| BackgroundsAnterior instrumentation surgery had been a good choice of treatment for the thoracolumbar and lumbar AIS,because anterior procedures may give greater correction through a direct manipulation of the vertebral body and good coronal correction and apical derotation can be obtained. Furthermore, anterior correction has the potential advantage of preserving additional motion segments by instrumentation of fewer vertebrae.However, complications such as high pseudarthrosis rate and implant failure still have not been resolved.. With the rapid development of internal fixators and 3D correction theory, posterior segmental pedicle screw instrumentation have been widely used in the surgical treatment of thoracolumbar and lumbar AIS. Compared to hook or wire approach, the pedicle screws get a grip with 3-column purchase and offers an enhanced 3-dimensional deformity correction and preservation of motion segments by reducing the extent of fusion. Excellent Correction of thoracolumbar and lumbar AIS was achieved with Segmental pedicle screw instrumentation. For the discussions above, issues of surgical approaches, extent of fusion level of thoracolumbar and lumbar AIS still have been the subject of some debate so far.As a new technique of digital simulation, finite element method has been a hot topic of scoliosis biomechanics recently. Finite element simulation of correction procedure had been focused on posterior CD surgery, few simulation of anterior correction or comparison of posterior and anterior correction was reported.Objectives Using a series of Related CAE software, To develop three dimensional finite element models of the Lenke5 Adolescent Idiopathic scoliotic spine based on quantitative computed tomography scans. After parameters optimization and Validation, the three-dimensional finite element model was used to simulate anterior and posterior correction, investigate the corrective effect of different surgical protocols, and analyse biomechanical stress and strain of the scoliotic spine.Methods1. Development of the three dimensional Finite element model Obtain CT digital data from T1 to caudal end of a female Lenke5 AIS Patient in the supine position.ImPort The CT digital information into the computer software Mimics, and rebuild a 3-Dimension simulation model with surface mesh by the following steps:orientation, division, erase, draw, erode, dilate, boolen operation, define Polyline,remesh. ImPort the simulation model into the computer software HyperMesh 8.0.Remesh the model From surface mesh into body mesh. Define the surface on different vertebrae, ribs and intervertebral discs. Refer to the literature, present the spine with relative material parameters and append the parenchyma such as ligaments and disc.2. Parameters optimization and model validation For parameter optimization, the Emodule of the intervertebral disks and the thickness of the cortices wer emodified based on the clinical bending test. Orthogonal experiment designed by the computer software SPSS is performed and nine groups of experiment plans with three levels and four factors, L 9(34) are adopted to optimize experimental factors. Then data from orthogonal test was treated by Intuitive analysis. For model validation, geometric shape was compared between supine X-ray films and finite element simulation. Bending test and Erect test were simulated. Different segments were extracted from the whole finite element model, and were respectively constrained and loaded referring to historical specimen biomechanical in vitro studies.3. Simulation of corrective surgery of different surgical protocols The finite element model of internal fixation devices was developed According to different surgical approach and fusion level, we designed and simulated four surgical strategy with the model of scoliosis. All the main steps including derotation and compression of each strategy were simulated. The stress variation of the spine, different vertebral displacement, as well as rotation and angle changes were compared among the protocols of different surgical approach and fusion level. Results1 A Three-dimensional Finite Element Model of the Lenke5 Adolescent Idiopathic scoliotic spine including T1—T12, L1—L5 and sacrum has been developed based on quantitative computed tomography scans. Using 4 mesh types and 14 kinds of material parameters, the model consists of 170784 nodes,633668 tetrahedron elements,126636 shell elements,680 cable elements and 132 rod elements. The three dimensional Finite Element Model of the scoliotic spine showed good geometric similarity with supine X-ray.2 Biomachanical bahaviour in simulating Bending test and Erect test was consistentwith clinical practice. The segment simulation results of subsection validation were similar to their references respectively.3 Coronary lumbar deformity was corrected to 22°,23°,26°and 26°espectively for all four surgical protocols used in the simulation., physiological saggital configuration was maintained, but higher stress in the anterior short fusion group. A similar apical rotational correction was recorded,41.68°nd 37.79°, between anterior single-rod corrction and posterior segmental pedicle screw fixation when instrumented to the lower end vertabra. Conclusions1 Based on CT images, the three-dimensional finite element model of Lenke5 idiopathic scoliosis were well established and validated2 The validity of the optimized finite element model was verified successfully, so it was proved to be able to represent the biomechanical behaviour of the actual scoliotic spine.3 The model was successfully used to simulate correction procedures including 90°derotation and compression for the first time. Finite element method may provide theoretical basis and guidance for the operation planning and efficacy evaluation.4 Simulation of all four surgical protocols obtained excellent correction, but short segment fusion maybe not a good choice because of higher stress. Similar correction can be achieved with segmental pedicle screw fixation compared to anterior single-rod corrction when instrumented to the lower vertabra.
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