Sensitivity and Specificity of Metal Ion Level in Predicting Adverse Local Tissue Reactions Due to Head-Neck Taper Corrosion in Primary Metal-on-Polyethylene Total Hip Arthroplasty

Background: There is increasing concern regarding the occurrence of adverse local tissue reactions (ALTRs) in metal-on-polyethylene (MoP) total hip arthroplasty (THA) patients due to mechanically assisted crevice corrosion at the head-neck modular taper junction. The utility of metal ion levels in evaluating MoP patients with head-neck taper has not been fully characterized. This study aimed to investigate the sensitivity and specificity of serum metal ions as a predictor of ALTR in MoP THA patients. Methods: A total of 62 MoP THA patients in 2 cohorts were investigated: (1) ALTR on metal artifact reduction sequence magnetic resonance imaging (n = 43) and (2) without ALTR on metal artifact reduction sequence magnetic resonance imaging (n = 19). Receiver-operating characteristic curve was constructed to determine the sensitivity and specificity using different metal ion thresholds and the optimal metal ion cutoff values. Results: The presence of ALTR was associated with significantly higher cobalt (8.9 ng/mL vs 0.3 ng/mL, P <.001), chromium (2.26 ng/mL vs 0.21 ng/mL, P <.001), and Co/Cr ratio (5.9 vs 2.0, P <.001). The sensitivity and specificity for cobalt (1 ng/mL) was 95% and 94% and for Co/Cr ratio (2) was 83% and 72%, respectively. Conclusions: Although metal ion levels alone should not be relied on as the sole parameter to determine revision surgery, serum cobalt level of >1 ng/mL (1 ppb) and Co/Cr ratio >2 thresholds provide evidence-based practical information for surgeons when interpreting metal ion levels in MoP THA patients for clinically relevant head-neck taper corrosion.