Human Motion and Its Relevance to Wear and Failure in Total Knee Arthroplasty

The natural human knee is a complex and heavily loaded joint. The articulation must transmit large forces while allowing significant motion at the same time. Typically, the knee undergoes a six-degree-of-freedom movement including both rolling and sliding (1). For functional reasons, freedom of movement and stability are important characteristics for the artificial knee joint as well. Technically, the latter are demanding requirements because of mixed kinematics and the high stresses placed on the articulation (2). As a result, wear and fatigue of the tibial polyethylene bearing are common failure criteria.