Background: Corticosteroid injection is a common treatment for frozen shoulder, but controversy still exists regarding the injection site with the best outcome.
Hypothesis: To treat the frozen shoulder in the freezing stage with corticosteroid injection, a single injection into the rotator interval (RI) could yield better effects in terms of improvement in pain, passive range of motion (ROM), and function than would an injection into the intra-articular (IA) or subacromial (SA) space.
Study design: Randomized controlled trial; Level of evidence, 1.
Methods: Patients with primary frozen shoulder in the freezing stage were randomized into 3 groups: RI injection, IA injection, or SA injection with corticosteroid. Clinical outcomes were documented at baseline and at 4, 8, and 12 weeks after intervention, including visual analog scale (VAS) for pain; passive ROM measurements, including external rotation, internal rotation, forward flexion, and abduction; and evaluation with the Disability of Arm, Hand, and Shoulder (DASH) score and Constant score.
Results: There were no significant differences in the basic properties of the 3 groups (27 in RI group, 24 in IA group, and 26 in SA group) before injection. Improvements in pain VAS, passive ROM, Constant score, and DASH score were faster and significant in the RI group from 4 weeks after injection, followed by those in the IA group. Passive ROM decreased and DASH score did not change significantly in the SA group, although pain VAS and Constant score improved significantly.
Conclusion: To treat frozen shoulder in the freezing stage with corticosteroid injection, a single injection into the RI yielded better effects in terms of improvement in pain, passive ROM, and function than did injections into the IA or SA space.
Keywords: adhesive capsulitis; corticosteroid injection; frozen shoulder; randomized controlled trial; rotator interval.