Effect of extension on stiffness of the teres minor muscle following extracorporeal shock wave therapy for frozen shoulder: a double-blind, randomized, controlled trial.

[Purpose] The mechanism of action and the position and site of Radial pressure wave therapy are unclear. This study aimed to evaluate the effect of shoulder position on muscle stiffness after radial pressure wave therapy. [Participants and Methods] This randomized, double-blind, parallel-group controlled trial included 32 orthopedic clinic participants. Using the block replacement method, patients were randomly assigned to a stretching group (IR group) or a shortening group (0 group) in a 1:1 ratio. Muscle stiffness was measured using ultrasonography (GE LOGIQ S8) with a 9 MHz linear transducer in B mode. Measurements were performed along the long axes of the teres minor, infraspinatus, and deltoid muscles. Radial pressure wave therapy were applied only to the teres minor (3.0 bar, 12 Hz, 2,000 shots). Muscle stiffness testers were blinded to the upper limb position during Radial pressure wave therapy. [Results] Teres minor muscle stiffness was significantly decreased within and between groups, and the deltoid muscle stiffness was significantly decreased within groups in the IR group. [Conclusion] Radial pressure wave therapy applied with the muscle extended reduced muscle stiffness more than Radial pressure wave therapy applied in the shortening position.