(a) Postoperative and (b) 11.31 year follow-up radiographs of a 28 mm cobalt chrome head on UHMWPE Reflection polyethylene liner. Linear penetration of the head was measured to be 5.581 mm, with observed femoral osteolysis in Gruen zones 1 and 7 (white arrowheads). (c) Postoperative and (d) 10.53 year follow-up radiographs of a 28 mm cobalt chrome head on XLPE Reflection polyethylene liner. Linear penetration of the head was measured to be 0.335 mm, with no observed osteolysis. UHMWPE: ultra-high molecular weight polyethylene, XLPE: highly cross-linked polyethylene.