Serum Metal Ion Concentrations After Unilateral vs Bilateral Large-Head Metal-on-Metal Primary Total Hip Arthroplasty

It is unknown if the presence of bilateral well-functioning large-head metal-on-metal (MOM) total hip arthroplasties (THAs) leads to higher serum metal ion concentrations than unilateral MOM THA. Elevated levels (chromium, 17 μg/L; cobalt, 19 μg/L) have been associated with poorly functioning MOM THA with metallosis. Fourteen patients having undergone bilateral and 25 patients having undergone unilateral large-head primary MOM THA were compared. Harris Hip Scores, University of California Los Angeles activity scores, radiographs, serum creatinine, and serum cobalt and chromium levels were obtained. Only cobalt ion levels were significantly higher in the bilateral group than in the unilateral group (1.8 μg/L vs 1.0 μg/L, P = .029). Comparatively, this magnitude is clinically rather low because ion levels did not approach those associated with metallosis in either group. We conclude that although patients with well-functioning bilateral MOM THA may have slightly higher cobalt levels, neither cobalt nor chromium levels approach those seen in poorly functioning MOM THA with metallosis.