The Double‐Circle System in the Greater Tuberosity: Using Radius to Predict Rotator Cuff Tear

OBJECTIVE: In this study we concerned on the morphological characteristics of the greater tuberosity of humerus and proposed the double‐circle radius ratio as a new predictor for the diagnosis of rotator cuff tears. METHODS: This was a retrospective study and patients who visited our hospital and were diagnosed with or without rotator cuff tears via magnetic resonance imaging from January 2018 to July 2021 were enrolled and classified into two groups respectively. In a standard anteroposterior view, the radius of the best‐fit circle of humeral head and the radius of the concentric circle passing through the most lateral edge of the greater tuberosity were measured in each shoulder. The ratio of these two radiuses was named as the double‐circle radius ratio. Angular parameters including the greater tuberosity angle and the critical shoulder angle were also measured in the anteroposterior view. Independent samples t tests and chi‐square tests were used to find significant differences between groups. Significant associations between those measured variables and demographic characteristics were analyzed with simple linear regression analysis. Receiver operating characteristic curves were pictured to determine applied cutoff values by using Youden index. Multivariable‐adjusted analysis for the occurrence of rotator cuff tears was carried out by using multiple logistic regression analysis. For all tests a p value of <0.05 was considered statistically significant. RESULTS: One hundred and twelve shoulders with rotator cuff tears and 42 shoulders without rotator cuff tears were included. The mean value of the double‐circle radius ratio was significantly larger in shoulders with rotator cuff tears (1.42 ± 0.09 vs. 1.30 ± 0.07, P = 0.000). With simple linear regression analysis, the radiuses of the humeral head and the greater tuberosity were significantly associated with heights and weights. In receiver operating characteristic curves, the largest area was found under the curve of the double‐circle radius ratio as 0.846 (95% CI, 0.781–0.911; P = 0.000) with an applied cutoff value as 1.38 (sensitivity, 70.5%; specificity, 88.1%). Multivariable‐adjusted analysis showed that a value of the double‐circle radius ratio >1.38 resulted in 11.252‐fold odds of developing rotator cuff tears (95% CI, 3.388–37.368; P = 0.000). CONCLUSION: The double‐circle radius ratio is significantly larger in patients with rotator cuff tears and could be regarded as an eligible predictor for rotator cuff tears.