[Association of increased greater tubercle angle and critical shoulder angle with rotator cuff tears]

The greater tuberosity angle (GTA) and critical shoulder angle (CSA) are commonly referred to as radiographic markers which were used to described morphology of the greater tuberosity and acromion respectively. At present, most international studies focus on the correlation between the above two parameters and rotator cuff tears (RCTs), and their diagnostic value and risk assessment. This study attempts to find out the trend of GTA and CSA changes and risk threshold of RCTs, as well as the protective factors and risk factors.

In this study, 130 individuals from May 2019 to December 2020 were recruited. According to Southern California Orthopedic Institute (SCOI) classification, the individuals were divided into four groups retrospectively: Group A, negative control group; Group B, partial tears (articular side); Group C, partial tears (bursal side); Group D, full-thickness tears. GTA and CSA were measured respectively on true anteroposterior position X-ray of shoulder with arm in neutral rotation and performed by the same trained technician team in single-blind. The correlations between RCTs and relevant factors were analyzed.

According to the area under the receiver operating characteristic curve (AUC), GTA and CSA of RCTs (Groups B, C and D) were 0.736 and 0.673 with 95% confidence interval (CI), the cut-off value of GTA and CSA of RCTs were 70.5° and 39.5° respectively. Comparing with the control group, RCTs groups had significant statistical differences in age and body mass index (BMI) (P < 0.05), especially the full-thickness RCTs (Group D), which was older than Groups A, B and C (P < 0.05, cut-off value: 56.5 years old) and shorter than Groups A and B (P < 0.05, cut-off value: 1.58 m). Analyzed from scatter plot and regression analysis, there was no linear correlation between GTA and CSA. There were no significant differences in gender, dominant shoulders and smoking between the RCTs groups and the control group (P>0.05).

Larger GTA (>70.5°) and CSA (>39.5°) would be highly predictive in diagnosing RCTs without linear correlation, and GTA has a higher diagnostic value in contrast. Subacromial impingement and shoulder degeneration occurred before RCTs. Patients with age >56.5 years and height < 1.58 m were more likely to develop disease of full-thickness RCTs and no statistic differences in weight and BMI. Gender, dominant shoulder and smoking were neither risk factors nor protective factors.