In vitro assessment of proximal polyethylene contact surface areas and stresses in mobile bearing knees.

Wear of the polyethylene (PE) insert in total knee arthroplasty remains a significant problem. The generation of biologically active wear particles may ultimately affect implant longevity through osteolysis or premature/catastrophic PE failure. The rate and pattern of wear is influenced by many factors, including component geometry and individual loading conditions, which determine the contact surface area and kinematics of the reconstructed knee. Contact areas and stresses at the proximal femoral-PE insert interface and distal PE-tibial interface contact surface areas were measured in nine mobile bearing total knee designs at 0, 30, 60, 90 and 110 degrees of flexion at 3600 N (5 x body weight) using a standardized test method. Proximal and, to a lesser degree, distal interface contact area footprints decreased significantly with increasing flexion angle based on the conformity of the designs, resulting in a corresponding increase in the mean and peak stresses.