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(9)cells/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