Effect of scapular dyskinesis on supraspinatus repair healing in a rat model.

BACKGROUND: Rotator cuff tears are common conditions that often require surgical repair to improve function and to relieve pain. Unfortunately, repair failure remains a common problem after rotator cuff repair surgery. Several factors may contribute to repair failure, including age, tear size, and time from injury. However, the mechanical mechanisms resulting in repair failure are not well understood, making clinical management difficult. Specifically, altered scapular motion (termed scapular dyskinesis) may be one important and modifiable factor contributing to the risk of repair failure. Therefore, the objective of this study was to determine the effect of scapular dyskinesis on supraspinatus tendon healing after repair.

METHODS: A rat model of scapular dyskinesis was used. Seventy adult male Sprague-Dawley rats (400-450 g) were randomized into 2 groups: nerve transection of the accessory and long thoracic nerves (SD) or sham nerve transection (Sham control). After this procedure, all rats underwent unilateral detachment and repair of the supraspinatus tendon. All rats were sacrificed at 2, 4, and 8 weeks after surgery. Shoulder function, passive joint mechanics, and tendon properties (mechanical, histologic, organizational, and compositional) were evaluated.

RESULTS: Scapular dyskinesis alters joint function and may lead to compromised supraspinatus tendon properties. Specifically, diminished mechanical properties, altered histology, and decreased tendon organization were observed for some parameters.

CONCLUSION: This study identifies scapular dyskinesis as one underlying mechanism leading to compromise of supraspinatus healing after repair. Identifying modifiable factors that lead to compromised tendon healing will help improve clinical outcomes after repair.