0827 - Multidirectional Wear in Fully-congruent Acetabular Implants of Enhanced and Conventional Polyethylene

Introduction: Polyethylene wear has been implicated in osteolysis and implant loosening. Most clinical studies use migration of the femoral head as an index of acetabular polyethylene wear, with the assumption that wear occurs in a single direction. A recent retrieval study, however, demonstrated evidence of multiple wear (deformation) vectors in acetabular components in which the liner was not fully-congruent with metal backing (1). Multiple vectors apparently are not the result of cup motion in vivo; other possible mechanisms include impingement, un-even head roughness, the gait cycle, impact loading after head separation from the cup in vivo (2), and polyethylene creep with changing contact areas related to non-congruent designs. The purpose of this study is to test the latter hypothesis by evaluating the direction(s) of wear in a fully-congruent acetabular cup design. A secondary goal of the study is to compare the magnitude of wear in retrieved “enhanced” polyethylene (Hylamer, DePuy, Inc) liners compared with conventional polyethylene (Enduron) from the same manufacturer.