Is Ultrasound As Useful As Metal Artifact Reduction Sequence Magnetic Resonance Imaging in Longitudinal Surveillance of Metal-on-Metal Hip Arthroplasty Patients?

BACKGROUND: Current guidelines recommend longitudinal monitoring of at-risk metal-on-metal (MoM) arthroplasty patients with cross-sectional imaging such as metal artifact reduction sequence (MARS) magnetic resonance imaging (MRI) or ultrasound. During follow-up evaluations, the clinical focus is on the relative interval changes in symptoms, radiographs, laboratory tests, and cross-sectional imaging modalities. Although MRI has the capacity for the detection of adverse local soft tissue reactions (ALTRs), the potential disadvantages of MARS MRI include the obscuration of periprosthetic tissues by metal artifacts and the cost. The aim of this study was to evaluate the diagnostic accuracy of ultrasound in comparison with MARS MRI in detecting ALTR in MoM patients during consecutive follow-up.

METHODS: Thirty-five MoM patients (42 hips) were recruited prospectively to evaluate the sensitivity and specificity of the ultrasound for detecting ALTR in relation to MARS MRI during 2 longitudinal follow-up scans. The agreement between ultrasound and MARS MRI in ALTR grade, size, and size change was calculated.

RESULTS: At the initial evaluation and at the subsequent follow-up, ultrasound had a sensitivity of 81% and 86% and a specificity of 92% and 88%, respectively. At the follow-up evaluations, ultrasound was able to detect the "change" in the lesions size with -0.3 cm(2) average bias from the MARS MRI with higher agreement (k = 0.85) with MARS MRI compared to the initial evaluation in detecting any "change" in ALTR size or grade.

CONCLUSION: Ultrasound detected the interval change in the ALTR size and grade with higher accuracy and higher agreement with MARS MRI compared with the initial evaluation, suggesting ultrasound is a valid and useful.