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.

Metal-on-metal (MOM) hip resurfacing devices are known to release metal ions locally and into the systemic circulation. Previous studies suggest that larger prosthetic head size will correlate to reduced wear properties and may result in lower systemic release of metal ions. This project assessed the effect of femoral head size on serum cobalt (Co) and chromium (Cr) levels in subjects after unilateral hip resurfacing with the Cormet 2000 prosthesis.

We prospectively collected patient characteristics, outcome, and serum samples from device implanted subjects at six months, one, two, and three years following surgery. 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 femoral head size.

Thirty-five subjects (twenty male) were followed. Co/Cr levels were increased at all time points when compared to control levels. A significant negative correlation was observed between Co and Cr levels and femoral head size. Co/Cr levels in subjects with larger femoral heads were significantly lower when compared to those implanted with smaller heads (Co, −35.8%; Cr, −33.0%). This correlated with significantly higher Co/Cr levels in females versus males, with females receiving significantly smaller heads on average.

Elevated serum Co/Cr levels were observed at all time points following implantation and in females and in subjects with femoral heads.