Encouraging results and new implant developments have allowed total hip replacement to be performed in increasingly younger and more active patients. In young patients, however, outcomes are not comparable to those seen in older patients. The inflammatory reaction to polyethylene wear particles is one of the main causes of aseptic loosening and subsequent revision surgery and can limit the longevity of an arthroplasty in young and active patients. The wear resistance of polyethylene has been improved by cross-linking; however, greater degrees of cross-linking are associated with progressive decreases in other material properties, which theoretically increase the risk of component failure from very high or localized stresses. Ceramic femoral heads have been associated with lower in vivo polyethylene wear rates, which have been variable and up to 50% lower than with metallic heads. Metal-on-metal bearings have been reintroduced with improved materials, design, and manufacturing, although theoretical concerns remain regarding long-term exposure to metal particles and ions. Improved ceramic-on-ceramic bearings also are available and have the lowest wear rates. They offer a very small risk of in vivo fracture; however, they are the most expensive bearing option and wear rate is more sensitive to implant position. Long-term clinical studies are needed to show a reduction in revision surgery associated with the use of this current generation of bearings. The use of any of these bearings has specific benefits and risks that should be considered on a patient-by-patient basis.





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