Development of a Shoulder Contracture Model in Rats

Hypothesis The capsular tissue is responsible for the pathogenesis of the shoulder contracture. Materials and methods The glenohumeral joint of Sprague-Dawley rats was immobilized using internal fixation (immobilized group). The control group underwent a sham operation (sham group). To assess the range of motion, the glenohumeral joint angle was measured repeatedly under same torque in 6 conditions: after removal from the trunk, after removal of the outer muscles other than rotator cuff after removal of the rotator cuff muscles, and after 3 types of partial capsulotomy. The abduction angle and total rotation angles were measured. The length of the synovial intima was measured with hematoxylin-eosin–stained specimens. Immunohistochemical study for type III collagen was also performed. Results No significant differences were found in the range of motion until all the muscles were removed. The abduction angle increased significantly after serial capsulotomy in the immobilized group. Even after the capsulotomy, however, this angle remained significantly less than that in the sham group. There was a similar trend for the total rotation angle. There was morphological change in the synovium of the immobilized group; the significant decrease of synovial length and strong staining of type III collagen. Discussion Our results show that capsule might play important role for contracture formation. Decrease of the synovial length might reflect synovial adhesion. Strong expression in Type III collagen might be related to joint stiffness. Conclusion A contracture model was successfully established. Changes in the capsule and synovium might play an important role in occurrence of contracture.