Abstract:
A posterior cruciate ligament retaining knee implant prosthesis comprising a femoral component including a medial condyle and a lateral condyle separated from one another by an intercondylar channel adapted to accommodate throughput of a native cruciate ligament, both the medial condyle and the lateral condyle posteriorly terminate individually, the medial condyle including a medial condyle bearing surface and the lateral condyle including a lateral condyle bearing surface, the femoral component including an anterior cam, and a tibial component including a medial condyle receiver having a medial condyle receiver bearing surface, the tibial component also including a lateral condyle receiver having a lateral condyle receiver bearing surface, the tibial component also including an anterior post.

Description:
RELATED ART 
     Field of the Invention 
       [0001]    The present disclosure relates to orthopedic knee prosthetics and, more specifically, to anterior stabilized orthopedic knee prosthetics for use with posterior cruciate retaining total knee arthroplasty procedures. 
       BACKGROUND 
       [0002]    The knee is the largest joint in the body. Normal knee function is required to perform most everyday activities. The knee is made up of the lower end of the femur, which rotates on the upper end of the tibia, and the patella, which slides in a groove on the end of the femur. Large ligaments attach to the femur and tibia to provide stability. The long thigh muscles give the knee strength. 
         [0003]    The joint surfaces where these three bones touch are covered with articular cartilage, a smooth substance that cushions the bones and enables them to move easily. The condition of this cartilage lining the knee joint is a key aspect of normal knee function and is important to the physician when evaluating a potential need for a knee joint replacement. 
         [0004]    All remaining surfaces of the knee are covered by a thin, smooth tissue liner called the synovial membrane. This membrane releases a special fluid that lubricates the knee, reducing friction to nearly zero in a healthy knee. 
         [0005]    Normally, all of these components work in harmony. But disease or injury can disrupt this harmony, resulting in pain, muscle weakness, and reduced function. 
         [0006]    In addition to the smooth cartilage lining on the joint surfaces, there are two smooth discs of cartilage that cushion the space between the bone ends. The inner disc is called the medial meniscus, while the disc on the outer side of the knee joint is called the lateral meniscus. The role of the menisci is to increase the conformity of the joint between the femur and the tibia. The menisci also play an important function as joint shock absorbers by distributing weight-bearing forces, and in reducing friction between the joint segments. 
         [0007]    There are also four major ligaments that play an important part in stability of the knee joint. The Medial Collateral Ligament (MCL) and the Lateral Collateral Ligament (LCL) are located on opposing sides on the outside of the joint. The Anterior Cruciate Ligament (ACL) and the Posterior Cruciate Ligament (PCL) are more centrally located ligaments within the joint. The ACL attaches to the knee end of the Femur, at the back of the joint and passes down through the knee joint to the front of the flat upper surface of the Tibia. It passes across the knee joint in a diagonal direction and with the PCL passing in the opposite direction, forms a cross shape, hence the name cruciate ligaments. 
         [0008]    Total knee replacement (TKR), also referred to as total knee arthroplasty (TKA), is a surgical procedure where worm, diseased, or damaged surfaces of a knee joint are removed and replaced with artificial surfaces. Materials used for resurfacing of the joint are not only strong and durable but also optimal for joint function as they produce as little friction as possible. 
         [0009]    The “artificial joint or prosthesis” generally has three components: (1) a distal femoral component usually made of a biocompatible material such as metal alloys of cobalt-chrome or titanium; (2) a proximal tibial component also made of cobalt chrome or titanium alloy; and a bearing component disposed there between usually formed of a plastic material like polyethylene. 
         [0010]    In total knee arthroplasty (TKA) there are three main types of implants: The first main type is the posterior cruciate retaining (PCR) total knee arthroplasty, where the surgeon retains the posterior cruciate ligament and sacrifices the anterior cruciate ligament. The second main type is the posterior stabilizing (PS) total knee arthroplasty, where the surgeon sacrifices both the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). With a PS TKA posterior stabilization is introduced into the TKA by using a cam/post mechanism. The third main type is the posterior cruciate sacrificing (PCS) TKA where the surgeon sacrifices both the ACL and the PCL, but does not use a cam/post mechanism for posterior stabilization. Rather, this TKA type uses constraint in the polyethylene to stabilize the anteroposterior movement. 
         [0011]    Any of the above three main types of TKA implant can have a fixed bearing (FB) design or a mobile bearing (MB) design. With the fixed bearing design, the polyethylene insert is either compression molded or fixed in the tibial tray using a locking mechanism. In a mobile bearing design, the polyethylene insert is free to either rotate, translate or both rotate and translate. 
         [0012]    While knee arthroplasty is known as one of the most consistently successful surgeries offered, there is room for improvement. For example, the ACL is sacrificed during the installation of a total knee arthroplasty system, and doing so can have a negative clinical impact for some patients. 
         [0013]    The role of the ACL is to pull the femur in the anterior direction at terminal extension and at full extension. The ACL, attached to the lateral condyle of the femur also works as a tether and keeps the lateral condyle in contact with the lateral meniscus. The PCL pulls the femur in the posterior direction with increasing flexion. The PCL also acts as a tether on the medical condyle of the femur, keeping the medial condyle in contact with the medial meniscus. Together these two ligaments are vitally important to the stability of the knee joint, especially in contact sports and those that involve fast changes in direction and twisting and pivoting movements. Therefore a torn or absent ACL has serious implications for the stability and function for the knee joint. In other orthopedic fields, surgeons usually recommend ACL replacement surgery for a torn ACL because without the ACL, the femorotibial joint becomes unstable. It is assumed that this instability leads to meniscus and cartilage damage. Unfortunately, the ACL is sacrificed in TKA. 
         [0014]    Known TKA implants provide for posterior stabilization, but not anterior stabilization. What is needed, therefore, is a TKA implant that provides for anterior stabilization in the absence of a surgically removed ACL while also accommodating a retained PCL. 
       INTRODUCTION TO THE INVENTION 
       [0015]    Currently, most TKA patients do not receive an implant that replaces the functionality of an absent ACL. Specifically, prior art implants do not resist anterior thrust of the femur relative to the tibia; and such resistance is needed to achieve optimal knee joint functionality. 
         [0016]    Referring to  FIG. 1 , a normal knee joint includes the ACL and PCL. For a normal joint, the ACL is operative to pull the femur anterior while the knee joint is moved toward full extension. Conversely, the PCL is operative to pull the femur posterior while the knee joint is moved toward full flexion. As can be seen in  FIG. 1 , the normal knee joint proximate full extension demonstrates the femur contacts the anterior aspect of the tibia and the patella is in contact with the femur. This is in stark contrast to the position of the femur and patella in a PCR TKA. 
         [0017]    Referring to  FIG. 2 , a PCR TKA allows the PCL to remain intact and to pull the femur in the posterior direction with flexion, but without the counteracting forces otherwise attributable to the ACL. In a PS TKA, the cam/post mechanisms force the femur in the posterior direction with increasing knee flexion, but from flexion to full extension anterior stabilization does not exist in present day total knee implant. At full extension, the femoral condyle of both PS and PCR TKA contact the tibial insert significantly more posterior than the normal knee, leading to patellar component separation from the femoral component and during activity, the femoral component remains posterior throughout the motion. 
         [0018]    The present knee implant system provides for joint motion that more closely mimics the proper function of a natural human knee in part by replacing the function of a healthy anterior cruciate ligament. In one embodiment, the knee implant comprises: a femoral component, the femoral component having a first surface attachable to a femur and a second surface wherein the second surface includes a pair of substantially parallel articular condyles with a slot therebetween, an anterior cam (symmetric, asymmetric, sloped, elongated, round, or variable shapes depending on the angle between the femur and the tibia) extending between the condyles and through the slot; a tibial component attachable to a tibia; and a bearing component disposed between the tibial component and the femoral component, the bearing component having a first surface attached to the tibial component and a second articulating surface that includes two recessed bearing surfaces such that the femoral component is rotatably and slidably engaged with the femoral component condyles, and wherein the bearing surfaces are separated by a spine protruding from between the bearing surfaces and wherein the spine engages with the cam at certain flexion angles of the knee implant such that the spine contacts the cam to force the femoral component in the anterior direction during extension. At full extension, this cam/post engagement will ensure that the femoral condyles contact the tibial insert on the anterior aspect. During flexion the cam will release from the post until engagement no longer exists. Then, the PCL will pull the femur in the posterior direction. The anterior cam/post mechanism will work in unison with the PCL to provide stability to the knee joint. Subjects having an AS TKA will experience an anterior thrust of the femoral component during extension activities, such as chair-rise, stair-climb and during walking. 
         [0019]    It is a first aspect of the present invention to provide a total knee implant prosthesis comprising: (a) a posterior retaining ligament femoral component including a pair of condyles interposed by an opening, the femoral component also including an anterior cam; and (b) a posterior retaining ligament tibial component, the tibial component including a post and a pair of condyle depressions. 
         [0020]    In a more detailed embodiment of the first aspect, the posterior retaining ligament tibial component includes a tibial tray and a tibial tray insert. In yet another more detailed embodiment, the tibial tray insert is a mobile bearing insert. In a further detailed embodiment, the tibial tray insert is a fixed bearing insert. In still a further detailed embodiment, the tibial tray insert includes the pair of condyle depressions, and the tibial tray includes the post. In a more detailed embodiment, the tibial tray insert includes the pair of condyle depressions, and the tibial tray insert includes the post. In a more detailed embodiment, the post is separable from both the tibial tray insert and the tibial tray. In another more detailed embodiment, the anterior cam is mobile bearing with respect to at least one of the pair of condyles. In still another more detailed embodiment, the anterior cam is fixed bearing with respect to the pair of condyles. 
         [0021]    In yet another more detailed embodiment of the first aspect, the tibial tray insert comprises independent pieces, a first independent piece includes a medial condyle depression of the pair of condyle depressions, and a second independent piece includes a lateral condyle depression of the pair of condyle depressions, wherein at least one of the first independent piece and the second independent piece is mobile bearing, with respect to the tibial tray. In still another more detailed embodiment, an anterior surface of the post is planar and substantially vertical. In a further detailed embodiment, an anterior surface of the post is sloped upward from anterior to posterior. In still a further detailed embodiment, an anterior surface of the post is substantially planar and angled to face toward a first of the pair of condyle depressions and away from a second of the pair of condyle depressions. In a more detailed embodiment, an anterior surface of the post includes a helical groove. In a more detailed embodiment, an anterior surface of the post includes a helical projection. In another more detailed embodiment, the helical projection is at least one of symmetrical and asymmetrical. In yet another more detailed embodiment, the helical projection is asymmetrical and a lateral portion of the helical projection protrudes outward on a lateral side more than on a medial side. 
         [0022]    In a more detailed embodiment of the first aspect, an anterior surface of the post is sloped upward from posterior to anterior. In yet another more detailed embodiment, an anterior surface of the anterior cam is rounded and substantially perpendicularly oriented with respect to the pair of condyles. In a further detailed embodiment, an anterior surface of the anterior cam is planar and angled to face toward a first of the pair of condyles and away from a second of the pair of condyles. In a more detailed embodiment, an anterior surface of the anterior cam is planar and substantially perpendicularly oriented with respect to the pair of condyles. In a more detailed embodiment, an anterior surface of the anterior cam is rounded and angled to face toward a first of the pair of condyles and away from a second of the pair of condyles. In another more detailed embodiment, an anterior surface includes a projection to be received within the helical groove in the post. In yet another more detailed embodiment, an anterior surface of the anterior cam includes a helical projection. In still another more detailed embodiment, the helical projection is at least one of symmetrical and asymmetrical. 
         [0023]    In yet another more detailed embodiment of the first aspect, the helical projection is asymmetrical and a lateral portion of the helical projection protrudes outward on a lateral side more than on a medial side. In still another more detailed embodiment, the post includes a base having a cross-section larger than a cross-section at a top of the post farthest from the tibial tray. In a further detailed embodiment, the tibial tray includes a projection that extends into an area bounded by the tibial tray insert, and the post is mounted to the projection. In still a further detailed embodiment, the post is fixed bearing with respect to the projection. In a more detailed embodiment, post is between 0.125 millimeters and 50 millimeters in length from anterior to posterior. In a more detailed embodiment, post is between 0.125 millimeters and 50 millimeters in width from medial to lateral. In another more detailed embodiment, post is between 0.125 millimeters and 50 millimeters in height from superior to inferior. In yet another more detailed embodiment, the anterior cam is resilient. 
         [0024]    In a more detailed embodiment of the first aspect, the anterior cam includes a shock absorber. In yet another more detailed embodiment, the anterior cam includes a spring. In a further detailed embodiment, the anterior cam includes at least two springs, where at least two of the springs have symmetrical spring coefficient. In still a further detailed embodiment, the anterior cam includes at least a medial spring and a lateral spring, where the medial spring and the lateral spring have asymmetrical spring rates. In a more detailed embodiment, a spring rate of the medial spring is lower than a spring rate of the lateral spring. In a more detailed embodiment, the post is resilient. In another more detailed embodiment, the post includes a shock absorber. In yet another more detailed embodiment, the post includes a spring. In still another more detailed embodiment, the post includes at least two springs, where at least two of the springs have symmetrical spring coefficient. 
         [0025]    In yet another more detailed embodiment of the first aspect, the post includes at least a medial spring and a lateral spring, where the medial spring and the lateral spring have asymmetrical spring rates. In still another more detailed embodiment, a spring rate of the medial spring is lower than a spring rate of the lateral spring. In a further detailed embodiment, at least one of the tibial tray and the tibial tray insert includes a projection, and the post includes a plurality of cavities, each of the plurality of cavities sized to separately accommodate at least a portion of the projection to secure the post to at least one of the tibial tray and the tibial tray insert. In still a further detailed embodiment, the post includes a projection, and at least one of the tibial tray and the tibial tray insert includes a plurality of cavities, each of the plurality of cavities adapted to house a portion of the projection to secure the post to at least one of the tibial tray and the tibial tray insert. In a more detailed embodiment, the anterior cam is at least one of inset with respect to the medial and lateral condyles, flush with respect to the medial and lateral condyles, and projects outward with respect to the medial and lateral condyles. In a more detailed embodiment, the femoral component includes a projection, and the anterior cam includes a plurality of cavities, each of the plurality of cavities sized to separately accommodate at least a portion of the projection to secure the anterior cam to the femoral component. In another more detailed embodiment, the anterior cam includes a projection, and the femoral component includes a plurality of cavities, each of the plurality of cavities sized to separately accommodate at least a portion of the projection to secure the anterior cam to the femoral component. 
         [0026]    It is a second aspect of the present invention to provide a posterior cruciate ligament retaining knee implant prosthesis comprising: (a) a femoral component including a medial condyle and a lateral condyle separated from one another by an intercondylar channel adapted to accommodate throughput of a native cruciate ligament, both the medial condyle and the lateral condyle posteriorly terminate individually, the medial condyle including a medial condyle bearing surface and the lateral condyle including a lateral condyle bearing surface, the femoral component including an anterior post; and (b) a tibial component including a medial condyle receiver having a medial condyle receiver bearing surface, the tibial component also including a lateral condyle receiver having a lateral condyle receiver bearing surface, the tibial component including an anterior cam. 
         [0027]    In a more detailed embodiment of the second aspect, the posterior retaining ligament tibial component includes a tibial tray and a tibial tray insert. In yet another more detailed embodiment, the tibial tray insert is a mobile bearing insert. In a further detailed embodiment, the tibial tray insert is a fixed bearing insert. In still a further detailed embodiment, the tibial tray insert includes the pair of condyle depressions, and the tibial tray includes the anterior cam. In a more detailed embodiment, the tibial tray insert includes the pair of condyle depressions, and the tibial tray insert includes the anterior cam. In a more detailed embodiment, the anterior cam is separable from both the tibial tray insert and the tibial tray. In another more detailed embodiment, the post is mobile bearing with respect to at least one of the pair of condyles. In still another more detailed embodiment, the post is fixed bearing with respect to the pair of condyles. 
         [0028]    In yet another more detailed embodiment of the second aspect, the tibial tray insert comprises independent pieces, a first independent piece includes a medial condyle depression of the pair of condyle depressions, and a second independent piece includes a lateral condyle depression of the pair of condyle depressions, wherein at least one of the first independent piece and the second independent piece is mobile bearing with respect to the tibial tray. In still another more detailed embodiment, an anterior surface of the post is planar and substantially vertical. In a further detailed embodiment, an anterior surface of the post is sloped upward from anterior to posterior. In still a further detailed embodiment, an anterior surface of the anterior cam is substantially planar and angled to face toward a first of the pair of condyle depressions and away from a second of the pair of condyle depressions. In a more detailed embodiment, an anterior surface of the post includes a helical groove. In a more detailed embodiment, an anterior surface of the post includes a helical projection. In another more detailed embodiment, the helical projection is at least one of symmetrical and asymmetrical. In yet another more detailed embodiment, the helical projection is asymmetrical and a lateral portion of the helical projection protrudes outward on a lateral side more than on a medial side. 
         [0029]    In a more detailed embodiment of the second aspect, an anterior surface of the post is sloped upward from posterior to anterior. In yet another more detailed embodiment, an anterior surface of the post is rounded and substantially perpendicularly oriented with respect to the pair of condyles. In a further detailed embodiment, an anterior surface of the post is planar and angled to face toward a first of the pair of condyles and away from a second of the pair of condyles. In a more detailed embodiment, an anterior surface of the post is planar and substantially perpendicularly oriented with respect to the pair of condyles. In a more detailed embodiment, an anterior surface of the post is rounded and angled to face toward a first of the pair of condyles and away from a second of the pair of condyles. In another more detailed embodiment, an anterior surface includes a projection to be received within the helical groove in the anterior cam in yet another more detailed embodiment, an anterior surface of the post includes a helical projection. In still another more detailed embodiment, the helical projection is at least one of symmetrical and asymmetrical. 
         [0030]    In yet another more detailed embodiment of the first aspect, the helical projection is asymmetrical and a lateral portion of the helical projection protrudes outward on a lateral side more than on a medial side. In still another more detailed embodiment, the post includes a base having a cross-section larger than a cross-section at a top of the post farthest from the femoral attachment location. In a further detailed embodiment, the tibial tray includes a projection that extends into an area bounded by the tibial tray insert, and the anterior cam is mounted to the projection. In still a further detailed embodiment, the anterior cam is fixed bearing with respect to the projection. In a more detailed embodiment, post is between 0.125 millimeters and 50 millimeters in length from anterior to posterior. In a more detailed embodiment, post is between 0.125 millimeters and 50 millimeters in width from medial to lateral. In another more detailed embodiment, post is between 0.125 millimeters and 50 millimeters in height from superior to inferior. In yet another more detailed embodiment, the anterior cam is resilient. 
         [0031]    In a more detailed embodiment of the second aspect, the anterior cam includes a shock absorber. In yet another more detailed embodiment, the anterior cam includes a spring. In a further detailed embodiment, the anterior cam includes at least two springs, where at least two of the springs have symmetrical spring coefficient. In still a further detailed embodiment, the anterior cam includes at least a medial spring and a lateral spring, where the medial spring and the lateral spring have asymmetrical spring rates. In a more detailed embodiment, a spring rate of the medial spring is lower than a spring rate of the lateral spring. In a more detailed embodiment, the post is resilient. In another more detailed embodiment, the post includes a shock absorber. In yet another more detailed embodiment, the post includes a spring. In still another more detailed embodiment, the post includes at least two springs, where at least two of the springs have symmetrical spring coefficient. 
         [0032]    In yet another more detailed embodiment of the second aspect, the post includes at least a medial spring and a lateral spring, where the medial spring and the lateral spring have asymmetrical spring rates. In still another more detailed embodiment, a spring rate of the medial spring is lower than a spring rate of the lateral spring. In a further detailed embodiment, at least one of the tibial tray and the tibial tray insert includes a projection, and the anterior cam includes a plurality of cavities, each of the plurality of cavities sized to separately accommodate at least a portion of the projection to secure the anterior cam to at least one of the tibial tray and the tibial tray insert. In still a further detailed embodiment, the anterior cam includes a projection, and at least one of the tibial tray and the tibial tray insert includes a plurality of cavities, each of the plurality of cavities adapted to house a portion of the projection to secure the anterior cam to at least one of the tibial tray and the tibial tray insert. In a more detailed embodiment, the post is at least one of inset with respect to the medial and lateral condyles, flush with respect to the medial and lateral condyles, and projects outward with respect to the medial and lateral condyles. In a more detailed embodiment, the femoral component includes a projection, and the post includes a plurality of cavities, each of the plurality of cavities sized to separately accommodate at least a portion of the projection to secure the post to the femoral component. In another more detailed embodiment, the post includes a projection, and the femoral component includes a plurality of cavities, each of the plurality of cavities sized to separately accommodate at least a portion of the projection to secure the post to the femoral component. 
         [0033]    It is a third aspect of the present invention to provide a total knee implant prosthesis comprising: (a) a posterior retaining ligament femoral component including a pair of condyles interposed by an opening to accommodate a posterior cruciate ligament, the femoral component also including an anterior cam; and (b) a posterior retaining ligament tibial component, the tibial component including a post and a pair of condyle depressions, where at least one of the anterior cam and the post is spring biased. 
         [0034]    It is a fourth aspect of the present invention to provide a posterior cruciate retaining total knee femoral implant prosthesis comprising a posterior retaining ligament femoral component including a pair of condyles interposed by an opening to accommodate a posterior cruciate ligament, the femoral component also including an anterior cam. 
         [0035]    It is a fifth aspect of the present invention to provide a posterior cruciate retaining total knee femoral implant prosthesis comprising a posterior retaining ligament femoral component including a pair of condyles interposed by an opening to accommodate a posterior cruciate ligament, the femoral component also including an anterior post. 
         [0036]    It is a sixth aspect of the present invention to provide a posterior cruciate retaining total knee tibial implant prosthesis comprising a posterior retaining ligament tibial component including the tibial component including a cam and a pair of condyle depressions. 
         [0037]    It is a seventh aspect of the present invention to provide a posterior cruciate retaining total knee tibial implant prosthesis comprising a posterior retaining ligament tibial component including the tibial component including a cam and a pair of condyle depressions. 
         [0038]    It is an eighth aspect of the present invention to provide a total knee implant prosthesis comprising: (a) a posterior retaining ligament femoral component including a pair of condyles interposed by an opening to accommodate a posterior cruciate ligament, the femoral component also including at least one projection extending from at least one of the condyles; and (b) a posterior retaining ligament tibial component, the tibial component including a pair of condyle depressions to receive the pair of condyles, at least one of the pair of condyle depressions includes at least one cavity, each of the at least one cavity adapted to receive one of the at least one projection from the femoral component. 
         [0039]    It is a ninth aspect of the present invention to provide a total knee implant prosthesis comprising: (a) a posterior retaining ligament femoral component including a pair of condyles interposed by an opening to accommodate a posterior cruciate ligament, the femoral component also including at least one cavity within at least one of the condyles; and (b) a posterior retaining ligament tibial component, the tibial component including a pair of condyle depressions to receive the pair of condyles, at least one of the pair of condyle depressions includes at least one projection, each of the at least one cavity adapted to receive one of the at least one projection from the tibial component. 
         [0040]    It is a tenth aspect of the present invention to provide a total knee implant prosthesis comprising: (a) a posterior retaining ligament femoral component including a medial condyle and a lateral condyle interposed by an opening to accommodate a posterior cruciate ligament, the medial condyle including at least one projection, and the lateral condyle including at least one projection; and (b) a posterior retaining ligament tibial component, the tibial component including a medial condyle receiver and a lateral condyle receiver correspondingly operative to receive the medial and lateral condyles, the medial condyle receiver including at least one cavity to receive the at least one projection of the medial condyle, the lateral condyle receiver including at least one cavity to receive the at least one projection of the lateral condyle. 
         [0041]    It is an eleventh aspect of the present invention to provide a total knee implant prosthesis comprising: (a) a posterior retaining ligament femoral component including a medial condyle and a lateral condyle interposed by an opening to accommodate a posterior cruciate ligament, the medial condyle including at least one cavity, and the lateral condyle including at least one cavity; and (b) a posterior retaining ligament tibial component, the tibial component including a medial condyle receiver and a lateral condyle receiver correspondingly operative to receive the medial and lateral condyles, the medial condyle receiver including at least one projection to be received within the at least one cavity of the medial condyle, the lateral condyle receiver including at least one projection to be received within the at least one cavity of the lateral condyle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]      FIG. 1  is an X-ray image of a human knee joint proximate full extension. 
           [0043]      FIG. 2  is an X-ray image of a prosthetic knee joint proximate full extension. 
           [0044]      FIGS. 3A-3D  are exemplary diagrams showing different degrees of flexion and extension of a natural knee and a corresponding placement of a prosthetic joint when certain flexion or extension occurs. 
           [0045]      FIG. 4  is an exploded view of a first exemplary embodiment of a posterior cruciate retaining replacement knee providing anterior stabilization. 
           [0046]      FIG. 5  is a bottom view of an exemplary femoral component in accordance with the present disclosure. 
           [0047]      FIG. 6  is a bottom view of another exemplary femoral component in accordance with the present disclosure. 
           [0048]      FIG. 7  is a bottom view of a further exemplary femoral component in accordance with the present disclosure. 
           [0049]      FIG. 8  is a bottom view of yet another exemplary femoral component in accordance with the present disclosure. 
           [0050]      FIG. 9  is a profile view of an exemplary distal component in accordance with the present disclosure. 
           [0051]      FIG. 10  is a profile view of another exemplary distal component in accordance with the present disclosure. 
           [0052]      FIG. 11  is a profile view of a further exemplary distal component in accordance with the present disclosure. 
           [0053]      FIG. 12  is a top view of an exemplary tibial tray insert in accordance with the present disclosure. 
           [0054]      FIG. 13  is a top view of another exemplary tibial tray insert in accordance with the present disclosure. 
           [0055]      FIG. 14  is a bottom view of still a further exemplary femoral component in accordance with the present disclosure. 
           [0056]      FIG. 15  is a top view of another exemplary femoral tibial tray insert in accordance with the present disclosure. 
           [0057]      FIG. 16  is a top view of yet another exemplary tibial tray insert in accordance with the present disclosure. 
           [0058]      FIG. 17  is a bottom view of another exemplary femoral component in accordance with the present disclosure. 
           [0059]      FIG. 18  is a top view of still a further exemplary tibial tray insert in accordance with the present disclosure. 
           [0060]      FIG. 19  is a profile view of an exemplary tibial component in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0061]    The exemplary embodiments of the present disclosure are described and illustrated below to encompass prosthetic knee joints and knee joint components, as well as methods of implanting and reconstructing knee joints. Of course, it will be apparent to those of ordinary skill in the art that the preferred embodiments discussed below are exemplary in nature and may be reconfigured without departing from the scope and spirit of the present invention. However, for clarity and precision, the exemplary embodiments as discussed below may include optional steps, methods, and features that one of ordinary skill should recognize as not being a requisite to fall within the scope of the present invention. 
         [0062]    Referencing  FIGS. 3A-3D , a series of representations are shown of a generic human anatomy below the torso comprising a femur  10  and a tibia  12  that represent the position of the femur with respect to the tibia as the knee joint  14  flexes.  FIG. 1A  shows the femur  10  and tibia  12  in axial alignment with respect to a TKA axis  16  when the knee joint  14  is in complete extension. Likewise,  FIG. 3A  also shows the common position of a femoral component  20  and a tibial component  22  that may be used in a total knee arthroplasty when the prosthetic knee joint is in full extension. 
         [0063]    Referring to  FIG. 3B , the knee joint  14  is at approximately 45 degrees of flexion. In this manner, the distal portion of the femur  10  has moved forward relative to the tibia, as has the proximal portion of the tibia  12 . Similarly, in the prosthetic knee joint, 45 degrees of flexion causes the tibial component  22  to shift forward with respect to the TKA axis  16  and takes on the angle of the remainder of the tibia. Likewise, the femoral component  20  also shifts forward with respect to the TKA axis  16 , but rolls backward (posteriorly) with respect to the tibial component  22  so that a more posterior portion of the condyles of the femoral component are seated within a more posterior portion of the tibial component. 
         [0064]    Referencing  FIG. 3C , continued flexion of the knee joint  14  to approximately 90 degrees results in further forward motion of the femur  10  and tibia  12  with respect to the TKA axis  16 . Consistent with this movement, the femoral component  20  and the tibial component  22  also are moved further forward with respect to the TKA axis  16 , but the femoral component continues to rotate posteriorly and move backward on the tibial component. 
         [0065]    Referencing  FIG. 3D , continued flexion of the knee joint  14  to maximum flexion of approximately 160 degrees results in maximum forward motion of the femur  10  and tibia  12  with respect to the TKA axis  16 . Consistent with this movement, the femoral component  20  and the tibial component  22  also are moved further forward with respect to the TKA axis  16  and the femoral component continues to rotate posteriorly and move rearward on the tibial component so that only the most posterior portion of the femoral component  20  remains in contact with the tibial component  22 . 
         [0066]    Referring  FIG. 4 , an exemplary posterior cruciate retaining orthopedic knee implant  100  for use with total arthroplasty procedures includes a femoral component  102  and a tibial component  104 . In this exemplary embodiment, the tibial component  104  comprises a tibial tray  106  and a tibial tray insert  108 . 
         [0067]    The exemplary posterior cruciate retaining orthopedic femoral component  102  includes a posterior discontinuity or gap  110  between lateral and medial condyles  112 ,  114  to allow the femoral component to rotate between maximum extension and maximum flexion without impinging the posterior cruciate ligament (PCL), which is retained. In contrast, the anterior cruciate ligament (ACL) is sacrificed or removed during a total arthroplasty procedure. Those skilled in the art are familiar with the posterior constraint resulting from retention of the posterior cruciate ligament, whereas those skilled in the art are also familiar with the absence of anterior constraint resulting from the absence of the anterior cruciate ligament. 
         [0068]    This exemplary femoral component  102  includes two condyles  112 ,  114  each having an arcuate shape in order to allow for smooth rotation of the femur with respect to the tibia. In general, the femoral component includes an anterior portion  116  and a posterior portion  118  that are shown by the dotted line imaginary boundary. The anterior portion  116  includes a front exterior face  120  having a depression  122  adapted to receive at least a portion of a patella component  123 . The depression  122  marks the beginning of individual condyle  112 ,  114  formation. From the top of the front face  120  downward, following the contours of the front face, the curved nature of begins to take shape and transition into individual condyles  112 ,  114 . As the shape of the condyles  112 ,  114  becomes more pronounced, the condyles separate from one another, which is marked by an arcuate bridge  124  formed at the most proximal connection point of the condyles. As the shape of the condyles  112 ,  114  continue more distal, past the arcuate bridge  124 , the condyles widen and generally flare out on the outer edges. At the same time, the bearing surfaces of the condyles  112 ,  114  flatten out and do not exhibit a uniform arcuate shape from anterior to posterior. However, the posterior discontinuity or gap  110  has a substantially uniform width, resulting in the inner shape and contour of the condyles being substantially the same. Unlike prior art posterior cruciate retaining femoral components, the exemplary posterior cruciate retaining femoral component  102  includes an anterior cam  126  that engages a post  128  of the tibial component  104 . 
         [0069]    Referring to  FIG. 5 , the anterior femoral cam  126  of the femoral component  102  may have various shapes. For example, an alternate anterior cam  126 ′ has a camming surface that is arcuate or rounded as a result of the cam having a cylindrical shape. Conversely, the anterior cam  126  could include a camming surface that is substantially flat where the cam is in the shape of a square or rectangular peg. 
         [0070]    Referring to  FIG. 6 , in a further alternate exemplary embodiment of the femoral component  102 , the anterior cam  126 ″ has an inclined arcuate or rounded camming surface as a result of the cam having a hybrid shape melding a cylindrical half with a conical half. Because the conical half faces the posterior direction, the conical half comprises the camming surface that interacts with the tibial post  128  (see  FIG. 4 ). In this exemplary embodiment, the camming surface has an inclined slope from the medial condyle  114  to the lateral condyle  112 . Conversely, the anterior cam could embody a trapezoidal shape having a substantially flat, but inclined to slope from the medial condyle  114  to the lateral condyle  112 . 
         [0071]    Referring to  FIG. 7 , in yet a further alternate exemplary embodiment of the femoral component  102 , the anterior cam  126 ″′ has a rounded, helical shape. In other words, the shape of the anterior cam  126 ″′ resembles a worm gear having a helical thread. In this exemplary embodiment, the helical thread increasing in thickness from medial to lateral. Accordingly, as the femoral component is rotated from anterior to posterior, the amount of camming surface contacting the tibial post  128  (see  FIG. 4 ) increases concurrently with increased axial rotation of the femoral component  102 . 
         [0072]    Referencing  FIG. 8 , in still a further alternate exemplary embodiment of the femoral component  102 ′, the anterior cam  126 ″″ has an arcuate or rounded camming surface that is biased to cushion the impact of the camming surface coming into contact with the tibial post  128  (see  FIG. 4 ). In this alternate exemplary embodiment of the femoral component  102 ′, the camming surface is embodied in a separate component  130  of the anterior cam  126 ″″ that is mounted to a cam retainer  132 , which is mounted to the remainder of the femoral component  102 ′. A pair of biasing members  134  interposes the camming surface component  130  and the cam retainer. In this exemplary embodiment, each biasing member  134  comprises a helical spring. However, alternate structures may be used in lieu of a helical spring including, without limitation, a resilient bushing or leaf spring. 
         [0073]    It is also within the scope of the invention that the medial biasing member  134 M and the lateral biasing member  134 L having different biasing strengths and/or be comprised of different structures or components. For example, the medial biasing member  134 M may comprise a titanium helical spring having a spring rate different than that the lateral biasing member  134 L, which comprises a stainless steel leaf spring. In exemplary form, the medial biasing member  134 M includes a spring rate substantially less than that of the lateral biasing member  134 L so that upon contact with the tibial post  128 , the medial biasing member  134 M compresses to a greater degree than the lateral biasing member  134 L, thus providing a camming surface that is accordingly inclined from the medial condyle  114  to the lateral condyle  112 . 
         [0074]    Referencing  FIGS. 4 and 9 , the exemplary tibial tray  106  includes a stem  141  that is adapted to be received within the intramedullary canal of the tibia. The stem  141  may be cemented or adapted for bone ingrowth to permanently mount the tibial tray  106  to the tibia. Integral with the stem  141  is a platform  142  on which the tibial tray insert  108  is mounted. In this regard, the tibial tray  106  may provide either a fixed bearing interface to lock the orientation of the tibial tray insert  108  with the tibial tray  106  or a mobile bearing interface that allows the tibial tray insert  108  to move independent of the tibial tray  106 . 
         [0075]    A first exemplary tibial tray  106  includes a first cylindrical projection  140  that extends upward from the platform  142  in a direction generally perpendicular to the face of the platform. This first cylindrical projection  140  is substantially centered from anterior-to-posterior and lateral-to-medial on the platform  142 . In exemplary form, the projection  140  is received within a cavity  152  extending through the tibial tray insert  108 , but not received so tightly as to inhibit rotation of the tibial tray insert with respect to the projection. It is the combination of the projection  140  and the cavity  152  that provides mobile bearing functionality for the tibial component  104 . As will be obvious to those skilled in the art, the cavity  152  and the projection  140  may be switched so that the platform  142  includes the cavity, while the tray insert  108  includes the projection. 
         [0076]    The tibial tray insert  108  also includes concave bearing surfaces  160 ,  162  that are adapted to receive the medial and lateral condyles  114 ,  112  of the femoral component  102 . The two concave bearing surfaces  160 ,  162  are partially separated from one another by a trapezoidal post  164  upstanding from the tibial tray insert  108 . In this exemplary embodiment, the post  164  is integrally formed with the tibial tray insert  108 . However, it is also within the scope of the invention that the post  164  is separable from the tibial tray insert  108  and its location is independent of the location/movement of the tibial tray insert. The post  164  includes an anterior wall  166  having a substantially vertical face and a posterior wall  168  having an inclined face from posterior to anterior. The vertical face of the anterior wall  166  is substantially parallel with the anterior-posterior centerline. The anterior wall  166  and posterior wall  168  are separated from one another by substantially vertical medial and lateral side walls  170 ,  172  and a horizontal top wall  174 . 
         [0077]    Referring to  FIG. 10 , an alternate exemplary fixed bearing tibial component  104 ′ includes a tibial tray  106 ′ and a tibial tray insert  108 ′. In this exemplary embodiment, the tibial tray  106 ′ includes a stem  141 ′ that is adapted to be received within the intramedullary canal of the tibia. The stem  141 ′ may be cemented or adapted for bone ingrowth to permanently mount the tibial tray  106 ′ to the tibia. Integral with the stem  141 ′ is a platform  142 ′ on which the tibial tray insert  108 ′ is mounted. 
         [0078]    The tibial tray insert  108 ′ also includes concave bearing surfaces  160 ′,  162 ′ that are adapted to receive the medial and lateral condyles  114 ,  112  of the femoral component  102  (see  FIG. 4 ). The two concave bearing surfaces  160 ′,  162 ′ are partially separated from one another by a trapezoidal post  164 ′ upstanding from the tibial tray insert  108 ′. In this exemplary embodiment, the post  164 ′ is integrally formed with the tibial tray insert  108 ′ and includes an anterior wall  166 ′ having a substantially vertical face and a posterior wall  168 ′ having an inclined face from posterior to anterior. The vertical face of the anterior wall  166 ′ is substantially parallel with the anterior-posterior centerline. The anterior wall  166 ′ and posterior wall  168 ′ are separated from one another by substantially vertical medial and lateral side walls  170 ′,  172 ′ and a horizontal top wall  174 ′. 
         [0079]    Referring to  FIG. 11 , a further alternate exemplary fixed bearing tibial component  104 ″ includes a tibial tray  106 ″ and a tibial tray insert  108 ″. In this exemplary embodiment, the tibial tray  106 ″ includes a stem  141 ″ that is adapted to be received within the intramedullary canal of the tibia. The stem  141 ″ may be cemented or adapted for bone ingrowth to permanently mount the tibial tray  106 ″ to the tibia. Integral with the stem  141 ″ is a platform  142 ″ on which the tibial tray insert  108 ″ is mounted. 
         [0080]    The tibial tray insert  108 ″ also includes concave bearing surfaces  160 ″,  162 ″ that are adapted to receive the medial and lateral condyles  114 ,  112  of the femoral component  102  (see  FIG. 4 ). The two concave bearing surfaces  160 ″,  162 ″ are partially separated from one another by a trapezoidal post  164 ″ upstanding from the tibial tray insert  108 ″. In this exemplary embodiment, the post  164 ″ is integrally formed with the tibial tray  106 ″. However, it is also within the scope of the invention that the post  164 ″ is separable from the tibial tray  106 ″ and correspondingly its location is not dependent upon the variable location of a mobile bearing tibial tray. The post  164 ″ includes an arcuate anterior wall  166 ″ having a substantially vertical face and a posterior conical wall  168 ″ having an arcuate, inclined face from posterior to anterior. The anterior wall  166 ″ and posterior wall  168 ″ are joined seamlessly to one another and transition at the top to a flat, substantially horizontal top wall  174 ″. 
         [0081]    Referencing  FIGS. 12 and 13 , an alternate exemplary tibial tray insert  184  for use in combination with the exemplary femoral components  102  includes a tibial post  180 ,  182  and adjacent medial and lateral condyles  186 ,  188 . The exemplary tibial post  180 ,  182 , in contrast to the foregoing exemplary tibial posts  164 , includes an anterior wall angled other than parallel with respect to the anterior-posterior centerline to the tibial tray insert  184 . 
         [0082]    Referring to  FIG. 12 , a first exemplary post  180  includes a generally trapezoidal shape exposed portion above the surface of the tibial tray insert  184 . The post comprises a flat, substantially vertical posterior surface  190  and flat, substantially vertical side surfaces  192 ,  194 . An anterior surface  196  is flat and substantially vertical, but is angled 20 degrees with respect to the anterior-posterior centerline. In other words, the leading or anterior edge on the lateral side of the post  180  is closer to the front of the tibial tray insert  184  than is the leading or anterior edge on the medial side of the post. In this manner, as the camming surface of the femoral component contacts the anterior face of the post  180 , the angle of the anterior surface cause the femoral component to rotate medially. 
         [0083]    Referring to  FIG. 13 , a second exemplary post  182  includes a generally trapezoidal shape exposed portion above the surface of the tibial tray insert  184 . The post comprises a flat, substantially vertical posterior surface  200  and flat, substantially vertical side surfaces  202 ,  204 . An anterior surface  206  is inclined from anterior-to-posterior and angled with respect to the anterior-posterior centerline of the tibial tray insert  184 . In this exemplary embodiment, the anterior surface is angled 20 degrees with respect to the anterior-posterior centerline and angled 70 degrees with respect to horizontal. In other words, the bottom corner of the anterior surface and the lateral side  188  is closer to the front of the tibial tray insert  184  than is the bottom corner of the anterior edge on the medial side of the post  182 . In this manner, as the camming surface of the femoral component contacts the anterior face of the post  180 , the angle and decline of the anterior surface cause the femoral component to rotate medially. 
         [0084]    Referring to  FIGS. 14-16 , a second exemplary posterior cruciate retaining orthopedic knee implant for use with total arthroplasty procedures includes a femoral component  302  and a tibial component  304 . In this exemplary embodiment, the tibial component  304  comprises a tibial tray (not shown) and a tibial tray insert  306 ,  308 . 
         [0085]    The exemplary posterior cruciate retaining orthopedic femoral component  302  include a posterior discontinuity or gap  310  between lateral and medial condyles  312 ,  314  to allow the femoral component to rotate between maximum extension and maximum flexion without impinging the posterior cruciate ligament, which is retained. Those skilled in the art are familiar with the posterior constraint resulting from retention of the posterior cruciate ligament, whereas those skilled in the art are also familiar with the absence of anterior constraint resulting from the absence of the anterior cruciate ligament. 
         [0086]    Referring specifically to  FIG. 14 , this exemplary femoral component  302  includes two condyles  312 ,  314  each having an arcuate shape in order to allow for smooth rotation of the femur with respect to the tibia. As the shape of the condyles  312 ,  314  becomes more pronounced, the condyles separate from one another, which is marked by an arcuate bridge  324  formed at the most proximal connection point of the condyles. As the shape of the condyles  312 ,  314  continues distally, past the arcuate bridge  324 , the condyles widen and generally flare out on the outer edges. At the same time, the bearing surfaces of the condyles  312 ,  314  flatten out and do not exhibit a uniform arcuate shape from anterior to posterior. However, the posterior discontinuity or gap  310  has a substantially uniform width, resulting in the inner shape and contour of the condyles being substantially the same. Unlike prior art posterior cruciate retaining femoral components, the exemplary posterior cruciate retaining femoral component  302  includes an anterior post  326  that engages a tibial cam  328  of the tibial component  304 . 
         [0087]    The anterior femoral post  326  of the femoral component  302  is mounted to a recessed bracket  330  extending between the condyles  312 ,  314  proximate the bridge  324 . In exemplary form, the femoral post  326  includes a rectangular cross-section and a sloped posterior face  332 . 
         [0088]    Referring to  FIG. 15 , the tibial component  304  may include a first exemplary tibial tray insert  306  having concave bearing surfaces  360 ,  362  that are adapted to receive the medial and lateral condyles  314 ,  312  of the femoral component  302 . The two concave bearing surfaces  360 ,  362  are partially separated from one another by the tibial cam  328  upstanding from the tibial tray insert  306 . In this exemplary embodiment, the cam  328  is integrally formed with the tibial tray insert  306 . However, it is also within the scope of the invention that the cam  328  is separable from the tibial tray insert  306  and correspondingly moves independent of the tibial tray insert. The cam  328  includes a rounded exterior surface  334 , which is angled other than perpendicular with respect to the anterior-posterior centerline. In this exemplary embodiment, the cam  328  is angled at 20 degrees with respect to the anterior-posterior centerline. 
         [0089]    Referring to  FIG. 16 , the tibial component  304  may include a second exemplary tibial tray insert  308  having concave bearing surfaces  360 ,  362  that are adapted to receive the medial and lateral condyles  314 ,  312  of the femoral component  302 . The two concave bearing surfaces  360 ,  362  are partially separated from one another by the tibial cam  328  upstanding from the tibial tray insert  306 . In this exemplary embodiment, the cam  328  is integrally formed with the tibial tray insert  306 . However, it is also within the scope of the invention that the cam  328  is separable from the tibial tray insert  306  and correspondingly moves independent of the tibial tray insert. The cam  328  includes a rounded exterior surface  334 , which is perpendicularly angled with respect to the anterior-posterior centerline. 
         [0090]    In operation, the femoral post  326  and tibial cam  328  work together to anteriorly stabilize the orthopedic knee replacement joint. Presuming a range of motion starting at fully flexion, the condyles  312 ,  314  of the femoral component  302  rotate from posterior to anterior so that eventually the posterior face  332  of the post  326  engages the anterior rounded exterior surface  334  of the femoral cam  328  to anteriorly stabilize the knee joint at near full extension up through full extension. When the femoral component  302  is rotated from anterior to posterior from full extension toward full flexion, the femoral post  326  gradually disengages against the tibial cam  326  so that posterior stability is provided by the retained posterior cruciate ligament at near full flexion toward full flexion. 
         [0091]    In the circumstance where the femoral post  326  is angled toward the medial condyle  362 , presuming a range of motion starting at fully flexion, the condyles  312 ,  314  of the femoral component  302  rotate from posterior to anterior so that eventually the posterior face  332  of the post  326  engages the anterior rounded exterior surface  334  of the femoral cam  328  on the lateral side and rotates the femoral component  302  medially combined with anterior stabilization the knee joint at near full extension up through full extension. Continued extension beyond initial engagement between the femoral post  326  and the tibial cam  328  results in more pronounced rotation so that eventually the femoral post  326  rides square upon the tibial cam  328  at maximum extension. When the femoral component  302  is rotated from anterior to posterior from full extension toward full flexion, the femoral post  326  gradually disengages against the tibial cam  326  combined with lateral rotation of the femoral component  302  so that posterior stability is provided by the retained posterior cruciate ligament at near full flexion toward full flexion. 
         [0092]    Referring to  FIGS. 17 and 18 , a third exemplary posterior cruciate retaining orthopedic knee implant for use with total arthroplasty procedures includes a femoral component  402  and a tibial component (not totally shown). In this exemplary embodiment, the tibial component comprises a tibial tray (not shown) and a tibial tray insert  406 . The exemplary posterior cruciate retaining orthopedic femoral component  402  include a posterior discontinuity or gap  410  between lateral and medial condyles  412 ,  414  to allow the femoral component to rotate between maximum extension and maximum flexion without impinging the posterior cruciate ligament, which is retained. Those skilled in the art are familiar with the posterior constraint resulting from retention of the posterior cruciate ligament, whereas those skilled in the art are also familiar with the absence of anterior constraint resulting from the absence of the anterior cruciate ligament. 
         [0093]    Referring specifically to  FIG. 17 , this exemplary femoral component  402  includes two condyles  412 ,  414  each having an arcuate shape in order to allow for smooth rotation of the femur with respect to the tibia. As the shape of the condyles  412 ,  414  becomes more pronounced, the condyles separate from one another, which is marked by an arcuate bridge  424  formed at the most proximal connection point of the condyles. As the shape of the condyles  412 ,  414  continues distally, past the arcuate bridge  424 , the condyles widen and generally flare out on the outer edges. At the same time, the bearing surfaces of the condyles  412 ,  414  flatten out and do not exhibit a uniform arcuate shape from anterior to posterior. However, unlike prior art posterior cruciate retaining femoral components, the exemplary posterior cruciate retaining femoral component  402  includes a lateral condyle cylindrical projection  426  and a medial condyle cylindrical projection  428 . 
         [0094]    Referring to  FIG. 18 , the tibial tray insert  406  includes lateral and medial condyle receivers  434 ,  436  that are adapted to receive the lateral and medial condyles  412 ,  414  of the femoral component  402 . In exemplary form, each of the condyle receivers includes a corresponding cavity  430 ,  432  adapted to receive the condyle projections  426 ,  428  of the femoral component. 
         [0095]    In operation, the femoral projections  426 ,  428  and tibial cavities  430 ,  432  work together to anteriorly stabilize the orthopedic knee replacement joint. Presuming a range of motion starting at fully flexion, the condyles  412 ,  414  of the femoral component  402  rotate from posterior to anterior so that eventually the lateral projection  426  on the lateral condyle  412  engages the lateral cavity  430  in the lateral condyle receiver  434  to inhibit sliding of the lateral condyle with respect to the lateral condyle receiver. Continued rotation  334  of the femoral component  402  with respect to the tibial tray insert  406  causes the femoral component to pivot about the lateral condyle receiver cavity  430  so that the femoral component rotates medially until the medial condyle projection  428  is received within the medial condyle cavity  432 . The corresponding inhabitation of sliding as the femoral component  402  is rotated provides anterior stability as the knee joint is near full extension through full extension. Conversely, as the femoral component  402  is rotated from anterior to posterior from full extension toward full flexion, the femoral condyle projections  426 ,  428  disengage from the cavities  430   432  of the tibial tray insert  406  so that posterior stability is provided by the retained posterior cruciate ligament at near full flexion toward full flexion. 
         [0096]    Referring to  FIG. 19 , an exemplary tibial component  500  includes a tibial tray insert  502  mounted to a tibial tray  504 . In this exemplary tibial component, an anterior post  506  is mounted to either the tibial tray insert  502  or the tibial tray  504  so that an anterior cam of a femoral component (not shown) engages the post to pull the femur anterior with respect to the tibia. The exemplary post  506  includes a posterior aspect  508  and an anterior aspect  510  that are interposed by a resilient material or one or more springs  512 . In this exemplary embodiment, the post  506  includes a pair of springs  512 , one on the medial side and one on the lateral side. More specifically, the spring rate of the medial spring is less than the spring rate of the lateral spring so that contact with the anterior cam of the femoral component is operative to push the anterior aspect  510  on the medial side more posterior than the lateral side of the anterior aspect. It is to be understood, however, that only one or more than two springs may be utilized. In addition, when multiple springs are utilized, the spring rates may be uniform or varied. In addition or in lieu of springs, resilient materials may be utilized that have different compression ratings or the same material may be utilized. Those skilled in the art will understand the plethora of options available by using a resilient material or a spring to interpose the anterior and posterior aspects of the tibial post. 
         [0097]    The exemplary femoral components of the exemplary embodiments may be fabricated from a hard and durable biocompatible material such as a titanium alloy, cobalt chrome alloy, alumina ceramic or zirconia ceramic. However, those of skill in the art will appreciate that any material can be used for this or the other components of a total knee implant while remaining within the scope of the present invention. 
         [0098]    The exemplary tibial components may be fabricated from a biocompatible material such as, without limitation, polyethylene, ultra high molecular weight polyethylene, highly cross-linked ultra high molecular weight polyethylene, a ceramic, and any biocompatible metal. 
         [0099]    While the foregoing exemplary embodiments have been described to have a separable tibial tray and a tibial tray insert, it is to be understood that the tibial tray may include condyle receiver bearing surfaces that obviate the need for a separate tibial tray insert. 
         [0100]    Following from the above description and invention summaries, it should be apparent to those of ordinary skill in the art that, while the methods and apparatuses herein described constitute exemplary embodiments of the present invention, the invention contained herein is not limited to this precise embodiment and that changes may be made to such embodiments without departing from the scope of the invention as defined by the claims. Additionally, it is to be understood that the invention is defined by the claims and it is not intended that any limitations or elements describing the exemplary embodiments set forth herein are to be incorporated into the interpretation of any claim element unless such limitation or element is explicitly stated. Likewise, it is to be understood that it is not necessary to meet any or all of the identified advantages or objects of the invention disclosed herein in order to fall within the scope of any claims, since the invention is defined by the claims and since inherent and/or unforeseen advantages of the present invention may exist even though they may not have been explicitly discussed herein.