Retrieval study of uncemented metal–metal hip prostheses revised for early loosening

Abstract

A tribologic assessment was performed on 22 metal–metal hip prostheses from a single manufacturer, following removal for early aseptic loosening after a mean service life of 32 months (range, 12–59 months). The mean linear wear rate was 7.6 μm/year (range, 2.9–12.8 μm/year). This was below the rates previously observed in other modern metal–metal combinations. A novel contour analysis technique using a coordinate measuring machine showed the mean volumetric wear rate to be 2.02 mm 3/year (range, 0.55–3.74 mm 3/year), which corresponds to a mean gravimetric wear rate of 16.9 mg/year (range, 4.6–31.4 mg/year). The mean clearance of 39.8 μm (range, 30–50 μm) was within the optimal range for hard–hard bearing combinations. Evidence of abrasive, adhesive, and third-body wear was found on all bearing surfaces. The tribologic assessment did not indicate manufacturing defects as a cause of early loosening. Equally, third-body wear was too low to be considered a causative factor for early loosening.