The medial-ridge sign as an indicator of anterior glenoid bone loss

BackgroundThe goal of this study was to investigate the incidence of a medial bony ridge at the scapular neck in patients with recurrent anterior shoulder instability and analyze its reliability in identifying anterior glenoid rim bone loss.MethodsA total of 109 shoulders in 105 consecutive patients underwent primary surgical stabilization for recurrent anterior shoulder instability with preoperative 2-dimensional and 3-dimensional computed tomography (CT) evaluation. The CT images of each affected shoulder were analyzed for the extent of anterior glenoid bone loss and the presence of a “medial-ridge sign.” The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the medial-ridge sign were calculated for different sizes of glenoid rim defects.ResultsA positive medial-ridge sign was detected in 77.1% of the shoulders. The sensitivity of the medial-ridge sign ranged from 81.6% (95% confidence interval [CI], 73.0%-87.9%) for defects greater than 0% to 100% (95% CI, 82.4%-100%) for defects ≥20%. The PPV of the medial-ridge sign decreased from 100% for defects >0% to 11.9% for defects ≥25%. The specificity of the medial-ridge sign decreased from 100% (95% CI, 61.0-100%) for defects >0%, to 25.3% (95% CI, 17.7%-34.6%) for defects ≥25%. The NPV of the medial-ridge sign increased from 24.0% for defects >0% to 100% for defects >20%.ConclusionThe medial-ridge sign represents a CT-based radiologic sign with high sensitivity and NPV for identification of significant anterior glenoid rim defects in case of recurrent anterior shoulder instability.