| Objective For the reconstruction of pelvic stability of spine disease to establish the optimal way.The geometric bone channel screw parameters were analyzed by finite element method.Production of guide plate is applied in clinical treatment.Methods CT data of the lumbar-sacral-iliac spine were collected in one healthy Chinese adult,and Mimics20 software was used for 3d reconstruction of the lumbar-sacral-iliac spine model.Then import the Geomagic 12 software for denoising and smoothing.The lumbar sacrum-iliac crest model and related parameters were imported into Solidworks 2015 software for sagittal multilayer subdivision of the iliac wing structure with a thickness of 1mm.The geometric boundary of the iliac crest was determined on each plane.The two-dimensional image coordinates of the geometric boundary point of each iliac crest subdivision plane were extracted to generate the maximum inscribed circle of the boundary.Then,a straight line closest to each central point was fitted by the least square method using mathematical optimization technology.The straight line was regarded as the central axis of the best geometrical lag screw screw passage in the iliac crest.Along the central axis,the geometric nail holes in the iliac crest were generated,and the Angle,maximum length and diameter of the nail passage were confirmed.According to the set of nail,ilium and screw assembly model,screw nail are according to the design way in bilateral bone cortex and breakthrough.The assignment and the grid: on the basis of lumbar vertebral body,intervertebral discs,bilateral iliac and tensile screws of different material properties of four kinds of materials respectively for the assignment,and then for meshing.Assignment and meshing: four materials were assigned to the lumbar vertebral body,intervertebral disc,bilateral iliac crest and lag screw according to their different material properties,and then meshed.Apply loadand constraint: constraint the left and right ends of the ilium,according to the definition of the lumbar iliac anatomy,establish the lumbar-sacral-iliac axis vector,establish the constraint unit.The pressure load was loaded along the top of waist 2 with 400 N axial load and 10 N torque to the coupling unit control node,and the activities in 6 directions of forward extension,backward flexion,left and right lateral flexion and left and right rotation were respectively simulated.Ensure that the load is evenly distributed over the model.Post-processing: import the data into Ansys Workbench 18.0 software,conduct calculation and analysis on it,draw a conclusion and display it with color contours,and finally conduct analysis.Results Experiments including the pedicle screws and iliac bone screw channel geometry,lumbar vertebral bodies(L2-4),the intervertebral disc,the sacrum and ilium and corresponding ligament structure finite element model of healthy adults.There were 583,227 assembly points and 354,330 assembly units,and the force of each segment pedicle screw,iliac geometric bone passage screw,lumbar vertebral body,lumbar intervertebral disc,orthopaedic bar and transverse bar in the six directions of anterior extension,posterior flexion,left and right lateral flexion and left and right rotation were measured.Conclusion First,geometric bone passage screws are proved to be safe and effective from a biomechanical point of view.Second,it can make it easy to deal with complex clinical problems. |
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