[Joint biomechanics and design of modern knee prostheses--time for revised thinking!]

This review article summarises new knowledge about knee kinematics and induces a new discussion about the design of total knee arthroplasty (TKA) components.

According to these new observations, knee flexion is not linked to femoral rollback but to a rotational movement between tibia and femur. The axis of this rotation is situated in the medial compartment of the knee when an intact anterior craciate ligament is present and not centrally through the tibial spines. In case of ACL insufficiency, such as that following TKA, the center of rotation shifts into the lateral compartment. Furthermore, the form of the posterior femoral condyle is not elliptical but round.

Rotational movements between femoral component and tibial baseplate with the polyethylene-inlay have to be possible. One needs an asymmetric surface of the polyethylene-inlay, because different movements occur in the medial compartment than in the lateral compartment. The option to construct the posterior femoral condyle with a single radius allows a high congruency with the articulating inlay. The surgeon should let the new findings influence his choice of a TKA system. A closer analysis of modern prosthetic designs with either fixed or mobile bearings reveals that a few systems have already incorporated some of the new kinematic aspects of the knee.