Evaluation of the reliability and relationship with physical examination of a novel ultrasound index, the “concave sign,” for symptomatic hip labral tears

This study aimed to evaluate the reliability of a novel ultrasound index, the “concave sign,” obtained by ultrasound observation, and to evaluate its association with physical examination. Forty patients diagnosed with symptomatic hip labral tears who were undergoing conservative treatment were enrolled. Ultrasonography was used to observe the concave deformity (concave sign) of the joint capsule on the labral surface during gluteus minimus contraction. The reliability of the presence of the concave sign was examined using the κ coefficient, and the association between the concave sign and the anterior impingement test (AIT) as well as the flexion–abduction–external rotation (FABER) test was analyzed using Fisher's exact test. The intra-rater reliability for detecting the concave sign was κ = 0.81, and the inter-rater reliability was κ = 0.90. Among those with a positive concave sign, 95.7% were positive for the AIT and 87.0% were positive for the FABER test; a significant association was observed for both tests ( p < 0.01 and p < 0.05, respectively). This investigation indicated that the concave sign is a reliable ultrasound index for detecting adhesion-like pathology of the hip labrum and joint capsule and demonstrated its clinical utility as an adjunct to physical examination. • Reliability of the “concave sign” on ultrasound in hip labral tears was assessed. • Association of the concave sign with hip pain also was evaluated. • The concave sign was found to be highly reliable. • The concave sign correlated significantly with the AIT and FABER test. • The concave sign detects adhesion-like pathology in the labrum and capsule.