External axial stress in induction of rabbit tibia fracture healing

Abstract

Objective The objective of this study was to investigate whether postoperative rapping by external axial stress stimulator can accelerate rabbit tibial fracture union by analyzing the expression of vascular endothelial growth factors (VEGF), CD34, bone morphogenetic protein-2 (BMP-2) and transforming growth factor-β1 (TGF-β1) in different periods osteotylus. Methods New Zealand rabbit tibial fracture models were randomly divided into two groups. Experimental group received stress stimulation for 30 minutes every two days began at postoperative 8 days. Lane-Sandhu X-ray evaluation system was used to evaluate the bone healing process at 2, 4, 6 and 8 weeks. Specimens (n=6) were obtained for immunohistochemical test and semi quantitative analysis to compare the expression of VEGF, CD34, BMP-2 and TGF-β1 at postoperative 2, 4, 6 and 8 weeks. Results (1) The mean Lane-Sandhu X-ray score in experimental group was significantly higher than controlled group with more osteotylus quantity at 4, 6 and 8 weeks. At 4, 6, 8 weeks postoperation, the score of experimental group (5.33±0.54, 7.00±0.82, 9.67±0.47) was significantly higher than the control group (3.67±0.15, 5.67±0.44, 7.08±0.32, P<0.05). (2) The VEGF in the experimental group reached the peak at 4th week after operation, the density (mean) in the experimental group was (532.50±13.50) higher than that in the control group (319.18±12.09), P<0.05; BMP-2 peaked at the 6th week after operation and the density (mean) of the experimental group was reached. (571.79±7.97) was higher than that of the control group (296.10±12.99, P<0.01). CD34 peaked at the 4th week after operation, the density (mean) in the experimental group was (451.69±40.94) higher than that in the control group (252.65±14.49, P<0.01); TGF-β1 peaked at the 4th week too, the density (mean) in the experimental group was (433.78±3.41) higher than that in the control group (249.41±12.03, P<0.01). Conclusion Postoperative rapping by external axial stress stimulator can promote the expression of VEGF, CD34, BMP-2 and TGF-β1, stimulate vascularization and osteogenesis in the fracture site of rabbit tibia, therefore, accelerate the fracture union. Key words: Fracture union; Stress stimulation; Vascular endothelial growth factors; CD34; Bone morphogenetic protein-2; Transforming growth factor-β1