| In this study, computer aided engineering (CAE) software was used to establish a complete three-dimensional finite element model of Lenke 6 idiopathic scoliosis based on CT images, including all thoraco-lumbar-sacral vertebrae and thoracic cage. Then optimized the model parameters and validated the final model. On the basis, we simulated all the main steps of posterior Cotrel-Dubousset (CD) technique correction surgery using this IS finite element model. Then simulated different correction strategy to explore the effect of key-segment instrumentation technique and selective fusion strategy.Objective The CAE softwares was used to build three-dimensional finite element model of Lenke 6 idiopathic scoliosis based on CT images.Methods A 14-year-old female Lenke 6 idiopathic scoliosis patient was included as volunteer for current study. CT transverse scanning in supine position was done from T1 to caudal end in lmm layer interval, to obtain 511 CT dicom images. All CT images were imported into Mimics 10.01 to form qualified IS three-dimensional geometric model after geometry clean, including all thoraco-lumbar-sacral vertebrae and thoracic cage, which was further delivered to HypherMesh 7.0 to build 3d finite element IS model by mesh partition and quality control. A variety of material parameters were given to different mesh according to references.Results A three-dimensional finite element model of Lenke 6 idiopathic scoliosis was built successfully, including all thoraco-lumbar-sacral spine and thoracic cage, using 4 mesh types and 13 kinds of material parameters, in consist of 208739 nodes,758197 tetrahedron elements,90776 shell elements,680 cable elements and 138 rod elements.Conclusions A three-dimensional finite element model of Lenke 6 IS in details, was built successfully based on CT transverse scanning images.Objective To personalized the mechanical properties of finite element model of Lenke 6 IS 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 four factors and three levels of disc material property to optimize the parameters, and then achieve the biomechanical property of the individual.Compared the model with upstanding posterior-anterior X-Ray, supine posterior-anterior X-Ray and lateral flexion X-Ray of supine posterior-anterior position. Chose T1-T4 and L4-S1 to compare with related results of biomechanics empirical study.Results Orthogonal experiment results showed that the best combinations, which mimimized the difference of model and the actual, were dise property in the proximal thoracic segments is 0.2, the main thoracic segments is 1, the thoracolumbar segments is 1, and the lower lumbar segments is 8.Compared the Cobb angles of optimized model and actual X-ray film, the largest difference was 2.5°, and the mibimum is 0. Compared the center of mass deviated from sacral middle line between X-Ray and optimized model, P>0.10, which considered no differences between them. Chose T1-T4 and L4-S1 to compare with related results of biomechanics empirical study, the rotation of the model was in the boundary of related results.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. The optimized three-dimensional finite element model of Lenke 6 idiopathic scoliosis was well validated by geometry appearance, left and right supine bending test, standing-spuine test and segment validation, which was qualified for further biomechanical simulation study.Objective To simulate posterior CD correction surgery using the optimized finite element model step by step.Methods Established the pedicle screws and rods finite element model. Simulated posterior release by removing the interspinous ligaments, supraspinous ligaments and joint capsule of instrumented segments. Anatomically implanted the pedicle screws into the sconliosis model. Generated the correctted rod in the left side. Given the rod displacement of X, Y direction to shape the prupose correctted rod. Generated handles and rotated the rod 90°, which translated the coronal scoliosis into sagittal kyphosis and lordosis. Then placed the stable rod. Turned the screws to move closer to the rod. Locked the joint activity of screw-rod, released the stress.Results Successfully completed each step simulation of CD correction technique. After correction the Cobb angle of thoracolumbar curve was 29.2°with the 47.8% correction rate, and the Cobb angle of the main thoracic curve was 24.4°with the 43.9% correction rate. The alignment of the spine was improved.Conclusion It was the first time to completely simulate all main steps of Cotrel-Dubousset (CD) surgery in the finite element model of Lenke 6 scoliosis. This could help to evaluation, prediction and even optimize the surgical plan and provide a theoretical support.Objective To explore the feasibility and effect of key-segment instrumentation and the suitability of selective fusion strategy for Lenke 6 scoliosis by finite element analysis.Methods Simulated the following conditions:all-segment pedicle screw instrumentation surgery, key-segment pedicle screw instrumentation surgery, selective thoracolumbar curve fusion surgery. Measured the curve Cobb angles and calculated the correction rate in all above conditions. Analyzed the correctted effect of these conditions.Results The correction rates of thoracolumbar curve and main thoracic curve were:47.8% and 43.9% in all-segment pedicle screw instrumentation surgery (non-selective fusion),44.2% and 19.1% in key-segment pedicle screw instrumentation surgery,43.5% and 14.3% in selective thoracolumbar curve fusion surgery. Conclusions The effect of all-segment pedicle screw instrumentation surgery was better than key-segment pedicle screw instrumentation surgery for the more force placements. Non-selective fusion, which could correct the two curve and improve the alignment significantly, was more suitable for Lenke 6 scoliosis. |
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