Purpose: Metal-on-metal (MOM) bearing surfaces release ions locally and into the systemic circulation. This elevation raises concern about the long term effects of elevated metal ions. The goal of the present study was to monitor serum cobalt (Co) and chromium (Cr) levels in patients after MOM resurfacing hip arthroplasty with the Cormet 2000 prosthesis. We present here pilot data on Co and Cr levels in patients with bilateral versus unilateral hip resurfacing devices.

Method: We prospectively collected patient characteristics, outcome, and serum samples from device implanted subjects at 6 months, 1, 2, and 3 years following surgery. Unilateral patients had one implant during the entire course of follow-up and bilateral patients were included after the second implant surgery was performed. Serum Co/Cr levels were determined using high-resolution inductively coupled plasma mass spectrometry. Students t-test was used to compare ion levels in two groups based on the number of resurfacing implants (bilateral versus unilateral).

Results: 41 unilateral and 9 bilateral subjects were enrolled and followed for serum Co and Cr levels. In general, Co/Cr levels were increased at all time points when compared to control levels in both groups. Bilateral subjects had average serum levels concentrations significantly higher than those observed for unilateral cases (Co: 5.99 vs 2.56 μg/L (p=0.0001); Cr: 6.66 vs 3.60 (p=0.0009).

Conclusion: Elevated serum Co/Cr levels were observed at all time points following implantation in both groups and serum levels were nearly 2 times higher in the bilateral group. Based on these preliminary findings, patients undergoing bilateral total hip resurfacing arthroplasty may need to be monitored more closely than those patients receiving unilateral devices. In addition, these bilateral cases may be at a greater risk of ion level toxicities than the unilateral population.

Introduction: Metal-on-metal (MOM) hip resurfacing releases ions locally and into the systemic circulation, raising concern for potential long term complications of elevated trace metals. This study was designed to monitor serum cobalt (Co) and chromium (Cr) levels in patients after MOM resurfacing hip arthroplasty with the Cormet 2000 prosthesis and to compare detected levels with those previously reported for hip resurfacing prostheses.

Methods: We prospectively followed patients receiving the Cormet 2000 device. Serum samples were collected at 6 months, 1, 2, and 3 years following surgery. Pre-operative controls were obtained from subjects without implants. Serum Co/Cr levels were determined using high-resolution inductively coupled plasma mass spectrometry. ANOVA was used to compare ion levels in each group. Statistical significance was set at p< 0.05.

Results: 40 subjects (25 male) were followed. Average age was 51 years (33.7–66.1). Median preoperative Co/ Cr levels were 0.27 microg/L (0.087–0.601) and 0.19 (0.014–0.576), respectively. Co/Cr levels were significantly increased at all time points when compared to preoperative levels (p< 0.001). Peak Co and Cr levels were observed at 1 year (3.26 and 4.42, respectively). At three years, the median Co and Cr levels had dropped to 2.08 and 3.55, respectively, but this was not statistically significant.

Conclusion: Elevated serum Co/Cr levels were observed at all time points following implantation. Continued elevations at three years were observed; however, the levels appear to be trending down suggestive of a “wear-in” period. Long term elevations of Co/Cr levels are concerning and will require additional studies to assess long term health risks of these levels in this population.