Abstract: BACKGROUND: As the largest and only anterior rotator cuff muscle in the rotator cuff muscle group, the subscapularis muscle is often neglected for its injury, and the local injury of the subscapular muscle is still difficult to diagnose. In recent years, studies have found that the coracohumeral distance and coracoid overlap distance were used as predictors of subscapularis muscle injury.
OBJECTIVE: To investigate the relationship between the coracohumeral distance, coracoid overlap distance and the difference between the coracohumeral distance of the patient’s bilateral shoulder joint and subscapularis injury, and to evaluate the diagnostic efficacy of each parameter on subscapularis injury.
METHODS: Preoperative clinical and imaging data of patients with degenerative rotator cuff injury from February 2021 to June 2022 were retrospectively collected, and patients were divided into the group with rotator cuff injury combined with subscapularis tear (subscapularis tear group, 28 patients) and the group with rotator cuff injury without subscapularis tear (control group, 56 patients) based on intraoperative arthroscopic findings. The CT data of the enrolled patients were imported into Mimics software in DICOM format. The scapula and proximal humerus of the patients were reconstructed; the measurement points were determined to establish the measurement plane; the coracohumeral distance and coracoid overlap distance of the patients were measured in 3-matic software. The differences in parameters between the two groups of patients and bilateral differences within the groups were compared, and receiver operating characteristic curve analysis was performed for each parameter to determine the area under the curve and the optimal cut-off value for each parameter.
RESULTS AND CONCLUSION: (1) Coracohumeral distance among groups: (7.00±0.87) mm in the subscapularis tear group and (9.08±1.02) mm in the control group. Coracohumeral distance in the subscapularis tear group was significantly smaller than that in the control group (P < 0.01). Coracoid overlap distance among groups: (21.05±1.98) mm in the subscapularis tear group and (19.46±1.55) mm in the control group. Coracoid overlap distance in the subscapularis tear group was significantly larger than that in the control group (P < 0.01). (2) Difference in coracohumeral distance between the two groups: The coracohumeral distance of the affected side of the subscapularis tear group (7.00±0.87) mm was significantly smaller than that of the healthy side (9.26±0.87) mm, and the difference was statistically significant (P < 0.01). (3) The receiver operating characteristic analysis: the areas under the curve for the difference in coracohumeral distance, coracoid overlap distance, and bilateral coracohumeral distance were 0.884, 0.729, and 0.905, respectively; the best cut-off values were 7.65 mm, 20.2 mm, and 1.15 mm, respectively. (4) It is concluded that the coracohumeral distance, coracoid overlap distance, and bilateral coracohumeral distance difference are all related to subscapularis injury, and all can be used as predictors of subscapularis injury, with coracohumeral distance difference having the highest predictive efficacy, and the three measured parameters can provide some reference values in preoperative clinical diagnosis.

Key words: rotator cuff injury, subscapularis injury, coracohumeral distance, coracoid overlap distance, three-dimensional reconstruction, scapula, coronoid process