Biomechanical and histological evaluation of aspirin in rotator cuff tear rat model

Background: Aspirin is a representative non-steroidal anti-inflammatory drug (NSAIDs) and has been commonly used for the treatment of tendinopathy in clinical practice. In this study, we aimed to evaluate the biomechanical and histological healing effects of aspirin on the healing of the tendon-to-bone interface after rotator cuff tear repair. Methods: A total of 20 male Sprague-Dawley rats were randomly divided into two groups of 10 rats each. Group-C performed repaironly, and group-aspirin treated with aspirin after tendon repair. Group-aspirin rat were intraperitoneally injected with aspirin at 10 mg/kg every 24 h for 7 days. Eight weeks after surgery, the left shoulder of each rat was used for histological analysis and the right shoulder for biomechanical analysis. Results: In the biomechanical analysis, there was no significant difference in load-to-failure (group-C: 0.61 +/- 0.32 N, group-aspirin: 0.74 +/- 0.91 N; p = .697) and ultimate stress (group-C: 0.05 +/- 0.01 MPa, group-aspirin: 0.29 +/- 0.43 MPa; p = .095). For the elongation (group-C: 222.62 +/- 57.98%, group-aspirin: 194.75 +/- 75.16%; p = .028), group-aspirin confirmed a lower elongation level than group-C. In the histological evaluation, the Bonar score confirmed significant differences in collagen fiber density (group-C: 1.60 +/- 0.52, group-aspirin: 2.60 +/- 0.52, p = .001) and vascularity (group-C: 1.00 +/- 0.47, group-aspirin: 2.20 +/- 0.63, p = .001) between the groups. Conclusions: Aspirin injection after rotator cuff tear repair may enhance the healing effect during the early remodeling phase of tendon healing.