Surgical variables influence metal ion levels after hip resurfacing

Metal-on-metal bearings in surface arthroplasty are associated with prolonged periods of elevated ion circulation. However, there exists some controversy regarding the effect of different surgical variables on the concentration of metal ions in whole blood of patients after hip resurfacing.

We sought to confirm which clinical and radiographic parameters are associated with elevated levels of cobalt, chromium, and molybdenum after unilateral metal-on-metal surface arthroplasty.

We retrospectively reviewed 91 patients with a minimum followup of 24 months (mean, 37 months; range, 24-55 months). The clinical variables consisted of age, gender, preoperative severity of osteoarthritis, component size, and functional outcome measures using the Harris hip score and UCLA activity score. The radiographic parameters included acetabular inclination and version as well as femoral component alignment from both the anteroposterior and lateral radiographs.

A smaller femoral head diameter was associated with larger levels of cobalt and chromium. We observed a negative correlation between ion levels and the Harris hip score or UCLA score. A larger acetabular inclination showed a direct relationship with the concentration of metal ions. Severity of preoperative osteoarthritis, acetabular version, femoral stem-shaft and valgus angle, and anterior orientation of the femoral component had no effect on the circulating metal ion levels.

The data suggest a smaller implant diameter, larger cup inclination, and lower postoperative functional scores are associated with increased cobalt and chromium levels after metal-on-metal hip resurfacing.