Optimizing tendon-to-bone healing: a comparative study of intratunnel and anatomical repairs in rotator cuff tears

Background: Rotator cuff tears are a leading cause of shoulder pain, with high rerupture rates despite advancements in surgical techniques. Tendon-to-bone healing failure is often attributed to insufficient fibrocartilage regeneration at the repair site. Intratunnel repair (TR) has been proposed as an alternative approach to enhance healing by increasing tendon-bone contact and exposure to marrow-derived stem cells. However, its effectiveness in chronic rotator cuff tears remains unclear. This study aims to compare the biomechanical and histological outcomes of TR and surface repair (SR) in a rabbit model. We hypothesized that TR might offer advantages in tendon-to-bone healing compared to SR, particularly through enhanced contact area and marrow exposure. Methods: A chronic rotator cuff tear model was created in 36 New Zealand White rabbits by tenotomizing the subscapularis tendon and preventing spontaneous healing for 8 weeks. The right shoulders underwent TR, while the left shoulders received SR. Biomechanical and histological evaluations were performed at 4, 8, and 12 weeks postrepair. Biomechanical testing assessed failure load, stiffness, and elongation. Histological assessments included collagen fiber organization, fibrocartilage formation, vascularity, and tendon maturation using Modified Watson tendon maturation scoring. Statistical analyses were conducted using nonparametric tests with a significance level of P < .05. Results: Biomechanical results showed no significant differences in failure load between TR and SR at any time point (P = .423, P = .423, P = .631). However, at 12 weeks, the stiffness of TR was significantly higher than SR (P = .005). Early histological findings showed similar tendon maturation, collagen alignment, and vascularity in both groups. By 12 weeks, the SR group exhibited significantly better collagen organization (P = .006), vascularity (P = .002), and Modified Watson tendon maturation score (P = .004) compared to TR. The tidemark line, a key indicator of fibrocartilage development, was observed in all SR samples at 12 weeks but was absent in most TR specimens. Discussion: Contrary to our hypothesis, TR did not demonstrate superior healing outcomes compared to SR. While TR provided similar biomechanical properties, its histological outcomes were inferior over time. We speculate that increased inflammatory response and tendon micromotion within the tunnel may have contributed to the inferior histological healing observed in the TR group. Conclusion: These findings suggest that TR does not offer significant advantages over SR in chronic rotator cuff tears. Further studies are needed to optimize healing strategies within the bone tunnel.