| In current study, we established, validated and optimized a complete three-dimensional finite element model of adult degenerative scoliosis based on the individual CT images, by using computer aided engineering (CAE) softwares. On the basis of above, we simulated posterior three-dimensional correction surgery using this finite element model to investigate correction effectiveness with different upper instrumented vertebra (UIV) and lowest instrumented vertebra (LIV).Objective Using CAE softwares, to build three-dimensional finite element model of adult degenerative scoliosis based on the individual CT images.Methods A 61-year-old female adult degenerative 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 522 CT dicom images. All CT images were imported into Mimics 10.01 to form qualified three-dimensional geometric model after geometry clean, including all thoraco-lumbar-sacral vertebrae and thoracic cage, which was further delivered to HypherMesh 8.0 to build 3D finite element model by mesh partition and quality control. A variety of material parameters were given to different mesh according to references.Results A complete three-dimensional finite element model of adult degenerative scoliosis was built successfully, including all thoraco- lumbar-sacral spine and thoracic cage, using 4 mesh types and 14 kinds of material parameters, in consist of 136398 nodes,509819 tetrahedron elements,95835 shell elements,680 cable elements and 132 rod elements.Conclusions A complete three-dimensional finite element model of adult degenerative scoliosis in details, was built successfully based on individual CT images.Objective To validate the 3D finite element model of adult degenerative scoliosis built in chapter one, by contrast with in-vitro studies and the X-ray film.Methods (1) The 3D finite element model contrasted with supine X-ray film to investigate the geometrical similarity (2) Subsection validation:Segment T1-T4, T5-T8, T9-T12 and T1-L1 were extracted from the whole finite element model, and the four segments were respectively constrained and loaded referring to historical specimen biomechanical in-vitro studies.Results (1) The finite element model and supine X-ray film had very good consistency, not only in the position of the center of vertebral body, but also in the sagittal and coronal plane. (2) The segment simulation results were similar to their references respectively.Conclusions The three-dimensional finite element model of adult degenerative scoliosis were well validated by geometric appearance and segment validation, which was qualified for further biomechanical simulation study. Objective To personalize the geometric appearance of the finite element model and the material properties by parameter optimization.Methods (1) Simulation of the Left and right Bending test:made the upper and lower end vertebral of the finite element model coincide with the clinical trial, then compared the vertebral sequence and the Cobb angle. (2) Using the orthogonal experimental design analysis of three factors and three levels of intervertebral disc material property to optimize the parameters, and then achieve the biomechanical property of the individual. (3) Using the optimized model to simulate Left and right Bending test and Erect-supine test, then contrasted with the clinical results.Results For this patient, the material properties of lumbar disc had the biggest influence on spinal flexibility. When the parameters of the disc material properties of thoracic curve, lumbar curve and lower lumbar curve were respectively 8,0.2 and 1, the results of computer simulation were closest to the real conditions. After optimization, the biomechanical behavior of the finite element model and the actual clinical outcomes had better consistency.Conclusions Through the optimization of the parameters, the simulation features of the model was significantly improved. It was qualified for further biomechanical simulation study of the scoliosis surgery. Objective To simulate posterior correction surgery using the finite element model of adult degenerative scoliosis. Compare the differences between several pedicle screw placement strategies, to investigate correction effectiveness with different upper instrumented vertebra (UIV) and lowest instrumented vertebra (LIV).Methods Established the 3D finite element model of screws and rods. A numerical study was conducted by simulating the CD surgery and quantifying the biomechanical changes of intraoperative correction. An automated algorithm simulated all the main steps of the CD surgery. For each step, vertebral kinematics was exported, especially the stress variation of pedicle screw, as well as the displacement of vertebral body, to fully understand the complexity of three-dimensional correction. According to the clinical reports of proximal and distal fusion strategy, we compared several screw placement strategies using computer simulation program based on the finite element model. Comparison of vertebral displacement, rotation, angle changes and the stress variation of pedicle screws, it could help to optimize the surgical treatment.Results (1) In this study, we simulated the 90°rotation operation for the patient with scoliosis and kyphosis, explored a finite element simulating method of correction from the convex side for adult degenerative lumbar scoliosis. (2) There was no significant difference in the correction of Cobb angle and lumbar lordosis between the four orthopedic strategies. Compared with fusion to L1, fusion to T10 was more powerful to correct the scoliosis towards the center line, had stronger ability of derotation, and the segments between fusion and non-fusion had a better transition in the strategy of fusion to T10. Compared with fusion to L5, the lowest screw stress of fusion to S1 was much higher, while the L5/S1 intervertebral disc stress was lower.Conclusion (1) Simulate the derotation maneuver in the finite element model of adult degenerative scoliosis. Build a new and personalized finite element analysis platform for scoliosis. (2) For the adult degenerative scoliosis patients with small Cobb angle, good spinal balance and good flexibility, short segment fusion can also achieve satisfactory results. |
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