Femoral Head Size Does Not Affect Ion Values in Metal-on-Metal Total Hips

Background Metal-on-metal articulations can release substantial amounts of particles containing cobalt and chromium into the surrounding milieu, causing concern for cellular toxicity and adverse local soft tissue reactions. The diameter of the femoral head has been one of the variables that inversely affects wear of metal-on-metal total hip arthroplasty (THA). The oxidative stress of increased metal ions can be measured with serum markers. It is still controversial if larger femoral head diameters decrease wear rates in patients with metal-on-metal THA and if the increased metal ions alter the body’s antioxidant status.

Questions/purposes We therefore (1) determined whole blood metal ions in patients with small (28 mm and 36 mm) and large (40 mm and 44 mm) diameter femoral heads; (2) measured oxidative stress markers (total antioxidants, nitrotyrosine, and peroxides); and (3) determined whether acetabular version or inclination influenced ion levels.

Methods One hundred four patients were retrospectively studied. We recorded Harris hip scores and UCLA activity scores. All patients were followed at 1 year.

Results The activity scores were similar in the two groups. There was no difference in metal ion levels or oxidative stress markers between patients with small- or large-diameter femoral heads. Acetabular inclination and anteversion had no effect on the metal ion levels.

Conclusions The data suggest there is no difference in ion values in patients with large or small metal-on-metal THA and the increased metal ions do not alter the oxidant status of the patient.

Level of Evidence Level III, retrospective comparative study. See Guidelines for Authors for a complete description of levels of evidence.