Enhanced polyethylene implants: have we been there before?

Ultra-high molecular weight polyethylene (UHMWPE) has been used as a bearing surface in total hip arthroplasty for nearly 40 years. Early failures have been attributed to gamma irradiation in air sterilization, poor implant design, and high patient activity. Currently available implants address the problems of gamma irradiation in air by using sterilization methods that avoid oxidative degradation. Previous efforts to modify UHMWPE, including carbon reinforcement, hot isostatic pressure, and heat pressing, have not resulted in improved clinical performance. More recently, highly cross-linked UHMWPEs have been developed that markedly reduced wear in hip simulators. However, cross-linking also reduces the mechanical properties, including fatigue crack propagation resistance. Although early clinical results with highly cross-linked UHMWPE are favorable, longer follow-up will be necessary to determine whether the results of in vitro testing accurately reflect long-term in vivo behavior.