prior art tibial cutting block. 
         FIG. 4A  is a coronal view of cutting guides of a tibial cutting block according to one embodiment of the invention. 
         FIG. 4B  is a sagittal view of the cutting guides of  FIG. 4A . 
         FIG. 4C  is a sagittal view of the cutting guides of  FIG. 4A  with a saw blade and native tibia T. 
         FIG. 4D  is a sagittal view of the cutting guides of  FIG. 4A  with lateral and medial slopes in the resected tibia T. 
         FIG. 5  is a coronal view of cutting guides of a tibial cutting block according to another embodiment of the invention. 
         FIG. 6A  is a perspective view of cutting guides of a tibial cutting block according to another embodiment of the invention. 
         FIG. 6B  is a transverse view of the cutting guides of  FIG. 6A  adjacent a tibia T. 
         FIG. 7A  is a perspective view (bottom) of cutting guides of a tibial cutting block according to another embodiment of the invention, along with an axial view (top) of the cutting guides adjacent a tibia. 
         FIG. 7B  is another perspective view (bottom) and another axial view (top) of the cutting guides of  FIG. 7A . 
         FIG. 8  is a coronal view of cutting guides of a tibial cutting block according to another embodiment of the invention 
         FIG. 9A  is a coronal view of cutting guides of a tibial cutting block according to another embodiment of the invention. 
         FIG. 9B  is a coronal view of cutting guides of a tibial cutting block according to another embodiment of the invention. 
         FIG. 9C  is a coronal view of cutting guides of a tibial cutting block according to another embodiment of the invention. 
         FIG. 9D  is a cross-sectional view taken along line  9 D- 9 D of  FIG. 9A . 
         FIG. 9E  is a cross-sectional view taken along line  9 E- 9 E of  FIG. 9B . 
         FIG. 9F  is a cross-sectional view taken along line  9 F- 9 F of  FIG. 9C . 
         FIG. 10  is a coronal view of cutting guides of a tibial cutting block according to another embodiment of the invention adjacent a tibia T. 
         FIG. 11A  is a transverse view of an instrument according to one embodiment of the invention for holding medial and lateral tibial components in a pre-determined position relative to each other. 
         FIG. 11B  is a transverse view of the instrument of  FIG. 11A  holding medial and lateral tibial components in another pre-determined position relative to each other. 
         FIG. 12A  is a transverse view of an instrument according to another embodiment of the invention for holding medial and lateral tibial components in a pre-determined position relative to each other. 
         FIG. 12B  is a sagittal view of the instrument of  FIG. 12A . 
         FIG. 13A  is a transverse view of an instrument according to another embodiment of the invention for holding medial and lateral tibial components in a pre-determined position relative to each other. 
         FIG. 13B  is a transverse view of the instrument of  FIG. 13A  holding medial and lateral tibial components in another pre-determined position relative to each other. 
         FIG. 14  is a transverse view of an instrument according to one embodiment of the invention for creating holes/slots in medial and lateral tibial compartments. 
         FIG. 15A  is a coronal view of a tibia resected with a rounded edge of the invention compared to a tibia resected with a rectangular edge. 
         FIG. 15B  is a coronal view of a tibia resected with a chamfered edge of the invention compared to a tibia resected with a rectangular edge. 
         FIG. 16  is a transverse view of a prior art tibial component. 
         FIG. 16A  is a sagittal view of the prior art tibial component of  FIG. 16  along line  16 A- 16 A of  FIG. 16 . 
         FIG. 16B  is a sagittal view of a tibial component according to one embodiment of the invention. 
         FIG. 16C  is a sagittal view of a tibial component according to another embodiment of the invention. 
         FIG. 17A  is a transverse view of prior art tibial components on a tibia. 
         FIG. 17B  is a transverse view of tibial components according to one embodiment of the invention. 
         FIG. 17C  is a transverse view of tibial component with an anterior bridge according to one embodiment of the invention. 
         FIG. 17D  is a transverse view of tibial components according to another embodiment of the invention. 
         FIG. 17E  is a transverse view of tibial components according to another embodiment of the invention. 
         FIG. 17F  is a transverse view of tibial components according to another embodiment of the invention. 
         FIG. 18A  shows anterior perspective, posterior perspective, and axial views of a prior art resected tibia. 
         FIG. 18B  shows anterior perspective, posterior perspective, and axial views of a resected tibia according to one embodiment of the invention. 
         FIG. 19A  is a sagittal view of a resected tibia having prior art anterior tibia bone removal, anterior tibia bone removal according to one embodiment of the invention, and anterior tibia bone removal according to another embodiment of the invention. 
         FIG. 19B  is a perspective view of a tibial component according to one embodiment of the invention. 
         FIG. 19C  is a perspective view of a tibial component according to another embodiment of the invention. 
         FIG. 19D  is a perspective view of a tibial component according to another embodiment of the invention. 
         FIG. 19E  is a cross-sectional view of the tibial component of  FIG. 19B  taken along lines  19 E- 19 E of  FIG. 19B . 
         FIG. 19F  is a cross-sectional view of the tibial component of  FIG. 19C  taken along lines  19 F- 19 F of  FIG. 19C . 
         FIG. 20  shows sagittal and transverse views of a tibial component, along with sagittal (A-A) and coronal (B-B) cross-sections of a prior art tibial component (center) and a tibial component according to one embodiment of the invention (right). 
         FIG. 21A  is a sagittal view of a femoral component. 
         FIG. 21B  is a cross-sectional view of a femoral component, taken along line A-A of  FIG. 21A . 
         FIG. 22A  is a cross-sectional view of a femoral component with a modified mesial edge of the lateral condyle according to one embodiment of the invention. 
         FIG. 22B  is a cross-sectional view of a femoral component with a modified mesial edge of the lateral condyle according to another embodiment of the invention. 
         FIG. 22C  is a cross-sectional view of a femoral component with a modified mesial edge of the lateral condyle according to another embodiment of the invention. 
         FIG. 22D  is a cross-sectional view of a femoral component with a modified mesial edge of the lateral condyle according to another embodiment of the invention. 
         FIG. 23A  is a sagittal view of a femoral component with a modified condyle thickness according to one embodiment of the invention. 
         FIG. 23B  is a sagittal view of a femoral component with a modified condyle thickness according to another embodiment of the invention. 
         FIG. 23C  is a sagittal view of a femoral component with a modified condyle thickness according to another embodiment of the invention. 
         FIG. 23D  is a sagittal view of a femoral component with a modified condyle thickness according to another embodiment of the invention. 
         FIG. 23E  is a sagittal view of a femoral component with a modified condyle thickness according to another embodiment of the invention. 
         FIG. 23F  is a sagittal view of a femoral component with a modified condyle thickness according to another embodiment of the invention. 
         FIG. 24  is an anterior perspective view of a femoral component according to one embodiment of the invention. 
         FIG. 24A  is a transverse view of the femoral component of  FIG. 24 , taken along plane A-A of  FIG. 24 . 
         FIG. 24B  is a transverse view of a femoral component according to another embodiment of the invention, taken along plane A-A of  FIG. 24 . 
         FIG. 24C  is a transverse view of a femoral component according to another embodiment of the invention, taken along plane A-A of  FIG. 24 . 
         FIG. 25A  is a sagittal view of a femoral component. 
         FIG. 25B  is a transverse view of a femoral component, along line A-A of  FIG. 25A . 
         FIG. 26A  is a transverse view of a femoral component with a modified mesial edge of the medial condyle according to one embodiment of the invention. 
         FIG. 26B  is a transverse view of a femoral component with a modified mesial edge of the medial condyle according to another embodiment of the invention. 
         FIG. 26C  is a transverse view of a femoral component with a modified mesial edge of the medial condyle according to another embodiment of the invention. 
         FIG. 26D  is a transverse view of a femoral component with a modified mesial edge of the medial condyle according to another embodiment of the invention. 
         FIG. 27A  is a sagittal view of a femoral component. 
         FIG. 27B  is a sagittal view of a femoral component with a modified condyle thickness according to an embodiment of the invention. 
         FIG. 27C  is a sagittal view of a femoral component with a modified condyle thickness according to another embodiment of the invention. 
         FIG. 27D  is a sagittal view of a femoral component with a modified condyle thickness according to another embodiment of the invention. 
         FIG. 27E  is a sagittal view of a femoral component with a modified condyle thickness according to another embodiment of the invention. 
         FIG. 27F  is a sagittal view of a femoral component with a modified condyle thickness according to another embodiment of the invention. 
     
    
    
     Like reference numerals will be used to refer to like or similar parts from Figure to Figure in the following description. 
     DETAILED DESCRIPTION OF INVENTION 
     Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention. Further, while the invention is described in terms of knee implant and knee instrument designs that retain or permit the retention of the anterior cruciate ligament, these designs may also be used for knee implants and instruments that do not retain or do not permit the retention of the anterior cruciate ligament. The definitions of various terms used to describe the present invention are provided below. 
     Definitions 
     The term “native” is used herein to imply natural or naturally occurring in the body. Examples of native structures include musculoskeletal structures such as the tibia bone (or tibia), femoral bone (or femur), tendon, muscle, ligament, etc. 
     The term “implant” is used herein to refer to a prosthetic component designed to augment or replace one or more native structures of the body. For example, a knee implant refers to a prosthetic component designed to augment or replace one or more native structures of the knee. 
     The term “slope” or “posterior slope” is used herein to refer to an angle relative to a tibial long axis measured in a sagittal plane. For example, “slope” or “posterior slope” of a tibial component is the angle between a surface, such as superior or inferior surface, and a tibial mechanical axis projected onto a sagittal plane. 
     The term “long axis” used herein in relation to the tibia bone or a femoral bone and refers to an axis parallel to the length of the bone such as an “anatomical” or “mechanical” axis. The “anatomical” axis refers to a line drawn along the length of the intramedullary canal of the bone. The “mechanical” axis of the femur bone refers to a line joining the center of the femoral head to a point where the “anatomic” axis meets intercondylar notch. The “mechanical” axis of the tibia refers to a line joining the medial tibial spine to the center of the ankle. 
     The term “resection depth” or “depth” refers to distance between native surface of a bone, such as tibia, and a cut surface of the bone generally measured in a superior-inferior direction. 
     The term “tibial eminence” or “tibial spine” is used herein to refer to the native structure of the proximal tibia between the medial and lateral articular surfaces which includes a central prominence and the attachment sites of the anterior cruciate ligament, posterior cruciate ligament, and the menisci. 
     The term “mesial” when used in reference to an implant refers to a portion of an implant situated near or directed towards the median or middle plane of the native bone when the implant is mounted on the native bone. 
     The terms “coronal”/“frontal”, “sagittal” and “transverse”/“axial” planes as used herein refer to anatomical “coronal”/“frontal”, “sagittal” and “transverse”/“axial” planes of the body or the native anatomical structure such as the tibia or femur. The descriptions of form, function or position of an implant or instrument with reference to such planes are intended to represent the form, function or position of the implant or instrument when it is placed/positioned against the anatomical structure in a generally intended manner. 
     Tibial Articular Surface Geometry 
     In contemporary Uni, Bi-Uni, and BCR implants, a sagittal plane cross-section of both the medial and lateral tibial articular surfaces of the tibial insert has a concave geometry composed of a single radius R sag  of about 200 mm, and a coronal plane cross-section has a concave or flat geometry (see  FIG. 2A ). In one embodiment of the invention, the medial or lateral tibial articular surface  216  of the tibial insert  210  has a convex sagittal geometry (i.e., sagittal plane cross-section geometry) composed of a convex radius (R′ sag ,  FIG. 2B ). In another embodiment of the invention, the medial or lateral tibial articular surface  226  of the tibial insert  220  has a sagittal geometry composed of an anterior concave radius (R′ sag1 ), a central convex radius (R′ sag2 ) and a posterior concave radius (R′ sag3 ). In another embodiment of the invention, the medial or lateral tibial articular surface  236  of the tibial insert  230  has a sagittal geometry composed of an anterior concave radius (R′ sag1 ), and a central-posterior convex radius (R′ sag2 ). In preferred embodiments, R′ sag1  has a value of about 60 mm, R′ sag  and R′ sag2  have a value of about 100 mm, and R′ sag3  has a value of about 60 mm. However, these radii (R′ sag , R′ sag1 , R′ sag2 , R′ sag3 ) can range from 10 mm to 300 mm, 30 mm to 200 mm, 50 mm to 100 mm, etc. 
     In another embodiment of the invention, the medial or lateral tibial articular surface  246  of the tibial insert  240  has a concave sagittal geometry (i.e. sagittal plane cross-section geometry) composed of an anterior concave radius (R′ sag4 ) and a different posterior concave radius (R′ sag5 ,  FIG. 2C ). In preferred embodiments, R′ sag4  has a value of about 100 mm, and R′ sag5  has a value of about 130 mm. However, these radii (R′ sag4 , R′ sag5 ,) can range from 10 mm to 300 mm, 30 mm to 200 mm, 50 mm to 100 mm, etc. In other embodiments, the medial or lateral tibial articular surface  256  of the tibial insert  250  can have a generally concave sagittal geometry composed of one of more concave radii and/or flat sections/straight line (see  FIG. 2C ). 
     Further, the coronal geometry (i.e., coronal plane cross-section geometry) of the medial/lateral articular surface  216   a ,  216   b .  216   c  of the tibial insert  210  may be concave ( 216   a ), flat ( 216   b ), or convex ( 216   c ) composed of one or more radii and/or flat sections ( FIG. 2D ). The radii (e.g. R′ cor ) can range from 10 mm to 300 mm, 30 mm to 200 mm, 50 mm to 100 mm, etc. 
     Instrumentation for Accurate Preparation of Tibial Bone 
     During preparation of the tibial bone for a Uni implant, a unicompartmental tibial cutting block  300  is used to resect the bone at the desired resection depth and posterior slope (see  FIG. 3 ). In the prior art tibial cutting block shown in  FIG. 3 , the tibial cutting guide  301  can be adjusted in mediolateral (ML) and superoinferior (SI) direction relative to the block base  302  via the ML adjustment knob  304  and SI adjustment knob  306 . The tibial cutting guide  301  includes a transverse cutting slot  312 . With such a prior art instrumentation, in a Bi-Uni surgical procedure, the unicompartmental tibial cutting block  300  is independently positioned for the medial and lateral compartments to cut the bone in each compartment at the desired resection depth and posterior slope. However, due to manufacturing tolerances of cutting instruments, and inaccuracies in their placement, the desired position of the medial and lateral tibial components relative to each other may not be achieved. For example, if it is desired to achieve 0° posterior slope for the medial component and 4° posterior slope for the lateral component, then with a ±2° variation in tibial slope due to inherent inaccuracies, the actual medial component posterior slope may range from −2° to 2°, and the actual lateral component posterior slope may range from 2° to 6°. Thus, the relative difference in medial and lateral tibial component posterior slopes may range from 0° to 8°, as opposed to desired value of 4°. 
     To address this, in one embodiment of the invention, the tibial cutting block  400  may comprise a medial cutting guide  402  and lateral cutting guide  404 , wherein the medial cutting guide  402  or the lateral cutting guide  404  can pivot/rotate in a plane relative to the other side, such as in a sagittal plane when mounted on the tibia, to allow accurate control of medial/lateral slope relative to the fixed side (see  FIGS. 4A and 4B ). Pivoting can be achieved using a protrusion of the medial cutting guide  402  and/or the lateral cutting guide  404  that is rotatably mounted in a complementary hole in the base section  401  of the medial cutting guide  402 . A saw blade or other such instrument passing through the transverse cutting slots  412 ,  414  and the tibial eminence cutting slots  416 ,  418  can then be used to cut the tibial bone. In the embodiment shown in  FIGS. 4A and 4B , when the medial cutting guide  402  is fixed, the lateral cutting guide  404  can be pivoted as shown to obtain desired posterior slope relative to the medial side. During surgery, a saw blade  431  or other instrument slid through a slot on the fixed side, and resting on the anterior and posterior margins of the tibia, may be used to position the cutting block at the appropriate slope for the fixed side (medial side in  FIG. 4C ). The medial/lateral cutting guide may then be pivoted in a sagittal plane to obtain the desired posterior slope relative to the fixed side. This pivot angle α of the medial/lateral cutting guide relative to the fixed side may range from −10° to 10°, −5° to 5°, −3° to 3° etc. (see  FIG. 4D  where the tibial mechanical axis is labeled A). 
     In another embodiment, the tibial cutting block  500  may comprise a medial cutting guide  502  and a lateral cutting guide  504 , wherein the medial or lateral cutting guide can slide in a plane relative to the fixed side, such as along a superior-inferior direction S-I in a sagittal or coronal plane when mounted on the tibia, to allow desired resection depth relative to the fixed side (see  FIG. 5 ). For example, in the embodiment shown in  FIG. 5 , the medial cutting guide  502  is fixed, and lateral cutting guide  504  can be adjusted to an adjusted position  530  to obtain desired resection depth on the lateral side relative to the medial side. Adjustment can be achieved using a protrusion  532  of the lateral cutting guide  504  that is slidably mounted in a complementary hole  534  in the base  501 . A set screw  536  can secure the lateral cutting guide  504  in the adjusted position  530 . In another embodiment, the lateral cutting guide  504  is fixed and the medial cutting guide  502  can be adjusted to obtain desired resection depth on the lateral side relative to the medial side. A saw blade or other such instrument passing through the transverse cutting slots  512 ,  514  and the tibial eminence cutting slots  516 ,  518  can be used to cut the tibial bone. 
     In another embodiment, the tibial cutting block  600  may comprise a medial cutting guide  602  and a lateral cutting guide  604 , wherein the medial or lateral cutting guide can pivot in a plane relative to the fixed side, such as a transverse plane when mounted on the native tibia T, to allow resection of the tibial eminence along a desired direction relative to the fixed side (see  FIGS. 6A and 6B ). In the embodiment shown in  FIGS. 6A and 6B , the medial cutting guide  602  is fixed, and lateral cutting guide  604  can pivot in a transverse plane. In another embodiment, the lateral cutting guide is fixed and the medial cutting guide can pivot in a transverse plane. Pivoting can be achieved using a protrusion of the cutting guide that is rotatably mounted in a complementary hole in the base as in the tibial cutting block  500 . This pivot angle β of the medial/lateral cutting guide relative to the fixed side may range from −45° to 45°, −30° to 30°, −20° to 20°, −10° to 10° etc. A saw blade or other such instrument passing through the transverse cutting slots  612 ,  614  and the tibial eminence cutting slots  616 ,  618  can be used to cut the tibial bone. The tibial eminence cutting slots  616 ,  618  guide the creation of medial tibial eminence resection  680  and lateral tibial eminence resection  690 . 
     In another embodiment, the tibial cutting block  700  may comprise a medial cutting guide  702  and a lateral cutting guide  704 , wherein the medial cutting guide  702  can pivot and slide in a transverse plane relative to a fixed block base  701 , while the lateral cutting guide can pivot in a transverse and a sagittal plane relative to a fixed block base  701 . See  FIG. 7A  and  FIG. 7B . Pivoting can be achieved using a protrusion of the cutting guide that is rotatably mounted in a complementary hole in the base as in the tibial cutting block  500 . Sliding can be achieved using a channel  788  of the cutting guide that is slidably mounted on a complementary rib  789  in the base  701 . In another embodiment, the tibial cutting block may comprise a medial and a lateral cutting guide, wherein the lateral cutting guide can pivot and slide in a transverse plane relative to a fixed block base, while the medial cutting guide can pivot in a transverse and sagittal plane relative to a fixed block base. This would allow desired relative posterior slope between medial and lateral sides, and relative positions of the medial and lateral tibial eminence wall resections (see  FIG. 7A  and  FIG. 7B ). A saw blade or other such instrument passing through the transverse cutting slots  712 ,  714  and the tibial eminence cutting slots  716 ,  718  can be used to cut the tibial bone. The tibial eminence cutting slots  716 ,  718  guide the creation of medial tibial eminence resection  780 A and lateral tibial eminence resection  790 A ( FIG. 7A ), or the creation of medial tibial eminence resection  780 B and lateral tibial eminence resection  790 B ( FIG. 7B ). 
     In another embodiment shown in  FIG. 8 , the tibial cutting block  800  may comprise a medial cutting guide  802  and a lateral cutting guide  804 . A saw blade or other such instrument passing through the transverse cutting slots  812 ,  814  and the tibial eminence cutting slots  816 ,  818  can be used to cut the tibial bone. The medial cutting guide  802  can pivot as indicated at P in a coronal plane relative to the lateral cutting guide  804  by way of a pivot pin  821  rotatably positioned in a hole  823  of a tab  824  that extends from the lateral cutting guide  804 . The pin  821  is connected to the medial cutting guide  802 . 
     In another embodiment of  FIGS. 9A-9F , a set including tibial cutting blocks  900 A,  900 B,  900 C may be provided with medial and lateral transverse cutting slots having different relative resection depths and/or relative posterior slopes. 
     In  FIGS. 9A and 9D , the tibial cutting block  900 A comprises a medial transverse cutting slot  912 A and a lateral transverse cutting slot  914 A and tibial eminence cutting slots  916 A,  918 A. A saw blade or other such instrument passing through the transverse cutting slots  912 A,  914 A and the tibial eminence cutting slots  916 A,  918 A can be used to cut the tibial bone. The medial transverse cutting slot  912 A and the lateral transverse cutting slot  914 A provide equal resection depth and posterior slope. 
     In  FIGS. 9B and 9E , the tibial cutting block  900 B comprises a medial transverse cutting slot  912 B and a lateral transverse cutting slot  914 B and tibial eminence cutting slots  916 B,  918 B. A saw blade or other such instrument passing through the transverse cutting slots  912 B,  914 B and the tibial eminence cutting slots  916 B,  918 B can be used to cut the tibial bone. The medial transverse cutting slot  912 B and the lateral transverse cutting slot  914 B provide different resection depth and equal posterior slope. 
     In  FIGS. 9C and 9F , the tibial cutting block  900 C comprises a medial transverse cutting slot  912 C and a lateral transverse cutting slot  914 C and tibial eminence cutting slots  916 C,  918 C. A saw blade or other such instrument passing through the transverse cutting slots  912 C,  914 C and the tibial eminence cutting slots  916 C,  918 C can be used to cut the tibial bone. The medial transverse cutting slot  912 C and the lateral transverse cutting slot  914 C provide different resection depth and different posterior slope. 
     In some embodiments of the invention, the medial or lateral tibial bone can be cut first, and then a cutting guide or cutting block configured to use the cut tibial surface as reference may be used to guide the resection of the other side (medial or lateral). For example, in the embodiment shown in  FIG. 10 , the cutting block  1000  includes a lateral cutting guide  1004  having a lateral transverse cutting slot  1014  and a tibial eminence cutting slot  1016 . The cutting block  1000  is configured to align a top edge  1011  of the medial cutting guide  1002  with the cut medial tibial surface as a reference to guide the resection of the lateral tibial compartment using a saw blade or other such instrument passing through the lateral transverse cutting slot  1014  and the tibial eminence cutting slot  1016 . 
     In relation to the above inventions, it is understood that the location of the axis about which a cutting guide pivots/rotates or translates/shifts can differ from those shown in the specific non-limiting embodiments above. 
     Instrumentation for Accurate Placement of Implants 
     In bi-unicompartmental surgery, it may be advantageous to maintain the desired relative positions of the medial and lateral tibial components during the surgical procedure. Therefore, in one embodiment of the invention, an instrument handle is provided to temporarily hold the medial and lateral tibial components in the desired relative positions, such as during cementing and/or seating of the components into the bone, to prevent or minimize relative shift in component positions from their desired or planned positions. The instrument handle can be detached from the medial and lateral tibial components prior to end of the surgical procedure. In another embodiment, an instrument handle is provided to temporarily hold the medial and lateral tibial trial components in the desired relative positions, such as for marking location of tibial implant fixation pegs or location of tibial eminence resections. This would aid in minimizing or preventing relative shift in final implant component positions from the desired or planned locations. 
     In one embodiment, the instrument handle  1110  is a single-piece component that is fabricated to hold the medial tibial component (implant or trial)  1114  and the lateral tibial component (implant or trial)  1112  (e.g., via clamping) in pre-determined positions relative to each other (see  FIGS. 11A and 11B ). This pre-determined position may also be unique for each patient and derived from pre-operative planning for that patient based on computed tomography, magnetic resonance, X-ray or other imaging techniques used to analyze the patient&#39;s native anatomy. 
     In other embodiments, an instrument handle  1210  can be configured during surgery, such as via aid of adjustable arms  1222 , 1224 , to achieve desired orientation of the medial tibial component (implant or trial)  1214  and the lateral tibial component (implant or trial)  1212  in 3D space (see  FIGS. 12A and 12B ). Such rotational or translational adjustments within the instrument handle  1210  may be provided in one or more planes such as sagittal, transverse, or coronal planes. In the non-limiting example embodiment shown in  FIG. 12A , the instrument handle  1210  allows relative orientation of the medial tibial component  1214  and the lateral tibial component  1212  to be adjusted in the transverse plane via pivot pins  1223 , 1225  of each of the adjustable arms  1222 , 1224 . In the non-limiting example embodiment of  FIG. 12B  (lateral view), the instrument handle allows relative orientation of the medial and lateral tibial components to be adjusted in two perpendicular planes via a pivot pin of each of the adjustable arms  1222 , 1224  and a pivot pin of each of the adjustable arms  1232 , 1234 . 
     In another embodiment of the invention, a clip  1310  is provided to temporarily hold (e.g., via clamping) the medial tibial component (implant or trial)  1314  and the lateral tibial component (implant or trial)  1312  in pre-determined relative positions (see  FIGS. 13A and 13B ). 
     In another embodiment, a single-piece tibial trial component  1410  with a handle  1412  and trial tibial baseplate  1414  is provided, wherein the medial compartment  1415  and the lateral compartment  1416  are configured according to the desired location of the medial and lateral tibial implant components. The single-piece tibial trial may include features (tibial fixation peg guide holes  1417 ) to guide the creation of holes/slots in the tibial bone to receive fixation features such as fixation pegs or keels of the tibial implant component (see  FIG. 14 ). The aforementioned single-piece instrument handles, clips, and tibial trial may be made specifically for individual patients according to desired relative orientation/position of the medial and lateral tibial components. The aforementioned single-piece instrument handles, clips, and tibial trial may attach to the tibial components at any location on the component, such as at an anterior location as shown in  FIGS. 11-13 , a central location, or a posterior location, etc. 
     Tibial Component Design 
     In conventional unicompartmental, bi-unicompartmental or bi-cruciate retaining surgical procedure, the medial/lateral surface of the native tibial eminence is resected perpendicular to the transverse tibial bone cuts to match the rectangular coronal geometry of conventional tibial components (see  FIGS. 15A and 15B ). Note the lateral transverse bone cut  1521  and medial transverse bone cut  1522  in  FIG. 15A . The rectangular coronal geometry of conventional tibial components can cause an increase in stress within the tibial bone near the intersections I 1  and I 2  of the tibial eminence bone cuts  1531 , 1532  and the transverse tibial bone cuts  1521 , 1522  respectively, and potentially lead to fracture of the tibial bone. To address this, in one embodiment of the invention, a mesial edge (inner edge or edge closer to the tibial eminence) of the tibial component  1500 A (tibial baseplate and/or insert) has a rounded coronal geometry (see  15 R in  FIG. 15A ). The rounded edge  15 R may have a radius r, ranging from 2 to 50 mm, 10 to 40 mm, 15 to 25 mm etc. In another embodiment, a mesial edge of the tibial component  1500 B or tibial baseplate has a chamfered coronal geometry (see  15 C in  FIG. 15B ). The chamfered edge  15 C may have a chamfer angle γ, ranging from 2° to 75°, 15° to 50°, 25° to 40° etc. Corresponding to these embodiments, the tibial eminence bone may be prepared to have a rounded or chamfered coronal geometry at the intersection of the tibial eminence and transverse plane cuts. With these embodiments of the invention, a portion of compressive load acting on the tibial component  1500 A or  1500 B is transferred to bone at the intersections I 1 , I 2  of the tibial eminence cut and transverse bone cut which may reduce risk of bone fracture. 
     In a conventional BCR tibial component  1600 A (tibial baseplate and/or tibial insert) shown in  FIGS. 16 and 16A  having an anterior bridge  1635 , the proximal surface  1621  of the lateral side  1620  and the proximal surface  1631  of the medial side  1630  lie on the same plane, and the distal surfaces  1622 ,  1632  of the medial and lateral sides  1620 , 1630  lie on the same plane, i.e., the distal and proximal surfaces of the medial and lateral sides have the same posterior slope (see  FIG. 16A ). In contrast, in the native knee, the medial and lateral compartments have different slopes even in the same individual subject/patient. To accommodate this variation in the native anatomy, in one embodiment of the invention, the tibial component  1600 B, shown in  FIG. 16B , has an anterior bridge similar to  1635  of  FIG. 16 , and is designed such that the distal surface  1652  and the proximal surface  1651  of the medial side  1650  have a different posterior slope than the distal surface  1642  and proximal surface  1641  of the lateral side  1640 . The difference in slopes (δ) can be about 5°, but can range from −15° to 15°, −10° to 10°, −5° to 5°, −2° to 2° etc. (see  FIG. 16B ). In another embodiment, the tibial component  1600 C, shown in  FIG. 16C , has an anterior bridge similar to  1635  of  FIG. 16 , and is designed such that the distal surface  1672  of the medial side  1670  and the distal surface  1662  of the lateral side  1660  have the same posterior slope, but the proximal surface  1671  of the medial side  1670  and the proximal surface  1661  and the lateral side  1660  have different posterior slopes (see  FIG. 16C ). The difference in slopes  1677  can be about 5°, but can range from −15° to 15°, −10° to 10°, −5° to 5°, −2° to 2° etc. Such implants may be manufactured from additive manufacturing processes such as laser sintering, 3D printing etc. These implants  1600 B,  1600 C may also be designed specifically for individual patients according to their native anatomies. 
     In a transverse plane, the conventional Uni, Bi-Uni and BCR lateral tibial component  1710  and medial tibial component  1712  have a straight mesial edges  1711 ,  1713  respectively (see  FIG. 17A ). Generally, when these tibial components  1710 ,  1712  are implanted in the knee, this straight mesial edges  1711 , 1713  of the tibial implant are parallel to the anteroposterior axis AP of the tibia. In contrast to this geometry of the conventional implants, the mesial boundary of the native tibial eminence in the transverse plane is not a straight line. Therefore, preparation of the tibial eminence to accommodate the straight edge of the conventional implant may result in excess removal of tibial eminence bone, which could increase the risk of tibial eminence bone fracture. To address this, in one embodiment of the invention, the mesial edge  1721  of the lateral tibial component  1720  and the mesial edge  1723  of the medial tibial component  1722  have an arcuate geometry in the transverse plane (see  FIG. 17B ). In another embodiment of the invention, the mesial edge  1731  of the lateral tibial component  1730  and the mesial edge  1733  of medial tibial component  1732  have an arcuate geometry in the transverse plane (see  FIG. 17C ). The lateral tibial component  1730  and the medial tibial component  1732  are attached via anterior bridge  1735 . In mesial edges  1721 ,  1723 ,  1731 ,  1733 , this arcuate geometry can extend over the entire mesial edge or a portion thereof. 
     In other embodiments, the arcuate geometry may be approximated with three straight lines  1741 ,  1742 ,  1743  for the lateral tibial component  1740  and three straight lines  1745 ,  1746 ,  1747  for the medial tibial component  1744  (see  FIG. 17D ). 
     In other embodiments, in a transverse plane, the mesial edge  1751  for the lateral tibial component  1750  and the mesial edge  1753  for the medial tibial component  1754  may include one or more convex/concave arcs, or multiple line segments (see  FIG. 17E ). 
     In other embodiments, the mesial edge  1761  for the lateral tibial component  1760  and the mesial edge  1763  for the medial tibial component  1764  may include a rectangular notch/cutout extending over a portion of the mesial edge (see  FIG. 17F ). 
     In conventional bi-unicompartmental knee surgery using a lateral tibial component  1810  and a medial tibial component  1812 , the medial and/or lateral tibial bone is resected with a transverse cut going across/through the anteroposterior extent of the medial/lateral tibial compartment, and the tibial eminence is resected with a sagittal cut going across/through the anteroposterior extent of the tibial eminence (see  FIG. 18A ). This creates mediolateral widths of the tibial bone retained between the medial plateau  1822  and lateral plateau  1821  of w ant , w cen  and w pos  (see the transverse view at the bottom of  FIG. 18A ). These bony resections may weaken the tibial eminence and pose the risk of fracture near the anterior margin of the eminence due to the load acting on the eminence from the anterior cruciate ligament. To address this, in one embodiment of the invention, the surgical preparation of the bone and implant design are configured to increase the amount of retained anterior tibial bone. This may be achieved, for example, by resecting the tibial eminence along multiple planes rather than a single plane and limiting the anteroposterior extent of the transverse medial and/or lateral tibial cut to preserve greater amount of the anterior tibial bone (see  FIG. 18B ). With this surgical technique and implant design, in the transverse plane, the mediolateral width of the tibial bone retained between the medial and lateral plateaus would be wider anteriorly than centrally or posteriorly (w′ ant &gt;w′ cen  and/or w′ ant &gt;w′ pos ). In the embodiment of  FIG. 18B , a lateral tibial component  1830  includes a mesial edge  1831  that joins a chamfered anterior edge  1832  that extends to an anterior point  1834  intermediate the mesial edge  1831  and the lateral edge  1835 . A medial tibial component  1840  includes a mesial edge  1841  that joins a chamfered anterior edge  1842  that extends to an anterior point  1844  intermediate the mesial edge  1841  and the medial edge  1845 . 
     Looking at  FIG. 16A , in a conventional BCR implant, the distal surface  1636  of the anterior-bridge  1635  is in the same plane as the distal surfaces  1622 ,  1632  of the medial and lateral side compartments  1620 , 1630 . Consequently, tibial bone in the anterior portion of the tibial eminence has to be removed to accommodate the anterior-bridge of the tibial component. See  FIG. 19A . The anteroposterior width of the tibial bone resection to accommodate the anterior-bridge is about 10 millimeters as shown in  FIG. 19A . However, this removal of bone can reduce the strength of the eminence bone leading to risk of bone fracture. To address this, in one tibial component  1910  shown in  FIGS. 19B, 19D, and 19E  and another tibial component  1950  shown in  FIGS. 19C and 19F , the anterior-bridge is configured such that a superior portion of the anterior-bridge drapes over the bone anterior to the tibial eminence, thereby creating a dome or cavity underneath the anterior bridge. 
     Referring to  FIGS. 19B, 19D, and 19E , the tibial component  1910  includes a lateral tibial component  1930  and a medial tibial component  1920  connected by an anterior bridge  1935 . The lateral tibial component  1930  has a proximal surface  1932  and a distal surface  1934 . A superior portion of the anterior bridge  1935  drapes over the tibia bone anterior to the tibial eminence, thereby creating a cavity  1937  underneath the anterior bridge  1935 . 
     Referring now to  FIGS. 19C and 19F , the tibial component  1950  includes a lateral tibial component  1970  and a medial tibial component  1960  connected by an anterior bridge  1975 . The lateral tibial component  1970  has a proximal surface  1972  and a distal surface  1974 . A superior portion of the anterior bridge  1975  drapes over the tibia bone anterior to the tibial eminence, thereby creating a cavity  1977  underneath the anterior bridge  1975 . Further, to achieve sufficient strength against failure of the anterior bridge  1975 , a portion of the anterior bridge  1975  also extends below the level of the distal surface of the medial component  1960  and/or the lateral tibial component  1970 . In the tibial component  1950 , the distal portion  1978  of the anterior bridge  1975  is not in the same plane as the distal surfaces of the medial and lateral tibial components  1960 , 1970 . Thus, in some embodiments of the present invention, the distal portion of the anterior bridge may not be in the same plane as the distal surfaces of the medial and lateral tibial components. 
     In conventional knee implants, the distal surface  2012  of the tibial component  2010  interfacing with the tibial bone has a flat/planar geometry, and the corresponding tibial bone cut is also planar (see  FIG. 20 ). In one embodiment of the invention, a tibial component  2020  includes a distal surface  2022  (facing the tibial bone) having a convex geometry in the coronal plane A-A and the sagittal plane B-B (see  FIG. 20 ). This convex geometry of the tibial component  2020  may interface with a concavity prepared in the tibial bone to better resist loosening caused by eccentric loading acting on the tibial component  2020 . In another embodiment of the invention, the distal surface of the tibial component may have a concave geometry facing the tibial bone. 
     Femoral Component Design: 
     The insertion of the native ACL on the femoral side lies along the mesial side of the lateral condyle  2110  of the femoral component (see  FIG. 21A ). The ACL insertion in the average knee has a width wACL of about 11 mm, and a height hACL of about 20 mm. The posterior edge of the ACL insertion is approximately 6.5 mm from posterior femoral condyle cartilage surface, and approximately 14 mm from distal femoral condyle cartilage surface (see  FIGS. 21A and 21B ). In a conventional femoral component, the condyle thickness of the implant is greater than or equal to about 8 mm. Thus, removal of corresponding bone from the posterior condyle of the femur to accommodate the femoral implant can result in removal of significant proportion of the ACL insertions and/or ACL fibers at/near the insertion, thereby weakening the ligament. 
     To address this, in one set of embodiments, the geometry of the femoral component is modified to remove material along a mesial edge of the lateral condyle of the femoral component. In  FIG. 22A , there is comparison of a conventional lateral condyle  2110  and a lateral condyle  2120  of the present invention in which a removal of material can be achieved through a gradual chamfer surface region  2122  at the mesial edge  2121 . In  FIG. 22B , there is comparison of a conventional lateral condyle  2110  and a lateral condyle  2130  of the present invention in which a removal of material can be achieved with a smooth convex arcuate profile surface region  2132  at the mesial edge  2131 . In  FIG. 22C , there is comparison of a conventional lateral condyle  2110  and a lateral condyle  2140  of the present invention in which a removal of material can be achieved a sharp concave curvilinear transition surface region  2142  in condyle thickness near the mesial edge  2141 . In  FIG. 22D , there is comparison of a conventional lateral condyle  2110  and a lateral condyle  2150  of the present invention in which a removal of material can be achieved a sharp concave transition surface region  2152  in condyle thickness near the mesial edge  2151 . In preferred embodiments, the parameters w a  and h a  (shown in  FIG. 22C ) have a value of about 3 mm, but can range from 0.5 to 6 mm, 1 to 4 mm etc. The parameter w a  can be measured perpendicularly from the mesial edge  2141  to a normal line N 1  to a junction of the surface region and the inner surface  2143 . The parameter h a  can be measured perpendicularly from the inner surface  2143  to a normal line N 2  to a junction of the surface region and the mesial edge, is in a range of range 0.5 to 7 millimeters. 
     In a conventional femoral component, the posterior and distal condyle thickness (t pc  and t dc ) are generally equal and about 8 mm or greater (range 8 to 12 mm). In some embodiments of the invention, the thickness of the posterior femoral condyle may be reduced, resulting in modification of the sagittal plane geometry of the inner surface of the femoral implant interfacing with the femoral bone. In some embodiments (see  FIGS. 23A-23F ), the posterior (t′pc) and/or posterodistal condyle thickness (t′pdc) may be reduced to about 6.5 mm (range 1 mm to 7.5 mm), while the distal condyle thickness (t′dc) is greater and about 8 mm (range 8 mm to 15 mm). In other embodiments, the posterior (t′pc), posterodistal (t′pdc), and distal condyle thickness (t′dc) may be equal and about 6.5 mm (range 1 mm to 7.5 mm). In the above embodiments, the sagittal geometry of the inner surface of the posterior, posterodistal and distal condyle interfacing with the femoral bone may comprise one or more straight lines as in embodiments of  FIGS. 23A-23E , or may be arcuate as in embodiment of  FIG. 23F . 
     Specifically, in  FIG. 23A , there is a comparison of a conventional lateral condyle  2310  (having posterior condyle  2312 , posterodistal condyle  2314  and distal condyle  2316 ) and a lateral condyle of the present invention in which an inner surface  2321  (shown in dashed lines) creates reduced posterior condyle thickness (t′pc) and reduced posterodistal condyle thickness (t′pdc). In  FIG. 23B , there is a comparison of a conventional lateral condyle  2310  and a lateral condyle of the present invention in which an inner surface  2341  (shown in dashed lines) creates reduced posterior condyle thickness (t′pc). In  FIG. 23C , there is a comparison of a conventional lateral condyle  2310  and a lateral condyle of the present invention in which an inner surface  2351  (shown in dashed lines) creates reduced posterior condyle thickness (t′pc) and reduced posterodistal condyle thickness (t′pdc). In  FIG. 23D , there is a comparison of a conventional lateral condyle  2310  and a lateral condyle of the present invention in which an inner surface  2361  (shown in dashed lines) creates reduced posterior condyle thickness (t′pc) and reduced posterodistal condyle thickness (t′pdc). In  FIG. 23E , there is a comparison of a conventional lateral condyle  2310  and a lateral condyle of the present invention in which an inner surface  2371  (shown in dashed lines) creates reduced posterior condyle thickness (t′pc) and reduced posterodistal condyle thickness (t′pdc). In  FIG. 23F , there is a comparison of a conventional lateral condyle  2310  and a lateral condyle of the present invention in which an inner surface  2381  (shown in dashed lines) creates reduced posterior condyle thickness (t′pc) and reduced posterodistal condyle thickness (t′pdc). 
     Reduction in thickness of the femoral condyles may reduce strength of the condyle. To address this, in further embodiments of the invention, reinforcing structures such as rectangular fins or semi-cylindrical fins, may be added to the inner surface of one or both of the femoral condyles interfacing with the femoral bone (see  FIGS. 24-24C ). In  FIGS. 24 and 24A , an example femoral component  2410  of the present invention includes a lateral condyle  2412  and a medial condyle  2414  including a rectangular fin  2416  that extends away from the inner surface of the medial condyle  2414 . In  FIG. 24A , there is a comparison of a conventional lateral condyle having straight inner surface  2400  (in dashed lines) of the femoral condyle and a femoral component  2410  of the present invention having a medial condyle  2414  including a central rectangular fin  2416 . In  FIG. 24B , there is a comparison of a conventional lateral condyle having straight inner surface  2400  (in dashed lines) of the femoral condyle and a femoral component  2420  of the present invention having a medial condyle  2424  including a pair of spaced apart rectangular fins  2426 . In  FIG. 24C , there is a comparison of a conventional lateral condyle having straight inner surface  2400  (in dashed lines) of the femoral condyle and a femoral component  2430  of the present invention having a medial condyle  2434  including a central semi-cylindrical fin  2436 . 
     The insertion of the native PCL on the femoral side lies along the mesial side of the medial femoral condyle  2514  (see  FIGS. 25A and 25B ). The PCL insertion in the average knee has a width wPCL of about 26 mm, a height hACL of about 16 mm. The posterior edge of the PCL insertion is approximately 7 mm from posterior femoral condyle bone surface, approximately 7 mm from distal femoral condyle bone surface, and approximately 5 mm from posterodistal femoral condyle bone surface (see  FIGS. 25A and 25B ). In a conventional femoral component, the condyle thickness of the implant is greater than or equal to about 8 mm. Thus, removal of corresponding bone from the posterior condyle of the femur to accommodate the femoral implant can result in removal of significant proportion of the PCL insertions and PCL fibers at/near the insertion, thereby weakening the ligament. 
     To address this, in one set of embodiments, the geometry of the femoral component is modified to remove material along a mesial edge of the medial condyle (see  FIGS. 26A-26D ). In  FIG. 26A , there is comparison of a conventional medial condyle  2610  and a medial condyle  2620  of the present invention in which a removal of material can be achieved through a gradual chamfer surface region  2622  at the mesial edge  2621 . In  FIG. 26B , there is comparison of a conventional medial condyle  2610  and a medial condyle  2630  of the present invention in which a removal of material can be achieved through a smooth concave curvilinear arcuate profile surface region  2632  at the mesial edge  2631 . In  FIG. 26C , there is comparison of a conventional medial condyle  2610  and a medial condyle  2640  of the present invention in which a removal of material can be achieved through a sharp concave transition surface region  2642  at the mesial edge  2641 . In  FIG. 26D , there is comparison of a conventional medial condyle  2610  and a medial condyle  2650  of the present invention in which a removal of material can be achieved through a sharp convex transition surface region  2652  at the mesial edge  2651 . In preferred embodiments, the parameters w p  and h p  have a value of about 4 mm, but can range from 0.5 to 7 mm, 2 to 4 mm, etc. The parameters w p  and h p  can be measured using the methodology described above for measuring parameters w a  and h a . 
     In a conventional femoral component, the posterior, distal and posterodistal condyle thickness (t p , t dc  and t pdc ) are generally equal and about 8 mm or greater (range 8 to 12 mm). In some embodiments of the invention, the thickness of the femoral condyle may be reduced, resulting in modification of the sagittal plane geometry of the inner surface of the femoral implant interfacing with the femoral bone. In some embodiments ( FIGS. 27B-27F ), the posterodistal condyle thickness (t′pdc) may be reduced to about 5 mm (range 1 mm to 7.5 mm), while the posterior (t′pc) and distal condyle thickness (t′dc) are greater and about 8 mm (range 8 mm to 15 mm). In other embodiments the posterodistal condyle thickness (t′ pdc ) may be about 5 mm (range 1 mm to 7.5 mm), the distal condyle thickness (t′ dc ) may be about 6.5 mm (range 1 mm to 7.5 mm), and the posterior condyle thickness (t′ pc ) may be about 8 mm or greater. In other embodiments, the posterodistal condyle thickness (t′ pdc ) may be about 5 mm (range 1 mm to 7.5 mm), while the posterior and distal condyle thickness (t′ pc , t′ dc ) may be about 6.5 mm (range 1 mm to 7.5 mm). In the above embodiments, the sagittal geometry of the inner surface of the posterior, posterodistal and distal condyle interfacing with the femoral bone may be composed of one of more straight lines as in embodiments of  FIGS. 27A-27E , or may be arcuate as in embodiment of  FIG. 27F . 
     Specifically,  FIG. 27A  shows a conventional medial condyle  2710  including a posterior condyle  2712 , a posterodistal condyle  2714  and a distal condyle  2716  having a posterior condyle thickness (t pc ), a posterodistal condyle thickness (t pdc ), and distal condyle thickness (t dc ), respectively. In  FIG. 27B , there is a comparison of the conventional medial condyle  2710  and a medial condyle of the present invention in which an inner surface  2721  (shown in dashed lines) creates reduced posterodistal condyle thickness (t′pdc). In  FIG. 27C , there is a comparison of the conventional medial condyle  2710  and a medial condyle of the present invention in which an inner surface  2731  (shown in dashed lines) creates reduced posterodistal condyle thickness (t′pdc) and reduced distal condyle thickness (t′ dc ). In  FIG. 27D , there is a comparison of the conventional medial condyle  2710  and a medial condyle of the present invention in which an inner surface  2741  (shown in dashed lines) creates reduced posterior condyle thickness (t′ pc ) and reduced posterodistal condyle thickness (t′ pdc ) and reduced distal condyle thickness (t′ dc ). In  FIG. 27E , there is a comparison of the conventional medial condyle  2710  and a medial condyle of the present invention in which an inner surface  2751  (shown in dashed lines) creates reduced posterior condyle thickness (t′ pc ) and reduced posterodistal condyle thickness (t′ pdc ) and reduced distal condyle thickness (t′ dc ). In  FIG. 27F , there is a comparison of the conventional medial condyle  2710  and a medial condyle of the present invention in which an inner surface  2761  (shown in dashed lines) creates reduced posterodistal condyle thickness (t′ pdc ) and reduced distal condyle thickness (t′ dc ). 
     Reduction in thickness of the femoral medial condyles may reduce strength of the condyle. To address this, in further embodiments of the invention, the reinforcing structures such as rectangular or cylindrical fins may be added to the inner surface of the femoral medial condyles interfacing with the femoral bone as in the embodiments of the invention shown in  FIGS. 24-24C . 
     Prosthesis Materials and Construction: 
     The prosthetic components can be constructed in various sizes to fit a range of typical patients, or the components can be custom-designed for a specific patient based on data provided by a surgeon, e.g., after physical and radiography examination of the specific patient. The implants described herein can be constructed in various manners and can be made from one or more materials. Implant components (e.g., tibial insert, tibial baseplate, femoral component, tibial cutting block, instrument handle) can be machined, cast, forged, molded, or otherwise constructed out of a medical grade, physiologically acceptable material such as a cobalt chromium alloy, a titanium alloy, stainless steel, ceramic, etc. Other examples of materials for the implants include polyolefins, polyethylene, ultra-high molecular weight polyethylene, medium-density polyethylene, high-density polyethylene, medium-density polyethylene, highly cross-linked ultra-high molecular weight polyethylene (UHMWPE), etc. Exemplary embodiments of UHMWPE prosthesis materials and manufacturing processes are described in U.S. Pat. No. 5,879,400 filed Feb. 13, 1996 entitled “Melt-Irradiated Ultra High Molecular Weight Polyethylene Prosthetic Devices”; U.S. Patent Application Publication No. 2009/0105364 filed Dec. 12, 2008, entitled “Radiation And Melt Treated Ultra High Molecular Weight Polyethylene Prosthetic Devices”; U.S. Pat. No. 7,906,064 filed Nov. 29, 2006 entitled “Methods For Making Oxidation Resistant Polymeric Material”; U.S. Pat. No. 8,293,811 filed Apr. 5, 2010 entitled “Methods For Making Oxidation-Resistant Cross-Linked Polymeric Materials”; U.S. Pat. No. 7,166,650 filed Jan. 7, 2005 entitled “High Modulus Crosslinked Polyethylene With Reduced Residual Free Radical Concentration Prepared Below The Melt”; and U.S. Patent Application Publication No. 2008/0215142 filed Mar. 3, 2008 entitled “Cross-Linking Of Antioxidant-Containing Polymers”, which are hereby incorporated by reference in their entireties. 
     The devices disclosed herein can be designed to be disposed of after a single use, or they can be designed to be used multiple times. In either case, the device can be reconditioned for reuse after at least one use. Reconditioning can include any combination of the steps of disassembly of the device, followed by cleaning or replacement of particular pieces, and subsequent reassembly. In particular, the device can be disassembled, and any number of the particular pieces or parts of the device can be selectively replaced or removed in any combination. Upon cleaning and/or replacement of particular parts, the device can be reassembled for subsequent use either at a reconditioning facility, or by a surgical team immediately prior to or during a surgical procedure. Those skilled in the art will appreciate that reconditioning of a device can utilize a variety of techniques for disassembly, cleaning/replacement, and reassembly. Use of such techniques, and the resulting reconditioned device, are all within the scope of the present application. 
     One skilled in the art will appreciate further features and advantages of the invention based on the above-described non-limiting embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. 
     All publications and references cited herein are expressly incorporated herein by reference in their entirety.