Metal ion levels and lymphocyte counts: ASR hip resurfacing prosthesis vs. standard THA: 2-year results from a randomized study

Background and purpose Wear particles from metal-on-metal arthroplasties are under suspicion for adverse effects both locally and systemically, and the DePuy ASR Hip Resurfacing System (RHA) has above-average failure rates. We compared lymphocyte counts in RHA and total hip arthroplasty (THA) and investigated whether cobalt and chromium ions affected the lymphocyte counts. Method In a randomized controlled trial, we followed 19 RHA patients and 19 THA patients. Lymphocyte subsets and chromium and cobalt ion concentrations were measured at baseline, at 8 weeks, at 6 months, and at 1 and 2 years. Results The T-lymphocyte counts for both implant types declined over the 2-year period. This decline was statistically significant for CD3 ⁺CD8 ⁺ in the THA group, with a regression coefficient of -0.04 × 10 ⁹cells/year (95% CI: -0.08 to -0.01). Regression analysis indicated a depressive effect of cobalt ions in particular on T-cells with 2-year whole-blood cobalt regression coefficients for CD3+ of -0.10 (95% CI: -0.16 to -0.04) × 10 ⁹ cells/parts per billion (ppb), for CD3+CD4+ of -0.06 (-0.09 to -0.03) × 10 ⁹ cells/ppb, and for CD3 ⁺CD8 ⁺ of -0.02 (-0.03 to -0.00) × 10 ⁹ cells/ppb. Interpretation Circulating T-lymphocyte levels may decline after surgery, regardless of implant type. Metal ions-particularly cobalt-may have a general depressive effect on T- and B-lymphocyte levels. Registered with ClinicalTrials.gov under NCT01113762.