Effect of extracorporeal shock-wave on tendon-bone healing after reconstruction of anterior cruciate ligament: A histological study in rabbits

Objective To observe the effect of extracorporeal shock wave（ESW） on tendon-bone healing after reconstruction of anterior cruciate ligament（ACL）. Methods Eighteen healthy F/M New Zealand white rabbits at the age of 2-3 months were randomly divided into ESW treatment group and control group. An animal model of ACL reconstruction was established using digital long extensor tendon. Rabbits in ESW group were treated with ESW 24 hours after ACL reconstruction while those in control group were not treated with ESW. Samples were collected when the animals were killed 2, 4 and 8 weeks after operation and stained with hematoxylin and eosin（HE） to observe changes in tendon-bone healing tissue. Intravascular ink injection was used to observe neovascularization in tendon-bone healing tissue. Results Active proliferation of fibroblasts and chondroblasts was observed on the tendon-bone interface and the number of collagen fibers was significantly increased and regularly arranged in ESW treatment group 4 weeks after operation. The healing tissue on bone-tendon interface was linked with dense connective tissue with a large number of collagen fibers which were regularly and longitudinally arranged. Collagen fibers, fibrocartilage and bone tissues with a direct ligamentous insertion-like structure could be found on tendon-bone interface in some transition zones 8 weeks after operation. The tissue on tendon-bone interface was healed quicker in ESW treatment group than in control group. The number of neo-vessels on tendon-bone interface was significantly greater in ESW treatment group than in control group 4 and 8 weeks after operation（P＜0.05）. Conclusion ESW can induce generation of neo-vessels, improve blood supply and promote tissue healing on the tendon-bone interface.