Serum Metal Ions in Contemporary Monoblock and Modular Dual Mobility Articulations

BACKGROUND: Questions exist about the release of cobalt and chromium ions from dual mobility (DM) cups. Modular implants, with potential backside wear between the cobalt-chromium liner and titanium cup, are of particular concern. This study compares the metal ion profile of patients with contemporary monoblock and modular DM articulations from two commonly used designs. METHODS: Cobalt and chromium serum levels were measured one year after surgery in a prospective cohort of patients undergoing total hip arthroplasty with a DM construct. Ion levels were detected above 1 μg/L. Clinical and surgical data were correlated with the ion levels for analysis. RESULTS: Overall, 29% of the patients had levels above 1 μg/L of either ion. More patients with modular cups had detectable ions than patients with monoblock cups (39% vs 20%, P = .05). Cobalt was more commonly detected in the monoblock group, and chromium was more commonly detected in the modular group (P = .05). There were no differences in the actual ion levels between the groups (1.35 μg/L vs 1.64 μg/L, P = .44, for cobalt and 1.35 μg/L vs 1.31 μg/L, P = .77, for chromium). No patient underwent revision during the follow-up period. CONCLUSIONS: We found similar cobalt and chromium levels in patients with monoblock and modular DM cups. More patients in the modular group had detectable ions. Cobalt was more frequently detected in the monoblock group. These results suggest that both implants are performing well in the short term, but further follow-up is needed to determine whether the differences found are of clinical significance.