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Arthroscopic surgery of the hip is being increasingly used to diagnose and treat various abnormalities, including acetabular labral tears. Magnetic resonance arthrography has been suggested as the imaging test of choice for the evaluation of the acetabular labrum. There is substantial variability in the previously reported accuracy of magnetic resonance arthrography for diagnosing labral lesions. Interobserver reliability has not been established previously. The purpose of this study was to establish the interobserver reliability and the validity of magnetic resonance arthrography for detecting lesions of the acetabular labrum in a retrospective case series.Two radiologists independently assessed the acetabular labrum on magnetic resonance arthrograms of ninety-five hips in ninety-three patients who underwent hip arthroscopy for a suspected acetabular labral lesion. Magnetic resonance arthrography findings were compared with the gold standard, which was defined as the assessment of the labrum during the hip arthroscopy.At arthroscopy, ninety-one labral lesions were identified in the ninety-five hips. The interobserver reliability of detecting labral lesions with magnetic resonance arthrography was fair (kappa = 0.268). Magnetic resonance arthrography, as interpreted by observers A and B, showed a sensitivity of 86% and 86%, specificity of 75% and 50%, negative predictive value of 19% and 13%, and positive predictive value of 99% and 98%, respectively.Because of its limited reliability and the high prevalence of labral lesions, magnetic resonance arthrography provides a limited complementary benefit in the detection of labral lesions in patients with a high clinical suspicion of labral pathology. When there is a high clinical suspicion of a labral lesion, magnetic resonance arthrography has a poor negative predictive value and cannot be used to rule out a labral lesion. Physicians should critically consider whether the findings on a magnetic resonance arthrogram will alter the treatment strategy for an individual patient with a clinical suspicion of labral pathology.