Polyethylene Wear and Osteolysis

Wear particles and debris occur in the contact surfaces between implants and/or bone. Wear debris derived from ultra-high molecular weight polyethylene (UHMWPE) and metals of various size ranging from submicron to several microns are phagocytosed by monocytes and macrophages, inducing foreign body granulomas and causing osteolysis and loosening around the artificial hip joints. According to size, wear products can be classified into bulk (solids), large (particles), moderate (fine particles), small (microparticles), and very small (metal ion/metal ion complexes). They can form pseudotumors around the prosthesis or cause necrotic destruction of soft tissues. The synergistic effect of pressure loading and the foreign body granulomatous reaction widens the access space between the bone tissue and implant (Access Theory). Recently, wear resistance has been achieved by crosslinking treatment with gamma rays or electron beams, remelting of UHMWPE, and containing vitamin E, which can suppress the internal oxidation of UHMWPE. Surface treatment of UHMWPE with a 2-methacryloyloxyethyl phosphorylcholine polymer can reduce the coefficient of friction on sliding surfaces, thus leading decrease in wear particles. In clinical practice, computed tomography is useful imaging for findings of periprosthetic biological reactions including osteolysis, implant laxity, and soft-tissue evaluation. Reconstruction of loosed implants should be considered depending on the extent of the massive bone defect and fixation technique used for the specialized implants with auto- and allogeneic bone grafting.