Relationships between posterior shoulder muscle stiffness and rotation in patients with stiff shoulder

OBJECTIVE: The aim of this study was to investigate differences in muscle stiffness between subjects with stiff shoulders and controls, and to determine the correlation between posterior shoulder muscle stiffness and range of motion of rotation. DESIGN: Prospective, cross-sectional study. SUBJECTS: Twenty subjects with stiff shoulder and 20 healthy subjects. METHODS: Range of motion of rotation, and stiffness in 4 muscles (posterior deltoid, infraspinatus, teres minor and teres major), were measured in affected shoulders and control shoulders using a goniometer and a Myotonometer, respectively. RESULTS: Patients with stiff shoulder had greater muscle stiffness than controls. Except for the teres major, significant correlations were found between internal rotation and stiffness of 3 muscles (r = 0.57-0.72). Among these 3 muscles, posterior deltoid muscle stiffness accounted for 51% of the variance in shoulder internal rotation beyond stiffness from the infraspinatus and teres minor muscles. CONCLUSION: These findings support that muscle stiffness is related to shoulder range of motion. It is important to consider the posterior deltoid, infraspinatus, and teres minor muscles in the rehabilitation of patients with restricted internal rotation of the shoulder.