Relevant Biomechanical Finite Element Analysis Of Posterior Placement Of The Spine

Objective(1)To establish a finite element model of thoracolumbar spine fractures(lumbar 1vertebral fractures,T12-L2 model)for clinical study.(2)To establish a finite element model of vertebral body fractures with screw pedicle screw.(3)To investigate the biomechanical changes of pedicle screws implanted at different sagittal angles and their effects on spinal stability.(4)To explore the possible risk of nail breakage after pedicle screw implantation at different angles in sagittal plane.Materials and Methods(1)Subjects: Three patients admitted to the First Affiliated Hospital of Chengdu Medical College for orthopedics were diagnosed as vertebral compression fractures of the lumbar vertebrae,aged 25-45 years.MRI of lumbar spine was diagnosed as fresh vertebral fractures and exclusion phase Adjacent segment vertebral fractures and other spinal diseases.(2)Data collection: Siemens 64-slice CT was selected to perform thoracolumbar scan and image processing on 3 volunteers.Scanning range: chest 11 vertebral body to sacral 1 whole segment.Select 300 clear bone image window import U disk backup DICOM format,import Mimics image data processing.(3)To establish thoracic-lumbar 2 vertebral body model: The CT data were imported into Mimics,and a preliminary model was established by using threshold segmentation and regional growth.Smooth the model with Geomagic Studio software.Mesh model with HyperMesh and digitized pedicle screw using SoliderWork.(4)Using HyperMesh screws to establish L1 fracture in the sagittal plane at three different angles of nailing model:(1)parallel endplate nail model(2)inclined 7 ° nail model(3)inclined 7 ° nail model;(5)Abaqus software was used to apply various loads to the three groups of models respectively,and biomechanical analysis was conducted on the stress conditions of the three groups.The statistical data were charted and analyzed.ResultsFrom the displacement of vertebral body under different implantations of pedicle screws,we know that the maximal displacement of vertebral body after 3 kinds ofimplanting methods in vertical state appears on the surface of thoracic vertebral body.In torsion,the maximal vertebral body Displacement was moved back to the upper posterior vertebral column and the upper part of the connecting rod;flexion state,the maximum displacement of the vertebral body appears in the front of the thoracic or posterior column of the thoracic 12.In the extension state,the maximum displacement of the vertebral body Concentrated in the chest 12 vertebral body part of the posterior column;lateral curvature state,the greater displacement of the vertebral body mainly concentrated in the chest side of the lateral curvature of the vertebral body.In the internal fixation device stress cloud chart,we observed and calculated that: under the three kinds of nailing methods,the stress concentration place of the internal fixation device is in the near rod section of the screw in all states;under the different working conditions,The stress of the screw in the group was the largest,and the three groups were statistically significant(P <0.05).The stress of the model internal fixation device in the oblique direction was even more serious.In the vertical state,The stress of the internal fixator was the smallest,which was even higher in the parallel nailing group(P<0.05).ConclusionIn this study,three-dimensional nonlinear finite element model was used to simulate the thoracolumbar vertebral fractures through the posterior vertebral body:(1)parallel to the end plate(2)oblique 7 ° nailing(3)inclined 7 ° nailing three models,The biomechanical differences of the three methods were analyzed by comparing the displacement differences of the three models in vertical,flexion,extension,scoliosis and torsion and the maximum stress of pedicle screws.1.Digitized part of the pedicle screw thread can simulate the actual stress of the screw better,and the digital part of the thread can better avoid the conflict between the later gridding and the finite element calculation.This is also an improvement experiment in this study;2.Stabilizing the vertebral body at an angle of 7° obliquely will achieve better stability;3.The incidence of pedicle screws breaking at an angle of 7° obliquely is lower than that of the other two groups.Clinical application should be actively adopted.