ABSTRACT
BACKGROUND: A high fracture of the mandibular condyle is often accompanied by cartilage damage. At the same time, the muscle attached to the condyle is avulsed and becomes a free bone mass. How to speed up the concurrent healing of cartilage during bone healing has always been a clinical difficulty and challenge. OBJECTIVE: To investigate the effect of parathyroid hormone on the healing of condylar cartilage in rabbits with high condylar fracture after free reduction. METHODS: An experimental model of free reduction and fixation of condylar fracture was established in 48 New Zealand big-eared rabbits, which were randomly divided into experimental group and control group (n=20 per group). The experimental group was injected with parathyroid hormone (20 μg/kg) subcutaneously every other day, and the control group was injected with 1 mL of normal saline. The animals were sacrificed at 1, 2, 3, and 4 weeks postoperatively. The mandible condyle was histologically observed. Immunohistochemistry staining and PCR were used to detect the expression of Sox9 and matrix metalloproteinase 13 in the condylar cartilage. The study protocol was approved by the Animal Experimental Ethics Committee of Guizhou Medical University (approval No. 1700456). RESULTS AND CONCLUSION: The results of safranine O-fast green staining and hematoxylin-eosin staining indicated that there were more chondrocytes and cartilage matrix deposition in the experimental group than the control group. In the immunohistochemistry, the average absorbance of Sox9 in the experimental group was significantly higher than that in the control group within 1-3 postoperative weeks (P < 0.05). The average absorbance of matrix metalloproteinase 13 in the experimental group was lower than that in the control group within 1-3 postoperative weeks (P < 0.05). The expression of Sox9 mRNA in the experimental group was significantly higher than that in the control group within 1-3 postoperative weeks, P < 0.05). The expression of matrix metalloproteinase 13 mRNA in the experimental group was significantly lower than that in the control group within 1-3 postoperative weeks (P < 0.05). These findings indicate that intermittent subcutaneous injection of parathyroid hormone can up-regulate the expression of Sox9, inhibit the expression of matrix metalloproteinase 13, promote the transformation of mesenchymal stem cells to cartilage, and accelerate the repair of cartilage damage.