Abstract
Background and objectives
Local bone-related adverse events occur more frequently following metal-on metal hip resurfacing (MOMHR) versus convention total hip arthroplasty (THA). High local tissue levels of cobalt and chromium may contribute to impaired bone health, however the systemic effects on bone of exposure to elevated metal levels after MOMHR are unknown.
Methods
In this cross-sectional study we compared whole body bone mineral density (WB-BMD) and biochemical markers of bone turnover in 31 healthy male subjects at a mean of 8 years after MOMHR versus 31 individually age and time since surgery matched male subjects after conventional THA. All subjects had well-functioning prostheses and were in good self-reported health as assessed by Oxford Hip Score and EQ-5D questionnaire. WB-BMD was measured by dual energy x-ray absorptiometry and adjusted for pre-morbid osteoporosis risk factors using the FRAX tool, and for the presence of the metal prostheses using identical exclusion regions. Bone turnover markers were measured on fasting morning serum or 24hr urine collection by electro-chemiluminescent assay. Cobalt and chromium were measured by ICP-MS.
Results
The subject pairs were similar for all matching criteria (P>0.05, all comparisons). Cobalt and chromium were elevated in the MOMHR versus THA group (P<0.05, all comparisons). WB-BMD was 7% higher in the MOMHR versus THA subjects (1.05 versus 0.98 g/cm2, P= 0.002). Bone formation, measured by serum osteocalcin, was 17% lower in the MOMHR versus THA subjects (18.2 versus 21.1ng/mL, P= 0.02) and osteoclast number measured by TRAP 5b, was 23% lower (3.4 versus 3.9U/L, P= 0.008). Systemic levels of bone formation and resorption markers were inversely correlated with systemic cobalt, but not chromium levels (Spearman, P<0.05).
Conclusion
Subjects 8 years after MOMHR versus THA have higher WB-BMD and lower bone turnover measured by some markers, and marker activity inversely correlate to systemic cobalt levels. These data suggest that this metal has a systemic suppressive effect on bone turnover. The difference in BMD may be due to a reduction in age-related bone loss since surgery, although the measured BMD might also be due, in part, to diffuse metal deposition within the skeleton.
