Serum Metal Ion Levels in Modular Dual Mobility Acetabular Components: A Systematic Review

Background: Dual mobility (DM) constructs effectively reduce the risk of dislocation in revision and high risk primary total hip arthroplasty. However, modular DM designs require the use of a cobalt-chrome liner against a titanium cup which may induce corrosion, metal ions release, and associated biologic response. The purpose of this systematic review study was to collect all reported cases of serum metal ions after DM in the literature and ask the following questions: 1) what is the overall rate of significantly elevated Cobalt and Chromium metal ions and how do these levels change over time? 2) Does femoral head material composition influence serum metal ion levels? and 3) were there any atypical lymphocytic associated lesions after modular DM that required revision surgery?

Methods: A systematic review was performed according to PRISMA guidelines. In addition to patient demographics, information specific to the performance of the DM implant were recorded including: cobalt and chromium serum ion levels and all reported timepoints, the material composition of the femoral head, all revision and reoperations and any failure related to corrosion of the DM bearing. A significant elevation in cobalt or chromium was defined as >1.0 or >1.6 mcg/L.

Results: 248 modular DM THAs were analyzed. The cumulative mean cobalt and chromium levels for all included studies was 0.47mcg/L and 0.53mcg/L, respectively. At final follow-up 13 patients (5.2%) had elevated cobalt ion levels and 4 patients (1.6%) had elevated chromium ion levels. Femoral head material composition trended towards but did not significantly increase serum ion levels. Ceramic heads had elevated cobalt and chromium ions in 4/135 (3%) of patients compared to metal heads which had elevated cobalt ions in 9/113 (8%) and elevated chromium ions in 0/113 (0%), (p = 0.09). There were no reoperations or revisions for metal related reactions at final follow-up (mean 27.4 months).

Conclusion: In this systematic review including 248 modular DM THAs, elevated serum cobalt ions were present in 5.2% of patients at a mean follow-up of 27.4 months. While a trend towards increased Cobalt serum ions with the use of cobalt chrome femoral heads, femoral head composition was not significantly associated with increased serum metal ion levels. At final follow-up, metal ion levels appear to decrease in the majority of patients between 1 and 2 years and no patient was revised for metal ion related complications. Continued serum metal ion surveillance is recommended to ensure the safety of DM constructs in THA with longer term follow-up.