Prosthesis and method for using prosthesis to facilitate deep knee flexion

Abstract

The present invention provides a femoral prosthesis for a femur which can enable or allow deep knee flexion without creating excessive tension in the ligamentous structure of the knee. The femoral prosthesis includes an internal non-articulating surface, an external articulating surface, a medial condyle and a lateral condyle. The height of the medial condyle is less than the height of the lateral condyle. A proximal-posterior tip of the medial condyle is rounded and is shifted inwards relative to the native level of the proximal-posterior region of the femur bone to facilitate knee flexion. A method of mounting a femoral prosthesis on a femur is also described.

1 . A femoral prosthesis comprising:
 an internal non-articulating bone-engaging surface configured to be connected to a resected distal end of a femur;   an external articulating surface including a distal articulating surface, a medial posterior surface having a first medial end and a second medial end, and a lateral posterior surface having a first lateral end and a second lateral end, wherein the first medial end and the first lateral end are connected to the distal articulating surface;   a medial condyle extending from the first medial end to the second medial end and formed between the medial posterior surface and the internal non-articulating surface; and   a lateral condyle extending from the first lateral end to the second lateral end and formed between the lateral posterior surface and the internal non-articulating surface;   wherein a first height of the medial condyle measured from a line tangent to the distal articulating surface to the second medial end is less than a second height of the lateral condyle measured from the line tangent to the distal articulating surface to the second lateral end, and   wherein the medial collateral ligament in a knee with the prosthesis does not experience increased tension as the knee is flexed, even for flexion of the knee beyond 90 degrees.   
     
     
         2 . The femoral prosthesis of  claim 1 , wherein:
 removal of a proximal-posterior bone allows the femoral prosthesis to avoid contact with a tibial component.   
     
     
         3 . The femoral prosthesis of  claim 1  wherein:
 the femoral prosthesis allows the knee to go into deep flexion without having to overstretch soft-tissue, thereby enhancing the range of motion of the femoral prosthesis. 
 
     
     
         4 . The femoral prosthesis of  claim 1 , wherein:
 the femoral prosthesis maintains symmetric medial and lateral ligament balance through a full range of motion without overstretching the soft-tissue in the knee.   
     
     
         5 . The femoral prosthesis of  claim 1 , wherein:
 tension in posterior cruciate ligament (PCL) is significantly reduced for knee flexion above 90 degrees thereby minimizing soft tissue tightness in flexion on the medial side and soft tissue attaching to the medial femoral condyle.   
     
     
         6 . The femoral prosthesis of  claim 1 , wherein a radius of the medial condyle is less than a radius of the lateral condyle. 
     
     
         7 . The femoral prosthesis of  claim 1 , wherein the medial condyle further includes a proximal-posterior tip or end, the proximal-posterior tip or end having a smooth rounded profile. 
     
     
         8 . The femoral prosthesis of  claim 1 , wherein a difference in height between the medial condyle and the lateral condyle is within the range of about 2 millimeters to about 5 millimeters. 
     
     
         9 . The femoral prosthesis of  claim 1 , wherein the medial posterior surface transitions from a posterior portion in which the medial posterior surface is not shifted inwards relative to the lateral posterior surface to a distal-posterior portion in which the medial posterior surface is shifted inwards relative to the lateral posterior surface. 
     
     
         10 . The femoral prosthesis of  claim 1 , wherein:
 the medial posterior surface transitions from a posterior portion in which the medial posterior surface is not shifted inwards relative to the lateral posterior surface to a proximal-posterior portion in which the medial posterior surface is shifted inwards relative to the lateral posterior surface, such that a posterior thickness of the medial condyle measured from the internal non-articulating bone-engaging surface is equal to a posterior thickness of the lateral condyle.   
     
     
         11 . A method for mounting a femoral prosthesis on a distal end of a femur, the method comprising:
 providing a femoral prosthesis with a distal articulating surface and a posterior articulating surface;   removing a portion of a proximal-posterior bone of the femur; and   mounting the femoral prosthesis on the femur,   wherein the femoral prosthesis is mounted on the femur such that the distal articulating surface is approximately tangent to a cartilage surface on a lateral side of the knee, the distal articulating surface is approximately perpendicular to a mechanical axis of the femur, and the lateral posterior surface is approximately tangent to a posterior cartilage surface on the lateral side of the knee.   
     
     
         12 . The method of  claim 11 , wherein the portion of the proximal-posterior bone of the femur is a medial proximal-posterior bone. 
     
     
         13 . The method of  claim 11 , wherein the femoral prosthesis further includes a medial condyle with a proximal-posterior tip, and the portion of the proximal-posterior bone of the femur that is removed is removed to match the proximal-posterior tip of the femoral prosthesis. 
     
     
         14 . The method of  claim 11 , wherein the femoral prosthesis further includes:
 an internal non-articulating surface;   an external articulating surface including the distal articulating surface, a medial posterior surface having a first medial end and a second medial end, and the lateral posterior surface having a first lateral end and a second lateral end, wherein the first medial end and the first lateral end are connected to the distal articulating surface;   a medial condyle extending from the first medial end to the second medial end and formed between the medial posterior surface and the internal non-articulating surface; and   a lateral condyle extending from the first lateral end to the second lateral end and formed between the lateral posterior surface and the internal non-articulating surface.   
     
     
         15 . The method of  claim 14 , wherein a first height of the medial condyle measured from a line tangent to the distal articulating surface to the second medial end is less than a second height of the lateral condyle measured from the line tangent to the distal articulating surface to the second lateral end. 
     
     
         16 . The method of  claim 15 , wherein the medial condyle further includes a proximal-posterior tip, the proximal-posterior tip is shifted inwards relative to a proximal-posterior portion of the femur. 
     
     
         17 . The method of  claim 15 , wherein the medial condyle further includes a proximal-posterior tip, the proximal-posterior tip having a smooth rounded profile matching geometry of the native femur. 
     
     
         18 . The method of  claim 15 , wherein the femoral prosthesis comprises a material selected from the group consisting of thermoplastic polymers, thermoset polymers, titanium, titanium alloy, tantalum, cobalt chrome alloy, stainless steel, and ceramics. 
     
     
         19 . The method of  claim 15 , wherein a difference in height between the medial condyle and the lateral condyle is within the range of about 0.5 millimeters to about 5 millimeters. 
     
     
         20 . The method of  claim 15 , wherein a radius of a proximal-posterior portion of the medial condyle is less than a radius of a proximal-posterior portion of the lateral condyle.