Prosthetic knee joint with improved patellar component tracking

Claim 1

A knee joint prosthesis including a tibial component adapted to be secured to the proximal tibia and having a spaced pair of tibial condylar bearing portions; a patellar component adapted to be secured to the patella and having a patellar bearing surface; and a femoral component adapted to be secured to the distal femur and having an anterior plate portion adapted to contact said patellar bearing surface with the prosthetic knee joint at full extension, spaced femoral lateral and medial condylar bearing portions adapted for mutual articulation with said tibial condylar bearing portions, and a web portion joining said two femoral condylar bearing portions at their anterior ends and along at least a part of their respective lengths from said anterior ends, said femoral condylar bearing portions having generally convex bearing surfaces and said web portion having a concave bearing surface, said anterior plate portion, femoral condylar bearing surfaces and web portion bearing surface defining together a continuous track to cooperate with said patellar bearing surface and guide the patellar component during flexion of the prosthetic knee joint from a fully extended state to a fully flexed state, and with the bearing surface of said lateral femoral condylar bearing portion, as viewed in transverse cross sections through said femoral bearing portion along said track, being steeply sloped towards said web portion over at least the innermost one-third of the width of the bearing portion so as to substantially deepen the lateral wall of said track guiding the patellar component and thereby reduce the tension on the quadriceps mechanism at high degrees of flexion and substantially increase the maximum level of flexion achievable with the prosthetic knee joint, the generally convex bearing surface of said lateral femoral condylar bearing portion exhibiting, as viewed in transverse cross sections through said bearing portion along said track, a smooth continuous line consisting essentially of, from outside to inside, a first arcuate outer segment having a radius of curvature R 1 , which runs into a second segment, which runs in turn into a third arcuate inner segment having a radius of curvature R 2 , said second segment being relatively flat, R 2 being at least about 2.5 times R 1 , and the arc length of the third segment being at least about as long as the length of said second segment.