| Summary: | The last decade saw a resurgence in the use of large diameter metal on metal (MoM) hip arthroplasties. Some of these devices have reported an unacceptably high failure rate secondary to the development of soft tissue lesions. Multiple sources have reported that patients with total hip replacement (THRs) with taper junction experience greater failure rates. Using the facilities of a national explant retrieval unit, a prospective study was conducted to investigate the relationships between the wear of MoM devices, the corresponding blood, serum and synovial fluid cobalt (Co) and chromium (Cr) concentrations, and the host aseptic lymphocyte dominated vasculitis associated lesion (ALVAL) response and soft tissue damage as noted during revision surgery. Investigation of the role of blood metal ions in identifying poorly performing bearing surfaces revealed linear regression analysis demonstrated a powerful relationship between total volumetric wear rates and blood Co and Cr concentrations, with R2 values greater than 85% (p<0.001). Examining the source of metal debris and its relationship to blood/joint fluid metal ions and periprosthetic tissue metal particle sizes revealed greater wear rates were associated with larger particle sizes in excised tissues (p<0.001). Greater source contribution of wear debris from the taper junction was associated with significantly lower synovial fluid Cr concentrations and smaller particle sizes (p<0.001). Examining the soft tissue damage and ALVAL response revealed, the extent of soft tissue injury observed at revision surgery was more strongly associated with the presence of fluid and the ALVAL grade than the synovial fluid concentrations of Co and Cr or total volumetric wear. The higher grade ALVAL was associated with increasing age and joint fluid Co concentrations (p<0.001). While adverse reactions occurred more frequently in the presence of abnormally wearing devices, soft tissue injury does not appear to be mediated by a direct toxic effect of metal.
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