Establishment of a novel rat extra-articular tendon-to-bone transplanting healing model

Abstract

Objective To establish a novel rat tendon-to-bone healing model with a free tendon graft implanted into an extra-articular bone tunnel and to evaluate the effectiveness of this model for early tendon-to-bone healing process by histologic, biomechanical and radiological analysis. Methods Museulus flexor digitorum superficialis harvested from the left hind legs of 28 male Wistar rats were prepared as free autografts. Each autograft was implanted into a bone tunnel of 1.2 mm diameter created at ipsilateral proximal tibia1 metaphysis. The healing process of the tendon-to-bone interface tissuewas analyzed at week 1, 2, 4and 6 （n=4） after the transplantation. Biomeehanical test including maximum anti-pullout strength and failure mode were evaluated at week 2 and 6 （n=6） after transplantation. Immediately after the biomeehanical test, the samples were also taken by the high-resolu- tion radiography to observe the bone remodeling around the tunnel. Results At week 1, the interface between tendon graft and bone was primarily composed of a layer of amorphous fibrous granulation tissue. The thickness of the interface tissue decreased with the passage of time. This thinning tissue was gradually replaced by the newly formed bone tissue around the tunnel. The inter-face tissue almost disappeared at week 6 with a bunch of anchor fibers connecting the tendon with bone. The failure load-to-tunnel length ratio was significantly higher at week 6 [（1.00±0.30） N/mm] than that at week 2 [（0.35±0.17） N/mm]. The specimens of the tendon-to-bone complex failed by pull-out of the tendon from the bone tunnel at week 2, which translated into a break of the tendon at week 6. High-resolution X-ray imaging shows a clear gap around the bone tunnel at week 2. At week 6, the interface gap became blurred and the bone density at the tunnel site was similar to the surrounding bone tissue. Conclusion The healing pro-cess of a free tendon grant in an extra-articular bone tunnel is similar to that of the intra-articular anterior cruciate ligament recon-struction model. With simple surgical procedure and minimal influence to the postoperative activity, this tendon-to-bone healing model is of particular significance for early studies of tendon-to-bone healing process. Key words: Anterior cruciate ligament reconstruction; Models, animal; Rats