Patent ID: 8808387

Claim:
A prosthesis for replacement of at least part of a knee joint comprising: a tibial articular component having a medial compartment defining a medial tibial articular surface, a lateral compartment defining a lateral tibial articular surface, and a first formation between the medial compartment and the lateral compartment; and a femoral articular component having a medial condylar articular surface for bearing on the medial tibial articular surface, a lateral condylar articular surface for bearing on the lateral tibial articular surface, and a second formation between the lateral condylar articular surface and the medial condylar articular surface for bearing on the first formation of the tibial articular component; wherein at least one of the first and second formations is partially symmetric and partially asymmetric such that the interaction of the first and second formations during articulation of the femoral articular component relative to the tibial articular component does not bias any rotation of the tibial articular component relative to the femoral articular component at relative orientations corresponding to knee flexion of less than 60° of knee flexion and the interaction of the femoral and tibial formations during articulation of the femoral articular component relative to the tibial articular component biases internal rotation of the tibial articular component relative to the femoral articular component at relative orientations corresponding to knee flexion of greater than 110° of knee flexion, and wherein the first formation is a groove longitudinally oriented in a sagittal direction and the second formation is a ridge and wherein the ridge is positioned to slide in the groove in the anterior-posterior direction.