Exercise Initiation After Surgical Reconstruction for Rat Rotator Cuff Injury Affects Tendon Healing and Muscle Preservation

Rotator cuff tear is a common disease, and surgical repair is often conducted, but the re-tear rate after surgery is still high. Mechanical stress is the key factor that promotes tendon healing, but the optimal exercise protocol to induce rotator cuff healing is unknown. This study aimed to elucidate the effects of postoperative exercise initiation timing on tendon healing and muscle degeneration after rotator cuff tear and reconstruction by controlling the shoulder joint motion with immobilization and exercise intervention. A total of 110 Wistar rats were used in this study and the supraspinatus tendon tear and reconstruction were performed. Animals were divided into five groups: (1) Sham surgery (Sham), (2) Cage activity (CA), (3) Immobilization (IM), (4) Immobilization + Early exercise (IM + EE), (5) Immobilization + Delayed exercise (IM + DE). At postoperative 3 and 6 weeks, the specimens were harvested for histological analysis and biomechanical testing. At 3 weeks, histological analysis using the Movin score was significantly higher in the IM + EE group compared to the IM group. Also, fiber arrangement was significantly higher in the CA, IM + DE group compared to the IM group. At 6 weeks, IM + EE had higher vascularity than the IM group and decreased collagen stainability than the IM + DE group. The results of biomechanical testing showed no significant differences between Sham and IM + EE at 3 weeks and Sham and IM at 6 weeks. Our results suggested that intermittent exercise under immobilization, particularly intermediate-intensity exercise intervention such as treadmill exercise from the inflammatory phase, was shown to delay the tendon healing process.