Mechanical failure modes in total knee replacement.

In an attempt to define failure modes, a study of 39 knees which failed mechanically has been carried out. In 7 cases failure occurred on the femoral side and in 32 on the tibial side. There was fracture of one femoral component. All femoral loosenings and/or sinkage occurred in malaligned components. Two main tibial failure modes were noted, lateral subluxation of the tibia on the femur leading to loosening and sinkage of the tibial component. Release of popliteus prevents lateral subluxation. Correct component alignment and the use of a large area tibial component resting on the cortices should decrease the incidence of tibial sinkage.