Tibial component wear in total knee replacement.

Polyethylene wear is currently 1 of the major problems of total knee replacement. Evaluation of a large number of revised tibial components showed 3 wear patterns. Symmetrical central and symmetrical posterior wear are rare. Asymmetric wear beginning at the posteromedial part of the tibial plateau is the common pattern. The first step in the main wear process is cold flow of the polyethylene of the posteromedial part of the tibial plateau. The horizontal axis of rotation becomes fixed by this plastic deformation, and wear of the posteromedial part of the plateau then ensues. The vertical axis of rotation also becomes trapped, resulting in external rotation of the tibia on the femur leading to maltracking, exacerbating the wear and leading to an increased volume of wear debris, which eventually leads to chronic synovitis and osteolysis. Wear is more pronounced in the thinner units. Absence of a cruciate gap seems to prevent the initial cold flow and thus minimizes wear.