Knee prostheses

Abstract

A total knee prosthesis comprises a femoral component and a patellar component. The femoral component has a patellar flange into which is built a twist or roller coaster configuration. The patellar component has an off-set dome with respective lateral and medial facets. The configuration of the patellar flange resists forces from a medial to a lateral direction, whilst the lateral and medial facets of the patellar component are respectively shaped to allow area contact and line contact respectively with the femoral component. Also disclosed is a device for intra-operative checking of patellar tracking to allow correct insertion of the femoral and patellar components.

1 .- 33 . (canceled) 
   
   
       34 . A total knee prosthesis comprising a femoral component and a patellar component, the femoral component having lateral and medial condyles which are curved in both a transverse and a sagittal plane, an open intercondylar area between said condyles, a patellar flange, and a patellar groove extending from said open intercondylar area to a free end of the patellar flange, and the patellar component having an articular surface formed with an off-set domed region and providing a lateral facet and a medial facet, wherein the lateral facet is curved in both a transverse and a sagittal plane to allow area contact with the femoral component when in use and the medial facet is curved in a transverse plane to allow line contact with the femoral component when in use. 
   
   
       35 . The prosthesis according to  claim 34  wherein the patellar flange of the femoral component has an articular surface contacting the patellar component, in use, which is for a distance expanding inwardly from the free end of the patellar flange configured to resist forces, in use, from a medial to a lateral direction. 
   
   
       36 . The prosthesis as claimed in  claim 34 , wherein on full extension, the domed region has point contact with the femoral component. 
   
   
       37 . The prosthesis as claimed in  claim 34 , wherein in slight flexion up to 45° the domed region makes the line contact in a floor of the patellar groove of the femoral component. 
   
   
       38 . The prosthesis as claimed in  claim 34 , wherein above 45° degrees of flexion the domed region makes no contact in the intercondylar box area and on the lateral side load is taken through the lateral facet with area contact on the lateral femoral condyle of the femoral component. 
   
   
       39 . The prosthesis as claimed in  claim 38 , wherein on the medial side, the medial facet has a cross-section effecting line contact on the medial femoral condyle. 
   
   
       40 . The prosthesis according to  claim 34 , wherein a twist or roller coaster configuration is built into the femoral component to resist forces from a medial to a lateral direction. 
   
   
       41 . The prosthesis according to  claim 40 , wherein the degree of twist decreases away from said free end. 
   
   
       42 . The prosthesis according to  claim 41 , wherein the twist is terminated at a spacing from said free end of the patellar flange lying within the open intercondylar area. 
   
   
       43 . The prosthesis according to  claim 34 , wherein the open intercondylar area is enclosed by an intercondylar box. 
   
   
       44 . The prosthesis according to  claim 34 , wherein the domed region is offset medially. 
   
   
       45 . The prosthesis according to  claim 44 , wherein the off-set is a selected value of one of 3 mm, 5 mm or 7 mm. 
   
   
       46 . The prosthesis according to  claim 34 , wherein the patellar component is in one piece. 
   
   
       47 . The prosthesis according to  claim 34 , wherein the patellar component is of plastics material. 
   
   
       48 . The prosthesis according to  claim 34 , wherein the patellar component has a non-articular surface. 
   
   
       49 . The prosthesis according to  claim 48 , wherein the non-articular surface has fixation means.