Abstract
Comparisons of blood metal ion levels of cobalt and chromium (CoCr) between metal-on-metal total and resurfacing hip arthroplasties are limited. High levels of CoCr may result in long-term adverse biological effects. We compare metal ions levels between total and resurfacing implants.
70 patients (28 males and 42 females) had a total hip arthroplasty using the Birmingham (Smith & Nephew) modular femoral component and a variety of stems, articulating with the Birmingham resurfacing component. The average age was 65.5 (±6.8) years and an average follow-up of 6.0 (±2.2) years. 170 patients (145 male and 25 female had a Birmingham resurfacing arthroplasty with an average age of 54.7 (±9.9) years and an average follow-up of 5.9 (±3.0) years. CoCr levels were measured. Bivariate correlations and independent samples t-tests were applied to determine similarities and differences within and between groups.
Average ion levels in total arthroplasty patients were: Co 114.17 (±94.01) nmol/L (range 2–414); and Cr 75.12 (±68.45) nmol/L (range 10–312). Average levels in hip resurfacing arthroplasty were: Co 55.98 (±79.5) nmol/L (range 7–505); and Cr 70.77 (±87.41) nmol/L (range 5–751). Both total and resurfacing groups showed significant correlations (p<0.01) between Co and Cr levels. A significant difference was observed between the total and resurfacing group Co levels (p<0.0001). No significant difference was shown between group Cr levels (p>0.672).
The average total hip replacement CoCr levels were higher than the hip resurfacing levels. While the overall activity level may be higher in the resurfacing group, possibly the incidence of stop/start frequency may be higher in the total hip replacement group.
Hip resurfacing arthroplasty average CoCr levels are lower than those of total hip replacement patients. Associations between Co and Cr metal ion levels are shown within each group. Co levels differ significantly between groups where Cr does not. Long-term follow-up of CoCr levels are required.
