Abstract
The purpose of this study was to prospectively measure serum cobalt and chromium ion levels in patients who had MITCH Resurfacing (Stryker) and to correlate these with acetabular component orientation (anteversion and inclination).
Twenty-seven patients were enrolled in the study. Serum ion levels were measured pre-operatively, six weeks, six months, twelve months and twenty-four months post-operatively. Axial CT scans of the pelvis were used to measure cup anteversion and plain radiographs used to measure cup inclination.
The median serum cobalt and chromium levels at one year were 14.5 nmol/l (range, 6 nmol/l to 59 nmol/l) and 36 nmol/l (range, 17nmol/l to 63 nmol/l) respectively. The median serum cobalt and chromium levels at two years were 16.5 nmol/l (range, 6 nmol/l to 75 nmol/l) and 37.5 nmol/l (range, 13 nmol/l to 109 nmol/l) respectively. The mean cup inclination was 43° (range, 30° to 60°). The mean cup anteversion was 19° (range, 1° to 47°). There was no clear correlation with cup position and serum ion levels. There was one outlier with slightly elevated chromium (109 nmol/l) in a female with a small head size.
All patients at all time points showed serum cobalt and chromium levels below the level indicating a high-risk implant (7 parts per billion or chromium >134 nmol/l and cobalt > 119 nmol/l). Our results show no clear relationship between cup position and serum metal ions in this group of patients with relatively well-positioned components
