The exercise-related rise in plasma cobalt levels after metal-on-metal hip resurfacing arthroplasty 2008
M. Khan, MRCS, PhD Student, Clinical Research Fellow1; J.-H. Kuiper, PhD, Lecturer in Biomechanics1; and J. B. Richardson, MD, FRCS, Professor of Orthopaedics1
1 Institute of Orthopaedics The Robert Jones and Agnes Hunt Orthopaedic Hospital, Gobowen, Shropshire SY10 7AG, UK.
Wear of metal-on-metal bearings causes elevated levels of cobalt and chromium in blood and body fluids. Metal-on-metal bearings have two distinct wear phases. In the early phase, the wear rate is high. Later, it decreases and the bearing enters a steady-state phase. It is expected that as the wear rates decline, the level of cobalt detected in plasma will also decrease. We studied the baseline and exercise-related cobalt rise in 21 patients (13 men and eight women) with a mean age of 54 years (38 to 80) who had undergone successful hip resurfacing at a mean of 44 months (10 to 96) earlier. Our results showed that circulating baseline cobalt levels were not significantly correlated with the time since implantation (r = 0.08, p = 0.650). By contrast, the exercise-related cobalt rise was directly correlated with the inclination angle of the acetabular component (r = 0.47, p = 0.032) and inversely correlated with the time since implantation (r = –0.5, p = 0.020).