Macroscopic and histologic evaluation of a rat model of chronic rotator cuff tear

Background: The major cause of rotator cuff tears in humans is thought to be tendon degeneration. Although some studies have reported chronic rotator cuff tear models in animals, few studies of chronic rat models have demonstrated persistent defects for a relatively long time. The purpose of this study was to establish a chronic rotator cuff tear model in the rat and to evaluate the model macroscopically and histologically. Methods: Sixty Sprague Dawley rats were divided into 2 groups: tendon detachment only (tear group) and tendon detachment plus figure resin (chronic group). The contralateral shoulder served as a shamoperated control (sham group). In the tear group, the supraspinatus and infraspinatus tendons were completely detached. In addition to cuff detachment, figure resin was placed on the greater tuberosity to prevent cuff reattachment and scar formation in the chronic group. Macroscopic and histologic changes were assessed at 4 and 12 weeks after surgery. Results: A full-thickness cuff defect was observed in all chronic-group rats at both 4 and 12 weeks after surgery, and it could be repaired secondarily by traction in lower tension. However, no cuff defects were observed in the tear group because of obvious scar tissue formation. On histologic evaluation, progressive tendon degeneration, muscle atrophy, and fatty infiltration were observed in the chronic model at 12 weeks after surgery. Conclusion: We established a rat model of chronic rotator cuff tears using figure resin. This chronic rotator cuff tear model might be useful for further clinical investigations of rotator cuff repair. (C) 2016 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.