The Prevalence of Positive Findings on Metal Artifact Reduction Sequence Magnetic Resonance Imaging in Metal-on-Metal Total Hip Arthroplasty.

BACKGROUND: We sought to assess the prevalence of soft tissue changes seen on magnetic resonance imaging (MRI) after metal-on-metal (MOM) total hip arthroplasty (THA) and determine if the presence of pseudotumors was associated with metal ion levels, acetabular cup position, outcomes scores, and femoral head size.

METHODS: After receiving an institutional review board exemption for secondary data analysis, we performed a cross-sectional study identifying 55 patients (55 hips) that underwent primary THA with a MOM articulation and had subsequent MRI imaging between February 2013 and February 2014 at a single academic medical center.

RESULTS: Twenty-four patients (44%) had no evidence of pseudotumors, 27 (49%) had type I pseudotumors, and 4 (7%) were classified as having type II pseudotumors. The presence and severity of pseudotumors were associated with higher serum chromium levels (P = .043). Neither acetabular inclination nor acetabular version was associated with the presence of pseudotumors, the severity of pseudotumors, or elevated serum metal ion levels (all P > .05). Increased metal ion levels were associated with lower Harris Hip Score and higher Harris Hip Score pain subscores (all P < .05).

CONCLUSION: In conclusion, pseudotumors on metal artifact reduction sequencing MRI may be present in both symptomatic and asymptomatic MOM THAs. Surgeons should therefore exercise caution in placing too much emphasis on isolated studies such as cross-sectional imaging. Instead, a structured approach to evaluation of MOM arthroplasty should be followed.