Anterior stabilized knee implant

This invention relates to orthopaedic knee prostheses and, more specifically, to anterior stabilized orthopaedic knee prostheses for use with posterior cruciate retaining total knee arthroplasty procedures.

The closest prior art is document <patcit id="pcit0001" dnum="WO2005072657A1"><text>WO 2005/072657 A1</text></patcit>, which defines the preamble of claim 1.

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.

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.

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 close to zero in a healthy knee.

Normally, all of these components work in harmony. But disease or injury can disrupt this harmony, resulting in pain, muscle weakness, and reduced function.

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.

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.

Total knee replacement (TKR), also referred to as total knee arthroplasty (TKA), is a surgical procedure where worn, 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.

An artificial knee joint or prosthesis generally has three components: (1) a distal femoral component usually made of a biocompatible material such as metal alloys of cobalt and chromium 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.

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.

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.

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.

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 orthopaedic 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.

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.

Currently, most TKA patients do not receive an implant that replaces the functionality of an absent ACL. Specifically, known implants do not resist anterior thrust of the femur relative to the tibia, and such resistance is needed to achieve optimal knee joint functionality.

Referring to <figref idref="f0001">FIG. 1</figref>, 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 <figref idref="f0001">FIG. 1</figref>, 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.

Referring to <figref idref="f0001">FIG. 2</figref>, 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.

The present invention is defined in claim 1 and describes a total knee implant prosthesis that 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.

Optionally, an anterior surface of the post is planar and substantially vertical. Optionally, an anterior surface of the post is sloped upward from anterior to posterior.

Optionally, an anterior surface of the post is sloped upward from posterior to anterior. Optionally, an anterior surface of the anterior cam is rounded and substantially perpendicularly oriented with respect to the pair of condyles. Optionally, 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. Optionally, an anterior surface of the anterior cam is planar and substantially perpendicularly oriented with respect to the pair of condyles. Optionally, 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.

Embodiments of the invention are described below with reference to the accompanying drawings, in which: <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">FIG. 1</figref> is a representation based on an X-ray image of a human knee joint at close to full extension.</li><li><figref idref="f0001">FIG. 2</figref> is a representation based on an X-ray image of a prosthetic knee joint at close to full extension.</li><li><figref idref="f0002">FIGS. 3A-3D</figref> are diagrams showing different degrees of flexion and extension of a natural knee and a corresponding placement of a knee joint prosthesis when certain flexion or extension occurs.</li><li><figref idref="f0003">FIG. 4</figref> is an exploded view of a posterior cruciate retaining replacement knee providing anterior stabilization.</li><li><figref idref="f0004">FIG. 5</figref> is a bottom view of a femoral component.</li><li><figref idref="f0005">FIG. 6</figref> is a bottom view of another femoral component.</li><li><figref idref="f0006">FIG. 7</figref> is a bottom view of a further femoral component.</li><li><figref idref="f0007">FIG. 8</figref> is a bottom view of yet another femoral component.</li><li><figref idref="f0008">FIG. 9</figref> is a profile view of a distal component.</li><li><figref idref="f0009">FIG. 10</figref> is a profile view of another distal component.</li><li><figref idref="f0010">FIG. 11</figref> is a profile view of a further distal component.</li><li><figref idref="f0011">FIG. 12</figref> is a top view of a tibial tray insert.</li><li><figref idref="f0012">FIG. 13</figref> is a top view of another tibial tray insert.</li><li><figref idref="f0013">FIG. 14</figref> is a bottom view of still a further femoral component.</li><li><figref idref="f0014">FIG. 15</figref> is a top view of another femoral tibial tray insert.</li><li><figref idref="f0015">FIG. 16</figref> is a top view of yet another tibial tray insert.</li><li><figref idref="f0016">FIG. 17</figref> is a bottom view of another femoral component.</li><li><figref idref="f0017">FIG. 18</figref> is a top view of still a further tibial tray insert.</li><li><figref idref="f0018">FIG. 19</figref> is a profile view of an exemplary tibial component.</li></ul>

Referring to the drawings, <figref idref="f0002">FIGS. 3A to 3D</figref> are a series of representations 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. <figref idref="f0001">FIG. 1A</figref> 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, <figref idref="f0002">FIG. 3A</figref> 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.

Referring to <figref idref="f0002">FIG. 3B</figref>, 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.

Referring to <figref idref="f0002">FIG. 3C</figref>, 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.

As shown in <figref idref="f0002">FIG. 3D</figref>, 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.

<figref idref="f0003">FIG. 4</figref> shows a posterior cruciate retaining orthopaedic knee implant 100 for use with total arthroplasty procedures includes a femoral component 102 and a tibial component 104. In this embodiment, the tibial component 104 comprises a tibial tray 106 and a tibial tray insert 108.

The exemplary posterior cruciate retaining orthopaedic 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. Retention of the posterior cruciate ligament provides posterior constraint. Sacrificing the anterior cruciate ligament means that there is no anterior constraint.

The femoral component 102 shown in <figref idref="f0003">FIG. 4</figref> 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.

Referring to <figref idref="f0004">FIG. 5</figref>, 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.

Referring to <figref idref="f0005">FIG. 6</figref>, in a further example 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 <figref idref="f0003">FIG. 4</figref>). In this example, 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.

Referring to <figref idref="f0006">FIG. 7</figref>, in a further example 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 example, 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 <figref idref="f0003">FIG. 4</figref>) increases concurrently with increased axial rotation of the femoral component 102.

Referring to <figref idref="f0007">FIG. 8</figref>, in a further example of the femoral component 102', the anterior cam 126"" has an arcuate or rounded camming surface that is biassed to cushion the impact of the camming surface coming into contact with the tibial post 128 (see <figref idref="f0003">FIG. 4</figref>). In this example of the femoral component 102', the camming surface is embodied in a separate component 130 of the anterior cam126"" that is mounted to a cam retainer 132, which is mounted to the remainder of the femoral component 102'. A pair of biassing members 134 interposes the camming surface component 130 and the cam retainer. In this example, each biassing member 134 comprises a helical spring. However, alternate structures may be used instead of a helical spring including for example a resilient bushing or leaf spring.

It is also envisaged that the medial biassing member 134M and the lateral biassing member 134L having different biassing strengths and/or be comprised of different structures or components. For example, the medial biassing member 134M may comprise a titanium helical spring having a spring rate different than that the lateral biassing member 134L, which comprises a stainless steel leaf spring. For example, the medial biassing member 134M includes a spring rate substantially less than that of the lateral biassing member 134L so that upon contact with the tibial post 128, the medial biassing member 134M compresses to a greater degree than the lateral biassing member 134L, thus providing a camming surface that is accordingly inclined from the medial condyle 114 to the lateral condyle 112.

Referring to <figref idref="f0003">FIGS. 4</figref> and <figref idref="f0008">9</figref>, 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.

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 centred from anterior-to-posterior and lateral-to-medial on the platform 142. Preferably, 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. It will be apparent that 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.

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 example, the post 164 is integrally formed with the tibial tray insert 108. However, it is also envisaged 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.

Referring to <figref idref="f0009">FIG. 10</figref>, a fixed bearing tibial component 104' includes a tibial tray 106' and a tibial tray insert 108'. In this example, 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.

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 <figref idref="f0003">FIG. 4</figref>). 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 example, 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'.

Referring to <figref idref="f0010">FIG. 11</figref>, a fixed bearing tibial component 104" includes a tibial tray 106" and a tibial tray insert 108". In this example, 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.

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 <figref idref="f0003">FIG. 4</figref>). 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 example, the post 164" is integrally formed with the tibial tray 106". However, it is envisaged 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".

Referring to <figref idref="f0011">FIGS. 12</figref> and <figref idref="f0012">13</figref>, an alternate exemplary tibial tray insert 184 for use in combination with the femoral components 102 includes a tibial post 180, 182 and adjacent medial and lateral condyles 186, 188. The tibial post 180,182, in contrast to the tibial posts 164 referred to above, includes an anterior wall arranged other than parallel with respect to the anterior-posterior centerline to the tibial tray insert 184.

Referring to <figref idref="f0011">FIG. 12</figref>, a first 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 arranged at an angle of about 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.

Referring to <figref idref="f0012">FIG. 13</figref>, a second exemplary post 182 has 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 example, the anterior surface is arranged at an angle of about 20 degrees with respect to the anterior-posterior centerline and arranged at an angle of about 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.

Referring to <figref idref="f0013 f0014 f0015">FIGS. 14 to 16</figref>, a second posterior cruciate retaining orthopaedic knee implant for use with total arthroplasty procedures includes a femoral component 302 and a tibial component 304. In this embodiment, the tibial component 304 comprises a tibial tray (not shown) and a tibial tray insert 306, 308.

The posterior cruciate retaining orthopaedic femoral component 302 has a posterior discontinuity or gap 310 between the 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. Retention of the posterior cruciate ligament provides posterior constraint. Sacrificing the anterior cruciate ligament means that there is no anterior constraint.

Referring specifically to <figref idref="f0013">FIG. 14</figref>, this 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.

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. Preferably, the femoral post 326 has a rectangular cross-section and a sloped posterior face 332.

Referring to <figref idref="f0014">FIG. 15</figref>, 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 example, the cam 328 is integrally formed with the tibial tray insert 306. However, it is also envisaged 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 arranged other than perpendicular with respect to the anterior-posterior centerline. In this example, the cam 328 is arranged at an angle of about 20 degrees with respect to the anterior-posterior centerline.

Referring to <figref idref="f0015">FIG. 16</figref>, 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 example, the cam 328 is integrally formed with the tibial tray insert 306. However, it is also envisaged 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 approximately perpendicular to the anterior-posterior centerline.

In operation, the femoral post 326 and tibial cam 328 work together to anteriorly stabilize the orthopaedic 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.

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.

Referring to <figref idref="f0016">FIGS. 17</figref> and <figref idref="f0017">18</figref>, a third posterior cruciate retaining orthopaedic knee implant for use with total arthroplasty procedures includes a femoral component 402 and a tibial component (not totally shown). In this example, the tibial component comprises a tibial tray (not shown) and a tibial tray insert 406. The posterior cruciate retaining orthopaedic femoral component 402 has 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. Retention of the posterior cruciate ligament provides posterior constraint. Sacrificing the anterior cruciate ligament means that there is no anterior constraint.

Referring specifically to <figref idref="f0016">FIG. 17</figref>, this 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 known posterior cruciate retaining femoral components, the posterior cruciate retaining femoral component 402 includes a lateral condyle cylindrical projection 426 and a medial condyle cylindrical projection 428.

Referring to <figref idref="f0017">FIG. 18</figref>, 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. Each of the condyle receivers can include a corresponding cavity 430, 432 adapted to receive the condyle projections 426, 428 of the femoral component.

In operation, the femoral projections 426, 428 and tibial cavities 430, 432 work together to anteriorly stabilize the orthopaedic knee replacement joint. Presuming a range of motion starting at full 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.

Referring to <figref idref="f0018">FIG. 19</figref>, a tibial component 500 includes a tibial tray insert 502 mounted to a tibial tray 504. In this 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 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 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 different numbers of springs might be used, for example, one, two or more springs. In addition, when multiple springs are used, the spring rates may be uniform or varied. In addition or instead of springs, resilient materials may be used that have different compression ratings or the same material may be utilized. It will be understood that many options are available by using a resilient material or a spring to interpose the anterior and posterior aspects of the tibial post.

The femoral components may be fabricated from a hard and durable biocompatible material such as a titanium alloy, a cobalt chromium alloy, an alumina-based ceramic or a zirconia-based ceramic. It will be appreciated that any material can be used for this and other components of a total knee implant.

The tibial components may be fabricated from a biocompatible material such as for example polyethylene, ultra high molecular weight polyethylene, highly cross-linked ultra high molecular weight polyethylene, a ceramic, and any biocompatible metal.

While the examples described above 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 mean that a separate tibial tray insert is necessary.