Long-term results of the M(2)A-38-mm metal-on-metal articulation

BACKGROUND: Large-diameter head metal-on-metal (MoM) bearings in total hip arthroplasty (THA) are associated with increased whole blood levels of chromium (Cr) and cobalt (Co), adverse reactions to metal debris (ARMD) and poor survival rates. The prevalence of high metals concentrations, ARMD and the risk of revision surgery may vary significantly among different prostheses and long-term studies are few. This single-center study reports the long-term results of the 38-mm MoM bearing system. MATERIALS AND METHODS: Between 2003 and 2009, 80 patients received primary cementless THA using the large head metal-on-metal articulating surface M(2)A-38 cup (Biomet, Inc., Warsaw, IN, USA) at a single institution. Forty-five patients (53 hips) were retrospectively reviewed for a mean follow-up of 127 months. RESULTS: Two cups were revised. The cumulative implant survival rate was 98% at 10 years and 74% at 13 years. In the whole sample, the median Co and Cr concentrations were 4.8 µg/L (IQR 1.2–4.9 µg/L) and 2.5 µg/L (IQR 0.6–3.0 µg/L), respectively. The incidence of Co or Cr levels > 7 μg/L was 15.5% and the incidence of ARMD was 3.8%. Co and Cr levels showed no correlation with cup inclination, Harris Hip Score, or total Hip Disability and Osteoarthritis Outcome score. CONCLUSIONS: Our results confirm that the problems of release of metal ions with the possible increase of metal circulating levels and of adverse reactions may also occur in the long term with this brand of MoM large head, and that a structured follow-up program is mandatory. LEVELS OF EVIDENCE: Level 4.