Finite Element Simulation Of CBT Fixation Technique For The Correction Of Scoliosis Under The Gravity Environment

Analog Simulation of lumbar scoliosis used the Cortical Bone Trajectory fixation technology to achieve correction and this thesis proposes a simple and effective method to establish a three-dimensional(3D)entity model,which applied the finite element analysis method to calculate the length and diameter of the screw in CBT fixation from the perspective of biomechanics,thus predicting the process and results of scoliosis surgery theoretically,reducing the trauma to the patients due to the screw is too long or the diameter is too large as well as avoiding the loosen screw leads to the failure of the surgery.This thesis established the L4,L5 lumbar vertebrae in Mimics by using the CT images,and also the intervertebral disc D45 was built,along with all the models were optimized.In Solidworks,9 sets of different sizes of screws were established by comparing with the real pedicle screws,and all the models were optimized in 3-matic and 3D solid model was generated.In Mimics,the simulation surgery inserted the screw and then fixed and connected the same side of the screw according to the CBT fixation technique.Using the Ansys simulation calculated the pull-out strength of the screw,the stress of the human body standing in the gravity environment as well as the load condition upon the lumbar and intervertebral disc,the stress of the screw,the fixation strength of the CBT fixation technique to the lumbar vertebrae,and analyzed the results to get the screw which was suitable for the lumbar model.In this thesis,we use the 3D model lattice to control the length of the triangular slice;the finite element analysis is put into practice in Mimics and 3-matic software,which can carry out very real simulation analysis on the vertebral body,intervertebral disc and screws.The method owns the advantages of simple operation,high quality of simulation model as well as the high calculation speed,the method proposed in this thesis can be used for finite element analysis of different spine according to CBT technique fixation requirements.The result shows that the vertebral body interacts with the screw under the gravity;the stress of the vertebral body is 5 to 6 times of that on the intervertebral disc.The stress is concentrated in front of the vertebral body.Increasing the length and diameter of the screw would reduce the stress of the screw;As a result,the stress of the screw is negatively correlated with the length and diameter of the screw and the pull-out force of the screw and the lumbar fixation strength are positively correlated with the length and diameter of the screw.The simulation analysis data of axial compression,extension,lateral flexion and torsion suggest that the length of the screw changed from 30mm to 35mm,its stability increased by 7%,10%,2%,10%;While the length of the screw changed from 35mm to 40mm,the stability were increased by 2%,3%,1%,1%.When the diameter of the screw changes from 4mm to 5mm,accordingly the stability increases by 29%,24%,2%and 24%.However,the diameter of the screw changes from 5mm to 6mm,the stability increases by 6%,18%,1%and 3%respectively.The analysis result is that the appropriate screw length used in lumbar CBT fixation correction is 35mm,the diameter is between 5mm and 6mm.