Enhancement Of Tendon-to-bone Healing By The Use Of Osteoinductive Biomaterials

ObjectiveAnterior cruciate ligament(ACL) is an important structure for knee normal function. After it injured the knee will occur instability and follow by the knee degenerative. It lead to knee dysfunction and influence patients routine life. So it is important to reconstruct ACL and to recover stability of knee. The technique of reconstruction ACL with autologous hamstring became popular for its advantage: little lesion to donor site, non-interferce to knee stretch system and anatomy reconstruction ACL. But there are a few of defects in this procedure. The process of tendon to bone healing is longer so that it can't allow early rehabilition exercise. The healing strength of tendon to bone is uncertain so that it affect the results of ACL reconstruction. Therefore,at present it is an investigate focal thing to enhance tendon to bone healing . Osteoinductive biomaterials have proved to be very osteoinductive and used to repair bony defects and ununion, but there has little research about its effect to tendon to bone healing. In this experiment, we established ACL reconstruction animal model with autologous flexor digitorum longus tendon and put a kinds of osteoinductive biomaterial(Tricalcium phosphate TCP) into the interface of tendon to bone , explore the enhancement of tendon to bone by use of osteoinductive biomaterial, investigate the healing process of tendon in bone tunnel, and observe the stage of histology of tendon. What we did is to offer theory basis for clinical apply in ACL reconstruction.Material and MethodsACL reconstructions were performed on both knees of 48 beagle dogs with the tendon of flexor degitorum longus, with suspension fixation technique. The tendon graft filled only the tunnel part near the joint. On the experimental side, injectable tricalcium phosphate was used to fill the tunnel near both end of the tendon graft. On the control side, no such injection was performed. Eight dogs were sacrificed respectively 2, 4, 6, 8, 10, and 12 weeks after surgery, three for histological examination and five for mechanical examination each time.ResultsHistological examination showed that on the experimental side, most of the tendon-bone interspace was filled with TCP island and surrounding osteoblast at 2 weeks. At 4 weeks, bone island formed in the TCP material and iregular Sharpey fiber appered. At 6 weeks, newly formed bone and regular Sharpey fiber filled all the interspace. At 8 weeks, the Sharpey fiber appear in bundle shape. At 10 weeks, fibrocartilage was found. At 12 weeks, calcified cartilage appeared in the tendon-bone interspace and approximately normal ACL insertion was shown. Contrast to the experimental side, on the control side, bone formation was apparent and spare Sharpey fibers were founded in the tendon-bone interspace 8 weeks after surgery. At 12 weeks, Sharpey fibers formed like those on the experimental side at 6 weeks. Mechanical examination showed that within 6 weeks, the pull-out strength was higher on the experimental side than on the control side, and there was statistical significant difference between the results.Conclusion1. Injectable TCP filling in the tunnel can enhance tendon-bone healing which was directly linked , and tendon-bone conjunction is similar to normal ACL insertion.2. Osteoinductive biomaterials can advance the process of tendon-bone healing by inducing new bone formation between interface of tendon to bone, so it can reinforce the tendon-bone healing strength.