Metal Ion Levels Not Sufficient as a Screening Measure for Adverse Reactions in Metal-on-Metal Hip Arthroplasties

This study aims to assess the accuracy of metal ion analysis in the diagnosis of adverse reaction to metal debris (ARMD) in patients with metal-on-metal hip arthroplasties by comparing the cobalt and chromium levels in 57 patients (62 hips) to findings on metal artifact reduction magnetic resonance imaging (MRI). An ARMD was detected using MRI in 18 (29%) of the hips. Forty patients had cobalt levels less than 7 mu g/L, and 33 had chromium levels less than 7 mu g/L, but 8 of these had an ARMD on MRI and only minimal symptoms (Oxford Hip Score >= 44/48). The incidence of ARMD was significantly higher when chromium concentration was above 7 mu g/L (P=.02), but normal metal ion levels can be misleading and metal artifact reduction MRI imaging is advised in all patients.