Serum Metal Ion Levels in Modular Dual Mobility Liners After Total Hip Arthroplasty: A Comparison by Years and Implant Manufacturers.

Abstract

Modular dual-mobility (DM) liners are commonly used in total hip arthroplasty (THA) to decrease the risk of instability. However, there are concerns about accelerated wear, corrosion, and metal ion release in modular DM constructs. This study aimed to investigate serum metal ion levels over time after THA and evaluate any differences between implant manufacturers. This retrospective study enrolled 165 patients who underwent THA with a modular DM liner. Serum cobalt (Co), chromium (Cr), and zirconium (Zr) levels were assessed via a one-time blood draw. Patients were grouped into time cohorts of one to 2, 2 to 5, 5 to 8, and 8+ years based on years since DM placement. The primary outcome was serum Co, Cr, and Zr levels. Reference values of < 1.5 mcg/L for Co and < 1.2 mcg/L for Cr were considered within normal limits. Median Co and Cr levels were 0.3 (range, 0.2 to 7) and 0.3 (range, 0 to 3.1) mcg/L, respectively. There were 13 patients (7.9%) who had abnormally elevated metal ion levels; 10 received implant A (13%), two received implant B (4%), and one received implant C (3%). The Zr levels were undetectable in all patients. Median Co levels (0.4 mcg/L) were higher within 2 years of DM implantation and had a greater range of values than other time periods (P < 0.001). Successive time periods displayed a decreased range of Co values over time. There was a greater range of Co levels within 2 years of implantation, which reduced in variability over successive time periods. Although this could suggest an initial "settling-in" period of DM constructs, sequential blood draws from individual patients over time are needed to confirm such trends. Longitudinal tracking of metal-ion levels over time in modular DM implants is recommended.