Patent ID: 7922770
Filing Date: 2011-04-12
Classification: A61F

Abstract:
1. A total knee arthroplasty endoprosthesis comprising: a metallic femoral component including a spherical lateral condyle surface and a spherical medial condyle surface, the lateral condyle surface having a smaller radius than the medial condyle surface; a third condyle located between, posterior, and superior the medial condyle surface and the lateral condyle surface, and offset on the metallic femoral component in a direction of the medial condyle surface; a metallic tibial component including a central spigot; and a polyethylene insert including a bore that engages the central spigot, the polyethylene insert being rotatable about the central spigot of the metallic tibial component, the polyethylene insert having a medial cavity in conformity with a shape of the medial condyle surface and a lateral cavity in conformity with a shape of the lateral condyle surface, wherein the medial and lateral cavities are asymmetrical but equally deep, the polyethylene insert further comprises a third cavity in conformity with a shape of the third condyle, and located between, inferior, and posterior the medial cavity and the lateral cavity, and offset on the polyethylene insert in a direction of the medial cavity; wherein the medial and lateral condyle surfaces respectively engage the medial and lateral cavities at a medial bearing surface and a lateral bearing surface such as to be adapted to impose a geometrical relationship between an anatomic femoral axis and an anatomic tibial axis that approaches a physiological valgus of a knee joint; wherein at an advanced stage of flexion between the femoral component and the tibial component, the third condyle engages the third cavity at a central bearing surface that replaces the medial bearing surface and the lateral bearing surface, the central bearing surface being larger than either of the medial or lateral bearing surfaces; wherein the offset of the third condyle towards the medial condyle, assists rotation of the polyethylene insert with respect to the metallic tibial component about an axis defined by the bore and central spigot; wherein the central spigot of the metallic tibial component and the bore of the polyethylene insert are aliened on a mid-sagital plane of the total knee arthroplasty endoprosthesis wherein the third condyle is medially offset from the axis defined by the bore and central spigot, wherein the engagement of the central spigot with the bore prevents translational movement of the polyethylene insert, while permitting only rotational movement of the polyethylene insert about the axis defined by the bore and central spigot.