A comparative study of collagen morphology and joint strength in anterior cruciate ligament repair and reconstruction models in rabbits

Background and Aim: Anterior cruciate ligament (ACL) repair offers several theoretical advantages over reconstruction, including preservation of native proprioception and reduced donor-site morbidity. However, the current experimental models are predominantly limited to ACL reconstruction, leaving a critical gap in ACL repair research. This study introduces a novel rabbit model to evaluate osteointegration and mechanical strength at the tendon/ligament-bone interface following ACL repair and reconstruction. Materials and Methods: Six male New Zealand White rabbits (Oryctolagus cuniculus), aged 90 ± 0 days and weighing 2.50 ± 0.20 kg, were randomly assigned to two groups: ACL reconstruction (n = 3) using the extensor digitorum longus tendon graft and ACL repair (n = 3) using the Krackow suture technique at the femoral attachment. Specimens were collected 6 weeks postoperatively for histological evaluation of Sharpey’s-like fibers, immunohistochemical analysis of types I and III collagen, and biomechanical tensile testing. Results: All surgical procedures were completed without complications. Histological analysis showed greater numbers of Sharpey’s-like fibers in the reconstruction group (6.33 ± 0.58%) compared to the repair group (5.67 ± 1.6%), though not statistically significant (p > 0.05). Type I collagen fibers were significantly longer in the reconstruction group in both longitudinal (3.10 ± 0.05 μm vs. 2.97 ± 0.04 μm) and transverse (1.94 ± 0.09 μm vs. 1.81 ± 0.05 μm) dimensions (p < 0.05). Type III collagen dimensions did not differ significantly. The mean tensile failure load was higher in the reconstruction group (105.96 ± 63.37 N) than in the repair group (62.56 ± 20.11 N), though this difference was not statistically significant (p > 0.05). Conclusion: This study establishes a reproducible and cost-effective ACL repair model in rabbits and confirms that tendon-bone osteointegration occurs in both ACL repair and reconstruction. Superior biomechanical strength and enhanced type I collagen integration in the reconstruction group underscore current clinical outcomes favoring reconstruction. This model offers a valuable platform for exploring biological augmentation strategies to enhance ACL repair efficacy. Keywords: anterior cruciate ligament repair, biomechanics, osteointegration, rabbit model, type I collagen.