Simulation Of Posterior Surgical Correction And Corrective Force Analysis In Idiopathic Scoliosis Using Finite Element Method

In this study, computer aid engineering (CAE) soft was used to establish finite element model(FEM) of the lumbar function spinal unite (FSU), and compared three different models under several behaviour of the FSU to find out the best modeling method. Then use the optimized modeling method to construct six FEMs of the adolescent idiopathic scoliosis (AIS) and validated the final model. On the basis, we simulated the main steps of the posterior correction surgery using the FEMs and An inverse method based on Finite Element Analysis was used to apply forces to the implant screw model such that it was deformed the same after surgery. Then compared the effective of the Key-segmental instrumentation techniques and all segmental pedicle screws strategy.Chapter One Influence of Element Type and Geometry on the Biomechanical Behavior of a Functional Spinal UnitObjective The CAE soft was used to construct3a functional spinal unit (FSU) L4-L5using a specimen-specific finite element model. The aim of this study was to determine the better element type for each anatomical structure.Methods A female adolescent idiopathic scoliosis patient was includes as object of the study. CT imagines of the L4-L5were imported into MIMICS10.01to create the FEMs.3different types of FEMS was performed using reported in vitro data on the mechanical response of an intact lumbar functional unit and its successive reduced stages after the dissection of ligaments, facet joints, vertebral arch and nucleus pulposus. The loading conditions in the study were pure moments in flexion, extension, lateral bending and axial rotation.Results An intact lumbar functional unit was built successfully in three different modeling methods which named model A, B and C. All of the models were subjected to pure moments and forces in the three anatomical planes. For each of the loading scenarios, with and without vertical and follower preload, the presented model A provides results in closest agreement with the most accepted literature. Conclusions Tetrahedron element to build the vertebrae and hexahedral element to create the intervertebral disk was the best modeling method.Chapter Two Establishment and Validation Study of Finite Element Model of Adolescent Idiopathic ScoliosisObjective To build three-dimensional finite element model of adolescent idiopathic scoliosis and to validate the model.Methods In this study, a patient with adolescent idiopathic scoliosis was included as a volunteer. CT transverse scanning was done in supine position from C7to caudal end, and obtained616CT Dicom images. All CT images were imported into Mimics10.01to form qualified three-dimensional geometry model after geometry clean, initial division of shell, mesh partition and assignment of material parameters. To verify the validity of the model, the view of the model ande linieal X-ray films were being compared, and spinal segments (TI0-T11, T11-L1and L1-S1) extracted from the whole finite element model were constrained and loaded respectively referring to historical specimen biomechanical in vitro studies. Compare the results of simulation of the model with the hanging posterior-anterior X-ray, lateral flexion X-ray and fulcrum bending X-ray. Comparing the vertical distance between each barycenter and CSVL of model and X-ray for biomechanical validation.Results A finite element model of Lenkel1BN adolescent idiopathic scoliosis was built, using five mesh types and14kinds of material parameters, in consist of214429nodes,7778combin element,259226shell elements,749910tetrahedron elements and hexahedron elements. The segmental simulations were similar to their references respectively. Though the parameter comparing, we got the individual FEM whose simulation results had no significant statistical difference to the dates of clinical radiographic film (P>0.05).Conclusions The finite element model was built and well validated by geometry appearance, segmental validation and hanging test, lateral bending test, and fulcrum bending test validation which provided an effective way for further biomechanical research. Chapter Three Finite Element Model Simulation of Posterior Surgical Correction of Adolescent Idiopathic Scoliosis and Analysis of Corrective Force of the ImplantObjective Using the method stated above to create six FEMs of adolescent idiopathic scoliosis, and to simulate posterior correction surgery and investigate the corrective force of the pedicle screw.Methods Six FEMs were built to simulate the posterior correction surgery with all-segmental instrumentation strategy. Then the corrective force of each screw was analysised by CAE soft.Results Six FEMs successfully completed the simulation of posterior correction surgery. The upper instrumentation vertebra was selected to T4in all of the FEMs, and the lowest instrumentation vertebra was to L3in2models, L2in3models and L1in one model. The mean Cobb’s angles of proximal curve, main thoracic curve, lumbar cure, T5-12sagittal kyphosis and L1-5lordosis pro-correction and post-correction simulation were22.8°to8,41.6°to10°,28.5°to8.5°,19.7°to21.8°,34.3°to32.8°, respectively. The corrective force located at the convex and the end instrumentation segment were significant greater than the rest concave area.Conclusions The FEMs can effectively simulate the correction procedure and provide a new way to optimize the fixation strategy by corrective force analysis.Chapter Four Application of Finite element analysis of corrective force in the determination of Key-segment for Surgical Correction of Adolescent Idiopathic ScoliosisObjective To investigate the effective of finite element analysis of corrective force in the determination of Key-segment for surgical correction of adolescent idiopathic scoliosis.Methods Wipe out the pedicle screw which force under lGpa thought the finite element analysis and recreate six FEMs with Key-segment fixation. Simulated the posterior surgical correction again with the secondary finite element models. Measured the Cobb angles and compare the parameter with postoperative X-ray.Results The correction rate of the Key-segment fixation strategy has no significant difference with the all-segment instrumentation strategy, and there was no significant difference when compare to the practical postoperative X-ray. The mount of implants were less than the clinical date.Conclusions The finite element analysis is an effective method in determination of Key-segmental instrumentation. In the future, it can offer an essential guide to assist surgeons during preoperative planning of surgical instrumentation in adolescent idiopathic scoliosis.