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Two alternative bearings for total hip arthroplasty: more data are needed.

In this issue of the Journal of the American Academy of Orthopaedic Surgeons, two articles presented in the Perspectives on Modern Orthopaedics series focus on the use of ceramic-on-ceramic and metal-onmetal alternative bearing surfaces for total hip arthroplasty. Total joint arthroplasties are now being performed in patients who are younger and more active, and the hope is that new alternative bearings, such as highly cross-linked polyethylene (XLPE), ceramic-onceramic, and metal-on-metal, will provide the durability and reduced wear rates that are necessary in this patient population. In their article titled “Ceramic Materials as Bearing Surfaces for Total Hip Arthroplasty,” D’Antonio and Sutton review the development of ceramic bearings, the clinical results, and the complications specific to this bearing surface. The authors are quite enthusiastic about the potential advantages with respect to wear rates with ceramic-on-ceramic bearings. Dr. D’Antonio has been one of the leading proponents of the use of ceramic bearings in the United States, and he has reported in a prospective study excellent results with one particular implant with midterm follow-up. However, based on the data available today, I would disagree with the authors’ assertion that ceramic-on-ceramic is the optimal bearing surface for young and active patients. Although total hip arthroplasties with an alumina ceramic bearing had superior survivorship compared with a metal head with a standard polyethylene liner, these liners are rarely used today. Randomized trials comparing ceramic articulations with XLPE and metal-on-metal bearing surfaces are necessary. D’Antonio and Sutton point out the disadvantages of the use of ceramic bearings, including ceramic head fracture, fewer prosthetic head and neck options, and the risk of squeaking. Ceramic head fracture are less frequent with modern heads, and the availability of Biolox delta (CeramTec AG, Plochingen, Germany) will provide larger head options, which will enhance the stability of these implants. However, it is the squeaking associated with these implants that has caught the attention of the public and is of significant concern to surgeons. The incidence of squeaking is variable (up to 7%), and its etiology has not been identified. In addition, the presence of squeaking confirms that ceramic-on-ceramic bearings are less tolerant of variations in component position than are other bearing surfaces, which is an important consideration when choosing a bearing surface. Although wear rates may be reduced in young and active patients treated with ceramic-on-ceramic total hips, until the squeaking issue is resolved, their use will be limited. However, the combination of a large ceramic head mated with a highly XLPE liner is an attractive option that deserves further study. In their article titled “Metal-onmetal Bearing Surfaces,” Jacobs et al provide a detailed and balanced review of the potential impact on clinical outcomes of the tribology and metal ion release associated with metal-on-metal bearing surfaces. The authors deJay R. Lieberman, MD Deputy Editor