Finite Element Model Construction And Surgical Correction Biomechanical Study Of Adolescent Idiopathic Scoliosis With Pelvic Imbalance

In this study, computer aided engineering (CAE) soft ware was used to establish two complete three-dimensional finite element models of idiopathic scoliosis with pelvic imbalance based on CT images, including all thoraco-lumbar-sacral vertebrae and thoracic cage. Then optimized two models parameters and validated the final models. On the basis, we simulated all main steps of posterior Cotrel-Dubousset (CD) technique correction surgery using these two IS finite element models. We simulated different correction strategies to explore the effect of investigating correction effectiveness with different lowest instrumented vertebra.Chapter One. Establishment of Three-dimensional Finite Element Models of Idiopathic Scoliosis with Pelvic ImbalanceObjective The CAE software was used to build three-dimensional finite element models of idiopathic scoliosis with pelvic imbalance based on CT images.Methods A17-year-old male and a15-year-old male idiopathic scoliosis patients were included as volunieer for current study. CT transverse scanning in supine position was done from T1to caudal end in lmm layer interval, to obtain539and549CT dicom images. All CT images were imported into Mimics10.01to form qualified IS three-dimensional geometric model after geometry clean, including all thoraco-lumbar-sacral vertebrae and thoracic cage, which was further delivered to HypherMesh10.0to build3D finite element IS model by mesh partition and quality control. A variety of material parameters were given to different mesh according to references.Results Two three-dimensional finite element models of idiopathic scoliosis with pelvic imbalance were built successfully, including all thoraco-lumbar-sacral spine and thoracic cage, using5mesh types and14kinds of material parameters, in consist of197195nodes,9633hexahedron elements,578031tetrahedron elements,228273shell elements,5239cable elements and1441rod elements in patient A model. Patient B model included219162nodes,10559hexahedron elements,601982tetrahedron elements,2330646shell elements,6528cable elements and1320rod elementsConclusions Two three-dimensional finite element models of IS with pelvic imbalance in details, were built successfully based on CT transverse scanning images. Chapter Two. Personalization of the mechanical property and validation of optimized finite element modelObjective To personalized the mechanical properties of finite element models of IS with pelvic imbalance built in chapter one, verify the validity of the optimized model.Methods The personalization of the mechanical properties is done using the flexible tests routinely done prior to the surgery-based on preoperative stereoradiography and flexibility test radiographs. And using the orthogonal experimental design analysis of three factors and three levels of disc material property to optimize the parameters, and then achieve the biomechanical property of the individual. Compared the models with standing posterior-anterior X-ray, overhang posterior-anterior X-ray and lateral flexion X-ray of supine posterior-anterior position. Chose T7-T11、T11-L1and L1-S1to compare with related results of biomechanics empirical study.Results Orthogonal experiment results showed that the best combinations, which minimized the difference of model and the actual, were dise property in the proximal thoracic segments is0.2, the thoracolumbar segments is1, and the lower lumbar segments is8. The activity of the two three-dimensional finite element models is smaller than the normal lumbar. Intervertebral disc stress distribution tended to intervertebral disc around, extension movement each intervertebral disc stress is maximum, apex vertebral prone to stress concentration, the extension under the condition of facet joint stress concentration of the obviously, especially in the facet joint effect of scoliosis vertex segment of the maximum.Conclusions The way using orthogonal experimental design analysis to optimize the parameters was feasible and necessary. The optimized model was more in line with the actual.Chapter Three. Three-dimensional Finite Element Simulation of Posterior Surgical Correction of idiopathic scoiliosis with pelvic imbalanceObjective To simulate posterior correction surgery using finite element models of IS with pelvic imbalance and investigate correction effectiveness with different lowest instrumented vertebra (LIV).Methods Posterior pedicle screws on concave side and pre-bent rod placed were placed on IS finite element models, constraints and loadings were applied at the same time as follows:sacrum constrained horizontally, corresponding downward forces applied to every segment for gravity and muscle actions according to references,10Nm torsion moment against convex applied to apical zone, and proper torsion moment applied to rod to rotate90degrees backward. The upper instrumented vertebra (UIV), was selected to T10and LIV down to L4, L5, S1in patient A.;The upper instrumented vertebra (UIV), was selected to T7and LIV still down to L4, L5, S1in patient B, with comparison of correction effect nesses among the three LIV choices in each patient.Results Coronary lumbar deformity was corrected to25°、23°、20°or all three surgical protocols used in the simulation in patient A. Coronary lumbar deformity was corrected to29°、24°21°or all three surgical protocols used in the simulation in patient B. Physiological saggital configuration was maintained. Correction rates were significantly different among the three LIV choices.Conclusions3-D finite element simulation on the successful implementation of the posterior operation of90°rotation operation and distraction correction process of compressing. Finite element simulation provides sufficient theoretical basis and accurate operation platform for the evaluation of idiopathic scoliosis with pelvic imbalance correction optimization operation scheme and effect of treatment of scoliosis; in this study, two cases of three-dimensional finite element model of the recovery rate, spinal appearance by orthopedic operation after the straight, but there are also problems too large stress appeared the fusion segment to S1, we need to simulate the protection of S1screw scheme, the appropriate loading constraints, this is the need for further study, the problems to be solved; The best solution scheme of two in patient A and scheme of C in patient B with scheme for three-dimensional finite element model of the corresponding simulation after orthopedic operation, the best orthopedic effect and the corresponding vertebral stress than the average, can try short-segment fusion, the segmental motion.