Comparative Efficacy of Rotator Interval Versus Posterior Capsule Approach Intraarticular Corticosteroid Injections for Primary Frozen Shoulder: A Single-blind, Randomized Trial

Background: Intraarticular (IA) corticosteroid injection is commonly performed in patients with primary frozen shoulder (PFS). However, the best administration site remains controversial. Objectives: To compare the efficacy of rotator interval (RI) vs posterior capsule (PC) approach for ultrasound-guided corticosteroid injections into the glenohumeral joint of patients with PFS. Study Design: A randomized, exploratory, prospective study. Setting: A single fellowship training institution in Daegu, Republic of Korea. Methods: This study was approved by the Institutional Review Board (2019-04-047-001). Ninety patients with PFS were randomly assigned to either RI approach (RI group, n = 43) or PC approach (PC group, n = 45) for ultrasound-guided IA corticosteroid injection. Fluoroscopic images to assess the accuracy of the injection were obtained immediately after injection by a shoulder specialist. Visual Analog Scale for pain, the American Shoulder and Elbow Surgeons score, the subjective shoulder value, and range of motion (ROM) were used to assess clinical outcomes for all patients at the time of presentation, and at 3, 6, and 12 weeks after injection. Results: The accuracy of injection was 76.7% (33/43) and 93.3% (42/45) in the RI and PC groups, respectively; the between-group difference was statistically significant (P= .028). Significant improvements were observed in both groups in terms of all clinical scores and ROMs throughout follow-up until 12 weeks after the injection (all P< .001). At 12 weeks, better improvements in forward flexion and abduction (P = .049 and .044) were observed in the RI group than in the PC group. No adverse effect related to injection was observed in either group. Limitations: This study had no control group receiving placebo injections and limited follow-up time. Conclusions: Both groups showed significant pain reduction and functional improvement until 12 weeks after injection. Although no significant differences were observed in pain and functional scores between the 2 groups, the RI group showed better improvement of ROM than the PC group. These results indicate that the RI and anterior structures are a major site in the pathogenesis and treatment target of PFS.