Systemic Metal Ion Exposure in Resurfacing Arthroplasty: A Prospective 10-Year Longitudinal Study

Introduction Modern metal-on-metal bearing resurfacings have been in use for nearly two decades. Local and systemic metal ion exposure continues to cause concern. We could not find a prospective metal ion study in such patients with a 10-year follow-up. This is the first ten year prospective study of metal ion levels in blood and their release in urine following hybrid fixed metal-on-metal surface arthroplasty. Methods Twenty six patients were included in an ongoing longitudinal metal ion study of patients with unilateral metal-on-metal hip resurfacings. Three of them were excluded due to subsequent contralateral resurfacing and one has relocated abroad. Cobalt and chromium levels were assessed in 12 hour urine collections before and periodically after operation (5 days to 10 years) using high resolution plasma mass spectrometry. Mean age at operation was 53 years and mean BMI 27.9. Results Hip function questionnaires at the 10-year review showed that the patients have well-functioning pain-free resurfacings (mean Oxford hip score 14.3). Metal ion results show median cobalt and chromium release at 10 years were 8.3 μg/24 hr and 4.35 μg/24 hr respectively. A statistically significant early peak 6 months to 1 year after operation is followed by a steady decrease over the following seven years although the reductions are not statistically significant. Discussion and Conclusion Elevated systemic metal ion exposure continues to cause concern in patients treated with metal-metal arthroplasties. Our results show that metal release in these bearings shows a reducing trend after an initial peak. The unknown significance of persistent metal ion elevation underlines the need for continued long-term monitoring.