| Objective:1 Establish finite element model of proximal femur.2 With the help of three-dimentiona graphics software,femoral neck fracture models of three different Pauwels classification and four models of different internal fixation types were established,respectively,for the three cannulated compression screws in a triangle(a)and inverted triangle configuration(b),as well as four cannulated compression screws positioned in a rectangle(c)and diamond(d)configuration.3 To compare the stress distribution,displacement distribution of fracture site and interal fixator between these models with the help of Ansys,therefor,to make a deep comprehensive evaluation of biomechanical feature on each kinds of fixation and provide a theoretical basis and guidline for clinical applications.Methods:1 Construction of digital three-dimensional finite element model of femoral neck fracture: The including criteria is the hip without fracture,deformity,tumor,bone destruction confirmed by X-ray examination.The CT scan of proximal femur was taken under a 64-slice spinal CT(Siemens,Munich,Germany)to scan from upper of femoral head to inferior of lesser trochanter using a tube voltage of 120 k V,tube current of 200 m A,slice thickness of 1 mm,and interlayer spacing of 1 mm.The scanned data were exported in the DICOM format,and 250 DICOM images were obtained.Importing the images into the Mimics 14.0 software(Materialize Company,Leuven,Belgium).After determining threshold,three-dimensional reconstruction of a proximal femur was established,followed by exporting theSTL format data into Geomagic Studio 12.0 software(3D system Inc.,Rock Hill,SC,USA).The models were faired,cutted,migration,Boolean subtraction etc.Processing,to get more elaborated model files,save the results output in Iges format.The above fine models were then exported into Solid Works software to solid reconstruction,cut the fracture line into 30°,50°,70°.2 Construction of fixation models: three-dimensional models of the four types of internal fixation were established in Solid Works software were: a:three cannulated compression screws in a triangle configuration;b: three cannulated compression screws in an inverted triangle configuration,c: four cannulated compression screws positioned in a rectangle configuration and d:four cannulated compression screws positioned in a diamond configuration.The cannulated screw is 100 mm in length and 6.5 mm in diameter,threaded in the screw was ignored,which was established into three-dimentional models.The screws and the bone was positioned with each other,and after the screws were implanted,the skeleton of the screw region was removed by Boolean operation,and the nodes and elements were introduced into the finite element analysis software ANSYS,v12.1(ANSYS,Inc.,Canonsburg,PA,USA)for FEA.3 Material properties,boundary conditions and loading of finite element models: the above models were imported into the simulation software Ansys Workbench and then import into Mimics according to gray gives different material properties,import back into ANSYS to set boundary conditions,constraints and simulate femoral neck fracture conditions under stress.The material properties of the bones and internal fixation do not account for the friction between the joints and cartilage.This simplifies the processing with muscle and tendon.Thus,the fracture surface is completely broken and is in the contact state with a friction coefficient of 0.2.The DOF constrains the proximal femur shaft three-dimensional finite element model of the lower edge of all the nodes to 0 as the boundary conditions;i.e.,the distal end of each node on the X,Y,and Z axes has a displacement of 0.Using simplified models,the force on the femoral head from the pelvic acetabular fossa wasonly taken into consideration.We used only the greater trochanter near the abductor(gluteus medius muscle and piriformis)muscle force and vastus lateralis muscle force for finite element analysis,with 600 N of axial stress acting on the femoral head and the acetabular contact surface axially down;So as to simulate and calculate the force.4 Evaluation indexes: make a comprehensive analysis of the mechanical properties by the analysis of the three kinds of indicators of the four kinds of intemal fixation model(a~d):(1)The stress distribution and peak stress on internal fixation;(2)The displacement distribution of peak displacement on internal fixation and femoral head;(3)the stress distribution location and peak stress on fracture zone of the femoral head side.Results:Based on CT scan data of normal proximal femur using Mimics,Geomagic Studio,to establish a femoral neck fracture model,this method is feasible and effective modeling faster,and no harm to the human body.The three-dimensional finite element method is a theoretical biomechanical research methods,geometric model can simulate a variety of structures,given the biological material properties of the various organizations,can reflect the overall trend of the biomechanical properties,which can be used as a specimen experiment,is a good supplement method to biomechanics research.In this study,the use of a human femur CT data,with Mimics,Geomagic Studio,Solidworks,Anasys soft-ware,established the finite element model of normal human femoral neck fractures and has good geometric similarity.The model has a good physical similarity,more accurate and complete simulation of its mechanical characteristics of femoral neck fracture,conducive to their biomechanical analysis.Four screws in a diamond was the optimal screw configuration.For Pauwels I,the peak stresses on the screws and femoral head side for(a),(b),(c),and(d)were 46.382,32.159,43.985,and 24.342 MPa and 5.840,7.440,3.731,and 6.311 MPa,respectively;the displacement peaks were 0.610,0.608,0.598,and 0.595 mm,respectively.For Pauwels II,the peak stresses on thescrews and femoral head side for(a),(b),(c),and(d)were 46.763,39.979,49.619,and 25.692 MPa,and 4.971,7.332,3.161,and 5.734 MPa,respectively;the displacement peaks were 0.634,0.635,0.622,and 0.631 mm,respectively.For Pauwels III,the Peak stresses on the screws and femoral head side for(a),(b),(c),and(d)were 51.432,39.477,51.515,and 26.949 MPa,and 6.163,10.07,5.257,and 9.552 MPa,respectively;the displacement peaks were 0.662,0.654,0.644,and 0.644 mm,respectively.Conclusions:For the three Pauwels types,the displacement of four cannulated screws positioned in rectangle and diamond configuration is lesser than three cannulated screws in triangle or inverted triangle configuration,which can prevent femoral neck shortening and have much more bigger compression uppon fracture zone;The stress dispersion of a diamond posion is better than the other three type,so that the diamond position with four cannulated screws was the best screw configuration for femoral neck fracture fixation,which not only resulting in increased femoral neck fracture stability but reducing femoral neck shortening. 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