To explore the association between critical shoulder angle (CSA) and calcific supraspinatus tendinitis (CST) in the rotator cuff, analyzing the possibility of CSA enlargement as a potential high-risk factor for CST from both clinical and imaging perspectives, and provide theoretical basis for early diagnosis and precise treatment of CST.

All CST patients who received treatment at the First Affiliated Hospital of the University of Science and Technology of China from June 2017 to January 2024 were included. The patients with no other shoulder joint diseases before surgery and undergoing arthroscopic shoulder surgery were enrolled in the CST group, while the patients with rotator cuff tears and history of shoulder surgery were excluded. An equal number of patients admitted to the hospital during the same period due to clavicle fractures were matched and included in the control group. The shoulder joint X-rays of all the patients before operation were extracted, and CSA was measured twice by the same researcher at one month interval. Independent sample t test was used to compare the CSA values of CST group and control group. The patients in CST group were divided into different subgroups according to CSA size, and the associations between visual analog scale (VAS) for shoulder pain and American Society of Shoulder and Elbow Surgeons (ASES), University of California shoulder score (UCLA) and other functional scoring systems scores before operation and at one year after operation were analyzed.

A total of 100 patients were enrolled, with 50 cases in the CST group and 50 cases in the control group available for analysis. The average CSA in CST group (39.6±3.7) ° was higher than that of the control group (34.5±1.5) ° (t=8.97, P<0.001). Patients with larger CSA in the CST group had higher pain scores and poorer functional scores before surgery (t=3.81, P<0.05). After surgery, the pain and functional scores in the CST group were improved, and there were no statistically significant differences in the pain and functional scores among the different CSA subgroups (all P>0.05). The proportion of typeⅢ acromion (hook type) in the CST group was 56% (28/50), while only 12% (6/50) in the control group, the difference was statistically significant (χ²=21.58, P<0.001). There was no statistically significant difference in VAS, ASES, and UCLA scores between the two groups after surgery (all P>0.05).There was no statistically significant difference in VAS, ASES, and UCLA scores (all P>0.05) between the patients whether underwent rotator cuff repair.

There is a correlation between CST and increased CSA, suggesting that increased CSA may be a high-risk factor for CST occurrence. Although CST patients with larger CSA may have poorer shoulder joint function before surgery, pain and functional scores after surgery could still show similar improvements as the small CSA patients.