Diagnostic accuracy of preoperative magnetic resonance arthrography for detecting midsubstance capsular tears: Irregular outline sign.

Abstract

Traumatic anterior shoulder instability is caused by functional and structural failure of the inferior glenohumeral ligament-labrum complex. One such cause is midsubstance capsular tear, which is a rare condition with a prevalence of 1.5 %-4.0 %. It is crucial to obtain accurate preoperative imaging of a midsubstance capsular tear because of the high skill level required for surgical treatment. However, reproducible and reliable radiological features for the diagnosis of midsubstance capsular tear have not been identified, and although the distorted shape of the magnetic resonance arthrography is reportedly a sign of midsubstance capsular tear, its reproducibility and reliability have not been adequately demonstrated. The present study investigated the diagnostic accuracy of the Irregular Outline (IO) sign on magnetic resonance arthrography for diagnosing midsubstance capsular tear. This retrospective study included 204 shoulders with traumatic anterior shoulder instability after excluding patients with previous surgeries, fractures, or poor-quality magnetic resonance arthrography images. Two examiners evaluated the magnetic resonance arthrography images for the IO sign, and the presence of midsubstance capsular tear was confirmed via arthroscopic records. Midsubstance capsular tear was identified in 12 of 204 shoulders (5.9 %). The IO sign demonstrated high diagnostic accuracy with a sensitivity of 85.4 %, specificity of 94.9 %, positive predictive value of 51.8 %, and negative predictive value of 99.1 %. The inter-rater and intra-rater reliabilities were high, with kappa coefficients above 0.8. The IO sign on magnetic resonance arthrography is a reliable indicator with high sensitivity and specificity for diagnosing midsubstance capsular tear. The accurate preoperative diagnosis of a midsubstance capsular tear can assist in planning appropriate surgical interventions, especially for shoulder surgeons with less experience. Further studies are needed to confirm these findings in larger populations and with standardized imaging equipment.