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

The 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.

A 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.

A 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%.

The 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.