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

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 mum/year (range, 2.9-12.8 mum/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, 0.55-3.74mm(3) /year), which corresponds to a mean gravimetric wear rate of 16.9mg/year (range, 4.6-31.4mg/year). The mean clearance of 39.8 pm (range, 30-50 mum) 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. (C) 2002 Elsevier Science Ltd. All rights reserved.