Lateral and medial pivoting knee prosthesis

A method of stabilizing a knee comprising:

• mounting a prosthesis for replacing at least a portion of a knee joint between the distal end of a femur and the proximal end of a tibia wherein the prosthesis comprises:
• (a) a femoral component for mounting to a distal end of a femur comprises a lateral condyle and a medial condyle, each condyle having a major radius and a minor radius for a total of four condylar radii on the femoral component;
• wherein
• 1. the major radii of both condyles on the femoral component are located on a distal surface of the condyles with the major radius of the lateral condyle being equal to or up to 30 percent smaller than the major radius in the medial condyle;
• and
• 2. the minor radii are located posteriorly on the femoral component with the minor radius of the lateral condyle being equal to or up to 30 percent smaller than the minor radius on the medical condyle;
• (b) a tibial plate having medial and lateral sides comprising:
• 1. two tibial hemispherical recesses corresponding to the minor medial and major lateral radii lying medially and laterally, each recess is located in a posterior one third of the tibial plate;
• wherein these posterior recesses provide lateral and medial stable pivot points with the femoral condyles during knee flexion beginning with lateral axial pivoting in a first half of the flexion cycle and finishing a second half of the knee flexion cycle with medial axial pivoting;
• 2. Two oblong tibial plate recesses forming a trough and located in a medial and anterior two thirds of the tibial plate's proximal surface;
• wherein the anterior recesses are for the femoral condyle to smoothly translate forward rotating around the lateral and medial stable pivot points creating external rotation of the femur on the tibia during the first half of the knee flexion cycle and internal rotation of the femur during the second half of the knee flexion cycle;
• 3. wherein the lateral tibial hemispherical recess is maximally congruent to the major radius of the lateral femoral condyle engaging in early flexion providing the stable lateral pivot point for external femoral rotation during the first half of knee flexion for higher load activities;
• 4. wherein a portion of the hemispherical medial tibial recess is maximally congruent to the minor radius of the medial femoral condyle during the second half of the flexion cycle providing the stable medial pivot point for the internal femoral rotation required for high flexion activities;
• wherein on the medial side, a trough surface is congruent with the major radius of the medial condyle during early flexion as it translates anteriorly allowing the femur to externally rotate, engaging patella/quadriceps power in early flexion;
• and
• 5. laterally, the anterior oblong tibial recess is congruent with the minor radius of the lateral femoral condyle as it translates anteriorly during the second half of knee flexion when the stable pivot point has shifted from lateral to medial causing the femur to rotate back internally for the high flexion activities;
• (c) wherein at less than 75 degrees of flexion, the major radii of both of the lateral and medial femoral condyles are in contact with the lateral and medial tibial troughs such that in a lateral knee compartment there is maximal congruency between the lateral posterior hemispherical recess and the major radius of the lateral femoral condyle providing the stable lateral pivot point and medially there is smooth contact and anterior translation between femoral condyle and the trough creating the external rotation of the femur placing a femoral-patellar groove on the femur in contact with a patella of the knee;
• (d) wherein at flexion greater than 75 degrees the minor radius of the lateral femoral condyle now begins to translate forward in the anterior oblong lateral recess while the medial femoral condyle translates posteriorly and assumes maximal congruency with the minor medial condyle radius thereby allowing the medial condyle to assume the medial stable pivot point during this second half of the flexion cycle creating the internal femoral rotation required for the high flexion activities;
• (e) wherein during the first half of the flexion cycle, the lateral and medial condyles rotate against the tibial plate;
• and
• (f) wherein during the second half of the flexion cycle, the lateral condyle slides anteriorly in the tibial plate.

A knee prosthesis for replacing a portion of a knee joint between a distal end of a femur and a proximal end of a tibia, the knee prosthesis comprising:

• (a) a femoral component for mounting to the distal end of the femur comprises a lateral condyle and a medial condyle, each condyle having a major radius and a minor radius for a total of four condylar radii on the femoral component;
• 1. the major radii of both condyles on the femoral component are located on a distal surface of the condyles with the major radius of the lateral condyle being equal to or up to 30 percent smaller than the major radius in the medial condyle;
• and
• 2. the minor radii are located posteriorly on the femoral component with the minor lateral condyle radius being equal to or up to 30 percent smaller than a minor radius on the medial condyle;
• (b) a tibial plate for mounting to the proximal end of the tibia having medial and lateral sides, two troughs which run anterior to posterior which correspond to the lateral and medial condyles of the femoral component;
• wherein the tibial plate comprises:
• 1. two tibial hemispherical plate recesses corresponding to the minor medial and major lateral radii lying medially and laterally, wherein each recess is located in a posterior one third of the tibial plate;
• wherein the two tibial hemispherical plate recesses provide lateral and medial stable pivot points with the femoral condyles during knee flexion beginning with lateral axial pivoting in a first half of the knee flexion cycle and finishing a second half of the knee flexion cycle with medial axial pivoting;
• 2. Two oblong tibial plate recesses located in a medial and anterior two thirds of a proximal surface of the tibial plate;
• wherein the two oblong tibial plate recesses are for the femoral condyle to smoothly translate forward rotating around the lateral and medial stable pivot points creating external rotation of the femur on the tibia during the first half of the knee flexion cycle and internal rotation of the femur during the second half of the knee flexion cycle;
• 3. wherein the lateral tibial hemispherical recess is maximally congruent to the major radius of the lateral femoral condyle engaging in early knee flexion providing the stable lateral pivot point for external femoral rotation during the first half of knee flexion for higher load activities;
• 4. Wherein the medial trough is maximally congruent to the minor radius of the medial femoral condyle during the second half of the knee flexion cycle providing the stable medial pivot point for the internal femoral rotation required for high knee flexion activities;
• wherein on the medial side, the medial trough is congruent with the major radius of the medial condyle during early knee flexion as it translates anteriorly allowing the femur to externally rotate, engaging patella/quadriceps power in early knee flexion;
• and
• 5. laterally, the anterior tibial trough is congruent with the minor radius of the lateral femoral condyle as it translates anteriorly during the second half of knee flexion when the stable pivot point has shifted from lateral to medial causing the femur to rotate back internally for the high knee flexion activities;
• (c) wherein at less than 75 degrees of knee flexion, the major radii of both of the lateral and medial femoral condyles are in contact with the lateral and medial tibial troughs such that in a lateral knee compartment there is maximal congruency between the lateral posterior hemispherical recess and the major radius of the lateral femoral condyle providing the stable lateral pivot point and medially there is smooth contact and anterior translation between the femoral condyle and the trough creating the external rotation of the femur placing a femoral-patellar groove on the femur in contact with a patella of the knee;
• and
• (d) wherein at knee flexion greater than 75 degrees the minor radius of the lateral femoral condyle now begins to translate forward in the anterior lateral recess while the medial femoral condyle translates posteriorly and assumes maximal congruency with the minor medial condyle radius thereby allowing the medial condyle to assume the medial stable pivot point during this second half of the knee flexion cycle creating the internal femoral rotation required for the high knee flexion activities.