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

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 (mm3/mm) is directly proportional to the curvature of sliding circle (1/r) while the wear rate as defined by volume loss per cycle (mm3/cycle) is independent of the radius of sliding circle.