Association between the Critical Shoulder Angle and Rotator Cuff Tears in Japan

Distinct anatomic variants of the scapula such as the critical shoulder angle (CSA) were found to be associated with rotator cuff tears (RCTs), but it is unclear whether the CSA is a risk factor in Japanese. Here we sought to determine whether the CSA is associated with RCTs in a Japanese population, and whether the CSA is a more useful parameter than the conventionally used parameters. Our RCT group and non-RCT group each consisted of 54 consecutive cases. We compared the groups’ values of CSA, the acromion index (AI), and the lateral acromion angle (LAA) obtained by X-ray imaging. Receiver operating characteristic (ROC) analyses were performed to determine cutoff values and the area under the curve (AUC), and to assess the odds ratio. The means of the CSA and the AI in the RCT group were significantly larger (36.3° vs. 33.7°, 0.74 vs 0.68), but the LAA did not show a significant between-group difference. The AUCs for the CSA and AI were 0.678 and 0.658, the cutoff values were 35.0° and 0.72, and the odds ratios were 3.1 and 2.5, respectively. In conclusion, the CSA was a strong risk factor compared to the AI and LAA for rotator cuff tears.