Inhibitory Effect of Synovial Fluid on Tendon-to-Bone Healing: An Experimental Study in Rabbits

PurposeThe purpose of this study was to explore the effects of joint synovial fluid on tendon-to-bone healing in intra-articular ligament reconstruction of the knee.MethodsWe divided 40 female New Zealand white rabbits into 4 groups randomly, with 10 animals in each group. Transfer of the semitendinosus tendon to the tibial bone tunnel was performed to create tendon-to-bone healing models. An intra-articular bone tunnel (IBT) was used on the left side and an extra-articular bone tunnel (EBT) on the right. Histologic evaluation was performed at 2, 4, and 8 weeks after the operation and biomechanical testing at 8 weeks.ResultsOn the basis of fibroblast proliferation, collagen fiber density, collagen fiber orientation, and tendon-to-bone connection, histologic scores were significantly lower in the IBT group than in the EBT group at 2, 4, and 8 weeks. Cell counts per high-power field at the tendon-bone interface were significantly lower in the IBT group than in the EBT group at 2 and 4 weeks. In addition, biomechanical testing showed that the IBT group was significantly inferior to the EBT group in terms of ultimate failure load, yield load, and stiffness. There was also a significant difference between the 2 groups in failure mode.ConclusionsJoint synovial fluid appeared to have an inhibitory effect on tendon-to-bone healing in rabbits at an early stage.Clinical RelevanceOur findings imply that prevention of infiltration of joint synovial fluid into the bone tunnel might be beneficial in improving the clinical outcome of cruciate ligament reconstruction of the knee.