Wear of ultra-high molecular weight polyethylene moving along a circular path in a hip simulator

Abstract Multi-directional motion at the ball–socket interface of a hip replacement joint has been discovered as a fundamental feature that determines the magnitude of wear for ultra-high molecular weight polyethylene (UHMWPE). The present study considers the wear of UHMWPE moving along a circular path with a uniform angular change rate of the velocity vector defined by the curvature of the sliding circle. Experiments were conducted on a hip joint simulator with a biaxial rocking motion that results in a circular sliding path at the polar region of the acetabular cup that experiences the highest contact stresses and wear. The radius of sliding circle, r , depends solely on the radius of femoral ball, R , and the biaxial rocking angle, α , such that r =sin  α . For non-crosslinked UHMWPE, the wear rate as defined by volume loss per unit sliding distance (mm 3 /mm) is directly proportional to the curvature of sliding circle (1/ r ) while the wear rate as defined by volume loss per cycle (mm 3 /cycle) is independent of the radius of sliding circle.