Long-term follow-up and metal ion trend of patients with metal-on-metal total hip arthroplasty.

PURPOSE: Long-term studies are required to support the use of metal-on-metal (MoM) bearings in total hip arthroplasty (THA) given the concern about systemic metal ion release and reports of adverse local soft tissue reactions. The purpose of this study was to report the seven to 13-year clinical, radiographic, and metal ion results in patients following MoM THA.

METHODS: We studied 163 prostheses after second-generation MoM THA between July 1997 and November 2003. Cobalt and chromium metal ions were collected using whole and analysed by inductively-coupled plasma-mass spectrometry.

RESULTS: The mean follow-up was 8.87 years (range, 7-13 years). Four hips (2.5 %) were revised. The Kaplan-Meier survivorship was 91.3 % for revision for all causes, and 97.5 % when excluding the hips revised for a manufacturer's defect. Median whole blood cobalt levels peaked at a value of 2.87 μg/L at four years (p < 0.0001 vs. pre-operative) and subsequently decreased to 2.0 μg/L after nine years (p = 0.002 vs. four years). Median chromium levels maximally increased up to 0.75 μg/L after five years (p < 0.0001 vs. pre-operative) and tended to decrease thereafter to values of 0.56 μg/L after seven years.

CONCLUSIONS: This seven to 13-year follow-up study indicates that the clinical and radiological results following MoM THA are satisfactory with low revision rates. Cobalt and chromium ion levels peaked at four and five years, respectively, and gradually decreased thereafter.