Biological and Biomechanical Evaluation of Autologous Tendon Combined with Ligament Advanced Reinforcement System Artificial Ligament in a Rabbit Model of Anterior Cruciate Ligament Reconstruction

Abstract

Objective: To compare the biomechanical and histological changes in a rabbit model after reconstructing the anterior cruciate ligament (ACL) with solely autologous tendon and with autologous tendon combined with the ligament advanced reinforcement system (LARS) artificial ligament.

Methods: Anterior cruciate ligament reconstruction was performed in 72 knees from 36 healthy New Zealand white rabbits (bodyweight, 2500-3000 g). The Achilles tendons were harvested bilaterally. The left ACL were reconstructed solely with autografts (autologous tendon group), while the right ACL were reconstructed with autografts combined with LARS ligaments (combined ligaments group). The gross observation, histological determination, and the tension failure loads in both groups were evaluated at 12 weeks (n = 18) and 24 weeks (n = 18) postoperatively.

Results: Gross examination of the knee joints showed that all combined ligaments were obviously covered by a connective tissue layer at 12 weeks, and were completely covered at 24 weeks. Fibrous tissue ingrowth was observed between fascicles and individual fibers in the bone-artificial ligament interface at both time points; this fibrovascular tissue layer localized at the bone-artificial ligament interface tended to be denser in specimens obtained at 24 weeks compared with those obtained at 12 weeks. The tension failure loads of the knees were similar in the autologous tendon group and the combined ligaments group at 12 weeks (144.15 ± 3.92 N vs. 140.88 ± 2.75 N; P > 0.05), and at 24 weeks (184.15 ± 1.96 N vs. 180.88 ± 3.21 N; P > 0.05).

Conclusion: Reconstructing the ACL in rabbits using autologous tendon combined with the LARS artificial ligament results in satisfactory biointegration, with no obvious immunological rejection between the autologous tendon and the artificial ligament, and is, therefore, a promising ACL reconstruction method.

Keywords: Anterior cruciate ligament; Autologous tendon; LARS artificial ligament; Reconstruction.

Figure 1

(A) The unfolded and clipped “LARS ligament” consisted of two parts, the intra‐articular portion was made of longitudinal and parallel fibers, the extra‐articular portion was made of transverse and crossing fibers. (B) The prepared “LARS ligament prosthesis” was composed of five cords of fiber, and the length was 80 mm and the diameter was 2 mm. LARS, ligament advanced reinforcement system.

Figure 2

The prepared “combined ligament prosthesis” was composed of an autologous tendon and the ligament advanced reinforcement system (LARS) ligament prosthesis; both ends were sutured by two No. 4‐0 Ethibond sutures.

Figure 3

(A) Anterior cruciate ligament reconstruction (ACLR) with an autologous tendon in the left knee; the graft materials were sutured to the surrounding tissue and fixed by steel wire. (B) ACLR with combined ligaments in the right knee; the graft materials were then sutured to the surrounding tissue and fixed by steel wire.

Figure 4

(A) The combined ligaments were obviously covered by a connective tissue layer at 12 weeks, and the connection between the bone and artificial ligaments interface had adequate tightness, but some parts were separated. (B) The combined ligaments were completely covered by collagen and synovial tissue at 24 weeks, autologous tendon fibers and ligament advanced reinforcement system (LARS) artificial ligament fibers were intertwined with each other, and there were more connective synovial fibers between the ligament and bone interface.

Figure 5

Histology of “combined ligaments” at 12 weeks (HE staining). (A) The bone‐artificial ligament interface was connected loosely. It is found that some parts are separated, and there was no obvious fiber connection between the bone–artificial ligament interface (HE × 100). (B) The ligament advanced reinforcement system (LARS) artificial ligament fiber bundle is clear and oriented; there are small amounts of synovial tissue among the fibers of the “LARS ligament prosthesis” at the bone‐artificial ligament interface (HE × 400); (C and D) In the intra‐articular parts, no collagen fibers ingrew into the ligament advanced reinforcement system (LARS) ligaments 12 weeks after implantation, and there were no infammatory cells between them (HE × 100 and HE × 400).

Figure 6

Histology of “combined ligaments” at 24 weeks. (A) There was no clear demarcation line between the bone and ligament, and the fibrous tissue was compact and closely connected with the ligament (HE × 100). (B) There was more synovial tissue among the fibers of “LARS ligament prosthesis,” and the collagen fibers were gradually filling LARS ligament fibers (HE × 400). (C and D) A small amount of collagen fibers ingrew into the intra‐articular parts of LARS ligaments 24 weeks after implantation, but there were still gaps between the collagen fibers and artificial materials (HE × 100 and HE × 400). (E and F) There were no obvious inflammatory cell infiltration between the autologous tendon and LARS ligaments in the intra‐articular parts of the joint (HE × 100 and HE × 400).

Figure 7

Histology of “autologous tendons” at 24 weeks (HE staining). (A) There was a small amount of new tissue in the tendon junction, the ligament‐bone interface was connected tightly. (B) It was closely connected with the surrounding tissue, and the connection between the ligament and bone interface was very compact, the collagen fiber was seen between the tendon graft and the bone tunnel (HE × 100 and HE × 400).