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

Abstract

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.

Figure 1

(a) The extensor digitorum longi tendon was identified after arthrotomy. (b)Tendon autograph preparation; suturing of the proximal edge of the tendon graft using the Krackow technique. (c) The tendon graft is 2 cm in length.

Figure 2

(a) Transection of anterior cruciate ligament attachment in medial site of the lateral femoral condyle. (b) Suture of the ligament edge using the Krackow technique. (c) The suture was passed through the femoral tunnels with the help of needle 23 and knots were made until the size of the knot exceeded the diameter of the bone tunnel.

Figure 3

(a) Tunnel preparation; 1.8 mm Kirschner wire was drilled at the anatomical insertions of the anterior cruciate ligament in the tibia and in (b) femur. (c) The tendon graft was passed through the tunnels with the help of needle 23. (d) It started from the tibial tunnel, (e) then continued through the femoral tunnel so that part of the tendon graft enters the tunnel. (f) The tendon graft ends under tension with their sutures, knots were made up to 6 times in the tibial and femoral side until the size of the knot exceeds the diameter of the bone tunnel and resembles an endobutton implant.

Figure 4

(a) Patients who underwent anterior cruciate ligament (ACL) reconstruction. Sharpey’s-like fibers are visible in more numbers than in image B (b), which is the group that underwent ACL repair.

Figure 5

(a–d) Longitudinal and transverse fiber lengths of types I and III collagen in the reconstruction and repair groups.

Figure 6

(a) The group that underwent anterior cruciate ligament (ACL) reconstruction and has a longer transverse length of type I collagen fibers than (b), which underwent ACL repair. (c) The group that underwent ACL reconstruction and has a longer transverse length of type III collagen fibers than (d) that underwent ACL repair. Bars, 20 μm.

Figure 7

The femur-ligament-tibia complex was fixed in a custom iron device and clamped to an Instron machine for biomechanical testing. (b) The arrow indicates the site of ligament rupture after the tensile test. The location of the ligament rupture is the attachment of the anterior cruciate ligament to the femur bone, which is the bone-ligament interface. This is the location where the ligament tissue and bone meet. (c) The average failure load in the repair group was lower than that in the reconstruction group at 6 weeks postoperatively; however, the difference was not statistically significant. (d) The ligament elongation before failure (Δ L at failure load) between two groups also not statistically different.