Objective To evaluate the role of rotator interval (RI) detection in Frozen shoulder (FS) patients by retrospectively analyzing the gray-scale and Doppler ultrasound findings. Method Thirty-five patients with frozen shoulder who underwent ultrasound examination and were clinically confirmed and thirty-seven non-frozen shoulder patients with shoulder discomfort in our hospital from June 2017 to December 2020 were retrospectively included. The patients with frozen shoulder were further divided into early group (≤6 months) and relatively late group (> 6 months) with the disease course of 6 months as the cut-off. Ultrasound parameters，such as rotator interval thickness index (RITI)

RI blood flow

coracohumeral ligament (CHL) thickness and coracohumeral ligament tortuosity，of the shoulders were analyzed and compared between groups. Meanwhile

the accuracy of the aforementioned indicators in diagnosing frozen shoulder was accessed. Result The average RITI and CHL thickness in frozen shoulder group were 10.10±1.73mm and 3.29±0.54mm

which were higher than those in control group

and the difference was statistically significant (P < 0.05). There were 12 cases of CHL tortuosity (12/35

34.3%) and 11 cases of positive RI blood flow (11/37

31.4%) in the frozen shoulder group

which were statistically significant different from the control group (P < 0.05). Values of AUC

sensitivity and specificity of RI

coracohumeral ligament thickness

RI blood flow and coracohumeral ligament tortuosity were correspondingly as follows:0.794

0.829 and 0.838 for RI respectively

0.868

0.800

0.811 for coracohumeral ligament thickness

0.630

0.314

0.946 for RI blood flow and 0.671

0.343

1.000 for coracohumeral ligament tortuosity. Compared with the relatively late frozen shoulder group

there were 10 patients (10/11

90.9%) with positive RI blood flow in the early group

which was significantly higher than the 1 patient (1/24

4.2%) with a course of >6M

and the difference was statistically significant (P < 0.05)

while RITI

coracohumeral ligament thickness and coracohumeral ligament tortuosity were not statistically significant (P > 0.05) between them. Conclusion Gray-scale ultrasound and Power Doppler evaluation of RI aid in the diagnosis of frozen shoulder

and positive RI blood flow is helpful for the judgment of the disease course

providing a basis for more accurate clinical treatment.