Difference of Critical Shoulder Angle (CSA) According to Minimal Rotation: Can Minimal Rotation of the Scapula Be Allowed in the Evaluation of CSA?

BACKGROUND: Minimal rotation of the scapula may affect the measurement of critical shoulder angle (CSA). We investigated the difference in the CSA measured in minimal rotation between the patients with rotator cuff tear and those without non-rotator cuff tear and the CSA measurement error by comparing with computed tomography (CT). METHODS: We retrospectively reviewed patients with full-thickness rotator cuff tear and whose X-ray views correspond to Suter-Henninger classification type A1 and C1. The CSA values between the normal control group (without rotator cuff tear) and the rotator cuff tear group were compared according to A1 type and C1 type. In the rotator cuff tear group, we compared the CSA values measured by using X-ray and CT. RESULTS: A total of 238 patients (rotator cuff tear group, 139 patients; normal cuff group, 99 patients) were included in this study. The mean CSA of the rotator cuff tear group was 33.4° ± 3.5°, and that of the normal cuff group was 32.6° ± 3.9° (p = 0.085). On comparison of the CSA according to the Suter-Henninger classification type, the CSA values on the A1 type view and C1 type view were 32.7° ± 3.5° and 33.7° ± 3.5°, respectively, in the rotator cuff tear group and 30.5° ± 3.1° and 33.1 ± 3.9°, respectively, in the normal cuff group (p = 0.024 and p = 0.216, respectively). The mean CSA was 32.5° ± 3.1° in CT and 33.3° ± 3.2° in X-ray (p = 0.184). On comparison of the CSA according to the Suter-Henninger classification type, the CSA values on the A1 type view and C1 type view were 32.6° ± 3.6° and 32.5° ± 2.4°, respectively, in CT and 32.5° ± 3.5° and 34.2° ± 2.6°, respectively, in X-ray (p = 0.905 and p = 0.017, respectively). CONCLUSIONS: The X-ray view corresponding to Suter-Henninger classification type A1 or CT-reconstructed image can be used to reduce the measurement error and obtain reliable CSA values. The CSA measured on the X-ray view corresponding to Suter-Henninger classification type A1 may be related with rotator cuff tear.