Abstract: A prothesis tibial bearing of thermoplastic material has a planar surface which engages the mating planar surface of a second prothesis component such as the tibial platform. The typically metal platform edge wipes across the inner surface region of the bearing causing deformation of the bearing surface. This deformation causes stress magnification in the bearing at the platform edge region. The edge region of the platform planar surface is tapered to provide a gradual curved ramp between a relatively small corner radius at the platform edge and the platform planar surface, the tapered region being tangential to the edge radius and to the platform planar surface. The stress concentration increase at the edge region of the bearing is reduced at the platform edge region to below 100% and preferably to about 25% of the stress value between the bearing and the platform in the region interior the platform edge.

Abstract: Joint endoprostheses, disclosed in the context of a total knee prosthesis, incorporate a first element for rigid connection to a first bone, the first element having an articulating surface; a second element for rigid connection to a second bone, the second element having a bearing surface which engages the articulating surface; wherein the engagement of the articulation surface with the bearing surface at any degree of relative rotation therebetween is reflected by a substantially constant contact configuration, the relative rotation of the device being accompanied by displacement of the bones toward and away from each other.