Cross-sectional area of the labrum: role in the diagnosis of anterior acetabular labral tears.

Objective: To investigate the utility of ultrasound cross-sectional area (CSA) measurements for diagnosing acetabular labral (AL) tears.

Methods: The study included qualitative/quantitative ultrasound examinations of 55 hips in 52 patients with a presumed diagnosis of AL tear and 56 hips in 28 healthy volunteers. MR arthrography examinations were available only for the patients and were reviewed for the presence of AL thickening and tear.

Results: The CSA of the anterior labrum was significantly larger in patients with an AL tear on MR arthrography than those in healthy volunteers (P < 0.01). The CSA cut-off value in determining labral thickening that maximises accuracy was 34.7 mm(2), and sensitivity, specificity and accuracy were 86.7%, 74.1% and 77.5%. Direct signs of AL tear on ultrasound had sensitivity, specificity and accuracy of 34.9%, 91.7% and 47.3%. The CSA cut-off value that maximises the accuracy of the AL tear was 40.6 mm(2), and sensitivity, specificity and accuracy were 58.1%, 91.2% and 78.4%.

Conclusions: Ultrasound detects the thickened labrum frequently observed in MR arthrography studies, especially in patients with dysplastic hips. Although specificity of the method of detecting AL tears is high, sensitivity is low, with an overlap between subjects with AL tear and controls.

Key Points: • Labral degeneration is frequent in dysplastic hips • Thickened labra are frequently observed on MR arthrograms • Labral thickening can be depicted by quantitative ultrasound measurements • The sensitivity is low with overlap between subjects with AL tear and controls.