Abstract: Abstract: Objective To investigate the therapeutic effects of combined variable stress plate fixation on experimental sheep femoral fracture healing. Methods Thirty healthy adult goats were successfully constructed with the model of right lower limb femur fracture, and model animals were equally divided into the experimental group (given the combined variable stress plate fixation) and the control group (given the common straight steel plate fixation). The goats were sacrificed at 4weeks, 8 weeks and 12 weeks after operation, and the broken end tissues of femur were taken for observation in imaging and histopathologic changes. The changes of thickness of cortical bone and diameter of medullary cavity were measured in two groups. The stress shielding effect of the plate was evaluated. The changes of bone trabecular density in callus offracture end were measured to evaluate fracture healing in two groups. The number of osteoclasts was used to evaluate bone callus remodeling in the process of fracture healing in the two groups. Results There were no significant differences inthe thickness of cortical bone and diameter of medullary cavity at 4 weeks between two groups. There were no significant differences in the thickness of cortical bone and diameter of medullary cavity between 4, 8 and 12 weeks in the experimental group. The diameter of bone medullary cavity was significantly higher in the control group than that of the experimental group at 8 and 12 weeks after treatment. The bone cortical thickness was significantly lower in the control group than that of the experimental group, which indicated that there was stress shielding effect in the control group, and there was no obvious stress shielding effect in the experimental group resulted in the loss of bone thickness. The bone trabecular density in callus of fracture was significantly higher in the experimental group than that in the control group at 4 and 8 weeks after treatment,suggesting that the rapidly bone formation in experimental group. The osteoclasts surrounding bone trabecular were significantly more at 8 weeks in the experimental group than those in the control group, but osteoclasts were significantly lower in the experimental group than those in the control group at 12 weeks, suggesting that the callus remodeling appeared earlier in the experimental group, and bone callus remodeling was basically over at 12 weeks in the experimental group.Conclusion Combined variable stress plate fixation can promote callus formation, accelerate callus reconstruction and promote fracture healing.

Key words: femoral fractures, fracture healing, fracture fixation, internal goats, combined variable stress plate