How do serum cobalt and chromium levels change after metal-on-metal hip resurfacing?

We prospectively monitored changes in serum cobalt and chromium levels after a new generation metal-on-metal hip resurfacing and the affect on renal function. Levels were measured using inductively coupled plasma mass spectrometry and atomic absorption spectrometry, preoperatively then sequentially at 3, 6, 9, 12, and 24 months. For serum cobalt, there was an initial increase to a peak level at 6 months, followed by a gradual decline during the next 15 months. A similar trend was observed in serum chromium, although the peak level occurred slightly later, at 9 months. There was no adverse affect on renal function during the 2-year study period. All implants were functioning well, with no radiographic evidence of loosening. These levels will continue to be monitored to establish when minimum metal ion levels are reached.