Abstract: Objective To explore the mechanism of extracorporeal shock wave therapy (ESWT) to improve the distraction osteogenesis of rat femur by activating Wnt5a/Ca2+ signal. 
 Methods Sixty 8-week-old Sprague Dawley male rats were divided into a control group, a femoral traction model group, and an ESWT group (n=20). Rat gait parameters were measured using the CatWalk XT system, and the morphology of rat femur was analyzed through Micro-CT scanning. The histopathological grading was performed using the Mankin scoring standard, and the percentage of Wnt5a positive cells in each region of the subchondral bone was analyzed. Real-time polymerase chain reaction (RT-PCR) was used to analyze type Ⅰ collagen and osteopontin mRNA expression in rat femur. Immunohistochemical staining was used to analyze the expression of bone morphogenetic protein 2 (BMP2), vascular endothelial growth factor (VEGF), and proliferating cell nuclear antigen (PCNA). Western blot was used to analyze Wnt5a/Ca2+ signaling pathway protein expression. 
 Results The swing speed, maximum contact area, single standing posture, duty cycle and stent swing time of rats in the model group were lower than those in the control group, while the swing speed, maximum contact area, single standing posture, duty cycle and stent swing time of rats in the ESWT group were higher than those in the model group (P＜0.05). The trabecular volume fraction, trabecular thickness and bone mineral density of rats were lower in the model group than in the control group, but higher in the ESWT group than in the model group (P＜0.05). The Mankin score of the femoral joint in the model group was higher than that in the control group, while the number of Wnt5a positive cells in the model group was lower than that in the control group; The Mankin score of the femoral joint in the ESWT group was lower than that in the model group, while the number of Wnt5a positive cells in the ESWT group was higher than that in the model group (P＜0.05). Compared with the control group, osteocyte lacunae could be seen in the superficial area of subchondral bone plate in the model group, and the degree of injury on the femoral joint surface in the ESWT group was significantly reduced (P＜0.05). The Wnt5a marker of ESWT-induced model rats increased significantly (P＜0.05). The expression of type Ⅰ collagen and osteopontin mRNA was lower in the model group than in the control group, but higher in the ESWT group than in the model group (P＜0.05). Compared with the control group, the positive cells of BMP2, VEGF and PCNA staining in the model group decreased, while the positive cells of BMP2, VEGF and PCNA staining in the ESWT group increased, as compared with the model group (P＜0.05). The expression of CaMKⅡ, PLC and Wnt5a protein and the expression of PKC protein in the model group were higher than those in the control group, while the expression of CaMKⅡ, PLC and Wnt5a protein and the expression of PKC protein in the ESWT group were lower than those in the model group (P＜0.05). 
 Conclusion ESWT can promote the formation of angiogenesis, cell proliferation and the expression of osteoblast growth factors by activating the Wnt5a/Ca2+ signaling pathway, improve the bone mechanical performance and accelerate bone mineralization. 

Key words: Femur, Osteogenesis, Distraction, Extracorporeal shock wave therapy