Ceramic bearing surfaces.

Despite more than 25 years of clinical experience with ceramic materials as bearing surfaces, their role in modern joint replacement surgery remains to be clearly defined. The two primary materials are alumina and zirconia. The application of these materials is primarily as a femoral head bearing surface against polyethylene, but alumina also is used as a femoral head and an acetabulum to provide a polyethylene-free bearing surface. Important issues that must be clarified for these materials to gain wide acceptance are the material properties, wear rates against polyethylene and alumina, the biologic response to ceramic wear debris, and cost in relation to indications. The bulk materials are biocompatible, hard, wettable, high-strength, and can yield good surface finishes. Linear polyethylene wear against alumina heads is reported to be as much as a factor of 5 to 10 lower than metal versus polyethylene. Thus, the ceramic femoral head may be a good choice for the younger patient in whom it seems necessary to use a larger head for stability reasons with a polyethylene cup. Ceramic-on-ceramic wear rates are in the range of 0.003 mm/year, a factor of 10 less than the lowest polyethylene wear rates. These costly materials are limited in head and neck sizes because of statistical variation in strength that can lead to fracture. Occasional reports of high alumina-on-alumina wear have appeared. Many of the problems of the past have been design, manufacture, or application related, and have been improved or eliminated. Proper clinical technique in the use of ceramic femoral heads is crucial to prevent fracture. The materials hold high promise and should continue to be used so that additional experience can help define the clinical indications for components made of these materials.