A New Predictive Parameter for Rotator Cuff Tears: Acromial Incidence Angle.

Background: A significant statistical association of increased critical shoulder angle (CSA) with rotator cuff tear (RCT) has been demonstrated; however, the mean difference between RCT and control groups varies between approximately 1° and 3.5°, with a wide range of distribution of the CSA from 18° to 55°. It may be more predictive to evaluate the CSA in conjunction with parameters that evaluate the morphology of the acromion in the sagittal plane. Hypothesis: It was hypothesized that the acromial incidence angle (AIA), which can evaluate the position and orientation of the acromion in the sagittal plane, may be associated with RCT and that AIA, when evaluated together with the CSA, may provide a highly predictive measure of risk for RCT. Study Design: Cross-sectional study; Level of evidence, 3. Methods: The study included 117 patients who underwent arthroscopic repair for posterosuperior RCT and 117 patients as a control group. The CSA, AIA, glenoid inclination, glenoid version, and anterior acromial coverage were measured on magnetic resonance imaging. The groups were compared in terms of these parameters. Results: The mean CSA was significantly higher in the RCT group (35.7°± 5.3°) than in the control group (33.9°± 4.5°), with a sensitivity of 57.1% and a specificity of 61.3% ( Conclusion: The AIA predicted RCT with a sensitivity of 80.2% and a specificity of 83.9% for values >70°. In patients with a CSA of <35°, it predicted RCT, with a sensitivity of 85.6% and a specificity of 84.8% at values >72°. By evaluating the relationship between the acromion and the glenoid in the sagittal plane, the AIA, as a novel parameter, allows for the reevaluation of the risk in the patient group with a CSA of <35°, which is considered to be in the low-risk category in terms of RCT.