A Randomized Controlled Trial of a Conventional Versus Modular Dual-Mobility Bearing: Are Serum Metal Levels a Concern?

Abstract

The primary purpose of this randomized controlled trial was to evaluate serum metal levels in patients after total hip arthroplasty (THA) with a conventional compared with a modular dual-mobility bearing. The secondary aim was to compare patient-reported outcome measure (PROM) scores between the 2 cohorts. Patients undergoing primary THA for osteoarthritis were randomized to receive either a modular dual-mobility or conventional polyethylene bearing. All patients received the same titanium acetabular and femoral components and a ceramic femoral head. Serum cobalt and chromium levels were measured preoperatively and annually at 1 through 5 years postoperatively. A total of 53 patients were enrolled. The 2 cohorts did not differ significantly in terms of demographics. In the conventional-bearing cohort, 76% of the patients were White and 24% were Black, African American; 48% of the patients were male and 52% were female. In the dual-mobility cohort, 86% of the patients were White and 14% were Black, African American; 79% of the patients were male and 21% were female. Forty-one patients who were randomized to a modular dual-mobility (n = 24) or conventional (n = 17) bearing and had a minimum follow-up of 2 years underwent serum metal analysis. No differences in serum cobalt levels (mean, 0.14 ng/mL [range, 0.075 to 0.29 ng/mL] versus 0.21 ng/mL [range, 0.075 to 0.57 ng/mL]; p = 0.22) or chromium levels (mean, 0.14 ng/mL [range, 0.05 to 0.50 ng/mL] versus 0.12 ng/mL [range, 0.05 to 0.35 ng/mL]; p = 0.65) were identified between the modular dual-mobility and conventional cohorts, respectively, at the 2-year postoperative time point. There were no significant differences in serum cobalt or chromium levels at 1 and 2 years postoperatively in patients who received a ceramic femoral head and this specific dual-mobility bearing compared with a ceramic head and a conventional acetabular component. While modest expected elevations in postoperative relative to preoperative serum cobalt and chromium levels were observed in the dual-mobility group, in no case did the cobalt level exceed the laboratory reference range or the threshold of 1 ng/mL that has been associated with adverse local tissue reactions due to mechanically assisted crevice corrosion. Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.