Metal-metal bearing surfaces in hip arthroplasty.

There is no mystery regarding the allure of metal-metal bearings: high stability and low wear potential. The special risks associated with these bearings are coming into focus and include a macrophage response to excessive metal particles (metal reactivity) and a lymphocyte-dominated reaction (metal sensitivity). The most common presentation of an adverse local tissue reaction (ALTR) is persistent pain. The incidence of ALTR has not been completely defined, but the risk appears to be increased in resurfacing, in women, and in bilateral cases. The differential diagnosis includes septic and aseptic loosening, and the evaluation should include aspiration. The diagnosis is confirmed by histological examination.