| Objective: To research the biomechanical characteristics of Pauwels? femoral neck fracture using medial support plate combined with cannulated compression screws though the three-dimensional finite element technique,which provided a theoretical basis for clinical treatment of Pauwels? femoral neck fractures.Method: 1.Building a femur geometric model:A 44-year-old healthy male volunteer was recruited without femoral fracture,deformity and tumor that causing destroy of bone structure by inquiring the medical history and X-ray examination.Using a GE 64-row spiral CT scanner,a layer thickness of 0.625 mm CT scan of the femur was performed,and the CT image was stored as a DICOM format file into the medical three-dimensional reconstruction software Mimics 19.0.The three-dimensional model of the femur was extracted with profile line,thresholding,CT Bone Segmentation,and Calculating Masks in Mimics,then exported as a STL format file.The director parallel to the axel of femoral neck was simulated in the simulate action of Reslice Project,then the femur model and director were imposed in Geomagic Studio2012 with a STL format file for smoothing,meshing and fitting surface processing and also incorporated into the Solidworks 2018 software.2.Building the Pauwels? femoral neck fracture models:The proximal femoral bone model was incorporated into Solidworks2018 software,the femoral neck was segmented with 50°,60°,70° to the horizontal plane in the frontal plane,to develop three solid models.3.Building the internal fixation model:Cannulated screws and the inner steel plate which 3-hole 1/3 reconstruction tubular steel plate were fabricated using Solidworks software according to the clinical data.Assembly of the instruction: The cannulated compression screws was assembled into each fracture model in an inverted triangle parallel to the central axis of the thigh neck by virtual nail guide,and remove interference,then the fracture internal fixation model of group A(cannulated compression screws)was obtained.Based on the above the traditional cannulated screw models(group A),the medial support plate and matching screw was placed on the inner side of the femoral neck in SolidWorks softwarel,subsequently the internal fixation model of group B(medial support plate combined with three cannulated compression screws)was obtained.4.Meshing and Conditional assumptions and material parameter settings:the models were incorporated into Hypermesh14.0 software for meshing,and then the meshing models were assigned by Mask assignment method in Mimis FEA.Then the finite element models were analyzed in AnsysWorkbench19.0.The von-Mises stress distribution and max values of the Cannulated Screws as well as proximal surface of fracture were evaluated,the same for the displacement of the fixation.Results: 1.The distribution and peak values of von-Mises stress for the CS was displaced in the tunnel of CS below the fracture ends as: 39.447 Mpa,40.247 Mpa,43.694 Mpa in the A group,and for the B group,the distribution of stress was uniformed compared with group A,the peak values were located in the tunnels of upper two CS as 21.132 Mpa,22.617 Mpa,25.241 Mpa which were below to group A,being located in the upper surface of the upper CS junctional with the screw tunnel.2.The distribution and peak values of von-Mises stress for the surface of proximal fracture end: the peak values were located in calcar femora of medial femoral neck fracture ends as 10.459 Mpa,12.865 Mpa,14.103 Mpa in group A that were located in the screw tunnel of the fracture surfaces and increasing with the angle.Respectively,6.520 Mpa,8.096 Mpa,7.315 Mpa for Pauwels angulation 50°,60° which was located in the screw tunnel of the fracture surfaces and 70° that was located in the region of calcar femora within the fracture ends in group B.3.Distribution and peak value of displacement of fixation: the max values were located in the top area of femoral head for group A as: 0.7183 mm,0.8926 mm,1.2892 mm and group B as: 0.5168 mm,0.6873 mm,0.8516 mm that below to the group A obviously.Conclusion: The finite element analysis shows that under gravity load,the medial support plate can effectively resist the shear action of the femoral neck fracture ends,reconstruct the medial bone support of the femoral calcar,and transform the shear stress of the fracture ends into the medial compressive stress of the femoral calcar.Thus,the stress peak value of cannulated screws and the peak displacement of femur head can be effectively reduced,and thus the risk of complications such as cannulated screws breaking,femoral head cutting and varus deformity of femoral head can be reduced to a certain extent. |
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