High Performance Knee Prostheses

Abstract

Knee prostheses featuring components that more faithfully replicate the structure and function of the human knee joint in order to provide, among other benefits: greater flexion of the knee in a more natural way by promoting or at least accommodating internal tibial rotation in a controlled way, replication of the natural screw home mechanism, and controlled articulation of the tibia and femur respective to each other in a more natural way. In a preferred embodiment, such prostheses include an insert component disposed between a femoral component and a tibial component, the insert component preferably featuring among other things a reversely contoured postereolateral bearing surface that helps impart internal rotation to the tibia as the knee flexes. Other surfaces can also be specially shaped to achieve similar results, preferably using iterative automated techniques that allow testing and iterative design taking into account a manageable set of major forces acting on the knee during normal functioning, together with information that is known about natural knee joint kinetics and kinematics.

1 . A prosthetic implant, comprising:
 a tibial insert having a medial bearing surface and a lateral bearing surface; and   a femoral component having a medial condylar surface and a lateral condylar surface, the medial condylar surface being configured to contact the medial bearing surface and the lateral condylar surface being configured to contact the lateral bearing surface:   (i) such that the femoral and tibial components can move in flexion and extension with respect to one another;   (ii) such that moving the femoral and tibial components in flexion from substantially 0° to substantially 130° moves a contact point between the lateral bearing surface and the lateral condylar surface posteriorly from an anterior portion of the lateral bearing surface to a posterior portion of the lateral bearing surface; and   (iii) such that moving the femoral and tibial components in flexion from substantially 0° to substantially 130° permits an internal rotation of the tibial insert relative to the femoral component.   
     
     
         2 . The prosthetic implant of  claim 1 , wherein the medial condylar surface is configured to contact the medial bearing surface such that as the knee flexes from 0° and 130°, a contact point between the medial bearing surface and the medial condylar surface moves posteriorly from an anterior portion of the medial bearing surface to a posterior portion of the medial bearing surface. 
     
     
         3 . The prosthetic implant of  claim 1 , wherein the lateral condylar surface moves along a convex arc of the lateral bearing surface. 
     
     
         4 . The prosthetic implant of  claim 3 , wherein the lateral bearing surface comprises a curved generally concave portion, the curved generally concave portion sweeps laterally from the anterior portion toward a middle portion and sweeps medially from the middle portion toward the posterior portion. 
     
     
         5 . The prosthetic implant of  claim 1 , wherein when moving the femoral and tibial components in flexion greater than 130°, the lateral and medial condylar surfaces move only posteriorly relative to the tibial insert. 
     
     
         6 . The prosthetic implant of  claim 1 , wherein the tibia insert internally rotates at least substantially 8° relative to the femoral component at substantially 130° of flexion and greater flexion angles. 
     
     
         7 . The prosthetic implant of  claim 1 , wherein the medial condylar surface of the femoral component is greater in size than the lateral condylar surface of the femoral component, and the tibial insert is thicker in at least some areas that cooperate with the lateral condylar surface of the femoral component than in corresponding areas that cooperate with the medial condylar surface of the femoral component. 
     
     
         8 . The prosthetic implant of  claim 1 , wherein the femoral component further includes a cam having an asymmetrical shape such that the lateral side of the cam is larger than the medial side and being configured to cooperate with a posterior surface of the tibial insert, the cam configured to impart internal rotation to the tibial insert relative to the femoral component at angles of flexion between the tibial insert and the femoral component of 50° or greater.