ABSTRACT
BACKGROUND: No conclusion has yet been drawn on the effect of bone morphogenetic protein-2 (BMP-2)/collagen type I hydrogels on tendon-bone healing during the reconstruction of anterior cruciate ligament (ACL) is inconclusive. OBJECTIVE: To investigate the effect of BMP-2/collagen type I hydrogels to repair ACL injury. METHODS: ACL injury models were made in the right knees of 18 New Zealand rabbits. Model rabbits were randomized into three groups: blank control group with no intervention, control group with implantation of autologous semitendinosus tendon into the tibial and femoral tunnels, and experimental group with implantation of autologous semitendinosus tendon into the tibial and femoral tunnels combined with BMP-2/collagen type I hydrogel injection into the tibial tunnel. The Micro-CT, hematoxylin-eosin staining and Masson staining of the tendon-bone interface were conducted at 3 months after implantation. RESULTS AND CONCLUSION: (1) Micro-CT imaging examination: No obvious bone tissue regeneration around the tibial tunnel (at the opening site, 1 cm distant to the opening site, and at the widest site of the tunnel) was observed in the blank control group. Discontinuous bone regeneration in the tibial tunnel was found in the control group. In the experimental group, there was obvious tendon-bone regeneration and continuous bone connections in part of the tibial tunnel. (2) Hematoxylin-eosin staining: In the blank control group, sparse fibrous tissue and regenerated bone tissue were observed in the bone tunnel. In the control group, new bone tissues grew into the tendon, but the tendon and the surrounding tissue were loose, with a large amount of fibrocytes and the small new bone area. In the experimental group, a large number of new bone tissues were regenerated in the tendon, the tendon was intertwined with the surrounding bone tissues, and the area of new bone was increased. (3) Masson staining: In the blank control group the tunnel was partially filled with fat or fibrous tissues, and no tendon-bone interface appeared. In the control group, cartilage and fibrous tissues were visible on the tendon-bone interface, but the fibrous tissues were loosely arranged and had no close connection with the cartilage tissues. In the experimental group, fibrous-chondral-bone tissues were found on the tendon-bone interface, with fibrous tissues being tightly bound to the cartilage tissues, and mature bone tissues were visible below the cartilage tissue. These results indicate that BMP-2/collagen type I hydrogel is beneficial to ACL repair by strengthening the bone regeneration in the bone tunnel and the healing of tendon-bone junction.