Good sensitivity and specificity of ultrasound for detecting pseudotumors in 83 failed metal-on-metal hip replacements

Abstract

Background and purpose — Ultrasound is used for imaging of pseudotumors associated with metal-on-metal (MoM) hips. Ultrasound has been compared with magnetic resonance imaging, but to date there have been no studies comparing ultrasound findings and revision findings.

Methods — We evaluated the sensitivity and specificity of preoperative ultrasound for detecting pseudotumors in 82 patients with MoM hip replacement (82 hips). Ultrasound examinations were performed by 1 of 3 musculoskeletal radiologists, and pseudotumors seen by ultrasound were retrospectively classified as fluid-filled, mixed-type, or solid. Findings at revision surgery were retrieved from surgical notes and graded according to the same system as used for ultrasound findings.

Results — Ultrasound had a sensitivity of 83% (95% CI: 63–93) and a specificity of 92% (CI: 82–96) for detecting trochanteric region pseudotumors, and a sensitivity of 79% (CI: 62–89) and a specificity of 94% (CI: 83–98) for detecting iliopsoas-region pseudotumors. Type misclassification of pseudotumors found at revision occurred in 8 of 23 hips in the trochanteric region and in 19 of 33 hips in the iliopsoas region.

Interpretation — Despite the discrepancy in type classification between ultrasound and revision findings, the presence of pseudotumors was predicted well with ultrasound in our cohort of failed MoM hip replacements.

OL: study design, literature search, data collection and analysis, interpretation of data and statistics, writing and revision of the manuscript, and final approval. PE, AR, JP, TP, and AE: study design, interpretation of data and statistics, writing and revision of the manuscript, and final approval.

We thank Ella Lehto for maintaining our study database, and Heini Huhtala for assistance with statistical analyses. The study was supported by the competitive research funds of Pirkanmaa Hospital District, Tampere, Finland (grant 9N044, representing government funding). The source of funding had no role at any stage of this study.

JP has a consultant contract with Zimmer. TP has received research funding from Smith and Nephew. No commercial companies were involved in planning of the study, data collection, analysis and interpretation of data, or writing of the manuscript.