Expression Of RANKL/OPG In The Process Of Bone Healing After Free Reduction Of Mandibular Condylar Fracture Induced By Parathyroid Hormone

Objective:To explore the effects and mechanisms of intermittent subcutaneous injection of Parathyroid hormone(PTH)on bone healing after free reduction of rabbit condylar fracture.Methods:A total of 48 New Zealand rabbits aged 5-6 months were randomly divided into experimental group and control group,with 24 rabbits in each group.The experimental models of free reduction and internal fixation of mandibular condylar fracture were established in the experimental group and control group,and subcutaneously injected PTH 20μg/kg and 1 m L of normal saline on the next day after surgery,respectively.At 1,2,3 and 4 weeks after surgery,the bone specimens were collected to observe the healing situation.The expressions of osteoprotegerin(OPG),receptor activator of NF-κB ligand(RANKL)and runt-related transcription factor 2Runx2 in the fracture area were detected by immunohistochemical staining and PCR.Results:In the same period of time,osteoblasts in the fracture area of the experimental group were more,new callus was faster and the density was higher.The number of osteoclasts in experimental group was less than that in control group 4 weeks after operation(P< 0.05).The immunohistochemical IOD value and m RNA relative expression level of OPG showed that the expression level of the experimental group was higher than that of the control group in 4 weeks after operation.The immunohistochemical IOD value and m RNA relative expression level of RANKL showed that the expression level of the experimental group was lower than that of the control group in 4 weeks after surgery(P < 0.05).The immunohistochemical IOD value and m RNA relative expression level of Runx2 showed that the experimental group was higher than the control group during 2-4 weeks after surgery(P < 0.05).Conclusions:The application of PTH on the next day after free reduction of mandibular condylar fracture can accelerate the formation of new bone and inhibit the activation of osteoclasts in the fracture region by up-regulating the expressions of OPG and Runx2 and inhibiting the expression of RANKL in the early postoperative stage,thus promoting fracture healing after free reduction of mandibular condylar fracture.