| Summary: | Background: Adhesive capsulitis (AC) is characterized by pain and limited range of motion, caused by stiffness of the joint capsule and coracohumeral ligament. On the other hand, there have been few reports on muscle stiffness in AC. The purpose of this study was to assess muscle stiffness in patients of AC with a portable and noninvasive device, Myoton PRO. We hypothesized that muscle stiffness around shoulder joint increases in AC. Methods: At first, we surveyed correlation between Myoton PRO and shear wave elastography with phantoms. Second, reproducibility and repeatability of healthy volunteers with Myoton PRO were evaluated. Finally, muscle stiffness was measured in 40 patients who were diagnosed with AC. Muscle stiffness was quantitatively measured with Myoton PRO. We compared the stiffness of the anterior deltoid (AD), pectoralis major, and latissimus dorsi (LD) in AC patients on both the affected and nonaffected sides. Results: Correlation coefficient in shear wave elastography and Myoton PRO was 0.99(P = .001). Reliability of intraoperator and interoperator with Myoton PRO was 0.9 or higher. Muscle stiffness values (N/m) of the AD, pectoralis major, and LD were 355 ± 61, 252 ± 54, 207 ± 51 in the affected sides and 328 ± 50, 252 ± 41, 186 ± 37 in the nonaffected sides, and the differences were significant in the AD and LD (P = .005, P = .002, respectively). Conclusions: We used Myoton PRO to evaluate muscle stiffness in AC. The AD and LD muscles of AC patients were significantly stiffer on the affected side compared to the nonaffected side.
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