BACKGROUND:Intramedullary nail has achieved a good clinical result in the treatment of femoral shaft fractures,but some patients still have aseptic nonunion due to mechanical instability.The femur is the longest and largest bone in the human body,but there are few studies on whether the fracture of the femur has different biomechanical results in different areas and the influence of different inserting methods on the stability of fracture fragments in different areas. OBJECTIVE:To analyze the biomechanical characteristics of anterograde and retrograde intramedullary nails in the treatment of different areas of femoral shaft fractures,and to evaluate the best way of insertion to reduce the incidence of nonunion. METHODS:CT data of a healthy volunteer were selected to import into the software of Mimics 19.0 and Geomagic studio 2017 to extract and optimize the three-dimensional model of the right femur.The anterograde and retrograde intramedullary nail models were built with Solidworks 2017 software and assembled with femoral shaft fracture models at different fracture areas according to standard surgical techniques.The models were imported into Abaqus 2017 software in STEP format to set material attribute parameters,boundary conditions,load and submit calculation,and the results were viewed in the visualization module.Among them,the antegrade and retrograde intramedullary nails of the upper femoral shaft fracture were A1 and A2 models,B1 and B2 models in the middle segment,and C1 and C2 models in the lower segment. RESULTS AND CONCLUSION:(1)In models A1,B1 and C2,the overall stress distribution of the femur was more uniform,and the placement,the displacement and angle of the fracture site,and inversion angle of the proximal femoral bone fragment were smaller.(2)For the upper and middle femoral shaft fractures,the anterograde intramedullary nail has a better biomechanical effect.For lower femoral shaft fractures,a retrograde intramedullary nail is preferable.

OBJECTIVE： To investigate the effects and its mechanism of calcium phosphate bone cement （CPC） loading total flavonoids of Davallia mariesii on osteogenic differentiation of induced membrane in rats. METHODS： Drug-loading CPC and drug-loading polymethyl methacrylate （PMMA） cement were prepared with the contents of Qianggu capsules （total flavonoids of D. mariesii as active ingredient） using CPC and PMMA cement as carrier. Totally 64 male SD rats were randomly divided into drug-loading CPC group， drug-loading PMMA cement group， no-drug CPC group， no-drug PMMA cement group， with 16 rats in each group. The femur of rats was separated and osteotomized to prepare bone defect model， and then the corresponding bone cement was implanted. Four weeks after modeling， the induced membranes of rats were cut and protected. Bone cement was taken out and autogenous cancellous bone was implanted. At the 4th week after modeling， X-ray photographs were taken on the hind limb bones of rats. At the 4th week after modeling and 6th week after bone grafting， induced membranes and new bone were taken from the bone defect area of rats respectively. HE staining was used to observe the morphology of induced membrane， and the width of bone rabecular and the number of osteoblasts of new bone tissue were measured. Immunohistochemistry was used to detect the protein expression of BMP-2 and VEGF in induced membrane. Western blotting assay was used to detect the protein expression of Smad1， Smad4 and Smad7 in new bone. RESULTS： Compared with other 3 groups， the degradation of bone cement in drug-loading CPC group was more obvious in the bone defect areas， which showed that the formation of induced membrane was observed and the bone defect areas were smaller； capillary endothelial cells were abundant and orderly arranged in the induced membranes， and the width of bone trabeculae and the number of osteoblasts in the new bone tissue increased significantly （P＜0.05）； the protein expression of BMP-2 and VEGF in the induced membrane， the protein expression of Smad1， Smad4 and Smad7 in new bone were increased significantly （P＜0.05）. CONCLUSIONS： CPC loading total flavonoids of D. mariesii promotes the formation of induced membrane osteoblast in bone defect model rats， which may be associated with regulating osteoblast differentiation by activating BMP-2/Smad pathway； at the same time， it can promote bone healing by promoting the differentiation of vascular endothelial cells， accelerating the formation of capillary network and increasing the expression of vascular endothelial cells.