| Objective In order to optimize the clinical treatment programs of congenital scoliosis caused by hemivertebrae, a individual three-dimensional finite element model was established to simulated three-dimensional correction surgery. Through the simulation, we want to investigate correction effectiveness with different surgical methods and provide a theoretical basis of biomechanical characteristics.Methods A 13-year-old female patient with congenital scoliosis caused by hemivertebrae 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 507 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, then the initial division of shell element mesh was done. The model was further delivered to HypherMesh 8.0 to build a three-dimensional scoliosis finite element model by mesh partition and quality control. A variety of material parameters were given to different mesh according to references. To verify the validity of the model, the view of the model and clinical X-ray films were being compared, and spinal segments (T1-T4, T5-T8, L1-L4, L1-S1) extracted from the whole finite element model were constrained and loaded respectively referring to historical specimen biomechanical in vitro studies. Further to personalize and modify the FE model, orthogonal experimental design and visual analysis was used to choose the most optimized parameter of the model through simulating the clinical bending experiment. Then the individual FE model was applied to simulate hemivertebra resection with different instrumentation strategies, and find out which one is the best for not only satisfying the correction effect but also lowing the risk of screw pullout.Results A three-dimensional finite element model of congenital scoliosis caused by hemivertebrae 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 109936 nodes,411988 tetrahedron elements,87847 shell elements,690 cable elements and 138 rod elements. The model is very similar to the structural characteristics of the patient's spine. The segment simulation results were close to in vitro experimental results with the respective reference, the error was less than 10%. Though the parameter optimization, we got the individual FE model, whose simulation results had no significant statistical difference compared to the dates of clinical practice (P> 0.05). From the simulation of the surgery, we can know that posterior instrumented fusion was better than anterior instrumented fusion after hemivertebrae resection, especially for the kyphosis angle correction, the ratio was all above 50%; and the differences between posterior short-segment fixation and long-segment after hemivertebrae resection were not obviously.Conclusions A three-dimensional individual FE model of congenital scoliosis caused by hemivertebrae in details was built to simulate the surgery of hemivertebrae resection successfully. The material properties of the model were personalized based on the pre-operative side bending X-rays of the patient at first. The surgical simulations showed that posterior short-segment fixation was the best treatment strategy. This finite element modeling and analysis method for the treatment of scoliosis can improve our understanding of surgical biomechanics and provide a theoretical and experimental basis, which can help us predicting the outcome of different surgical strategies. The simulator represents a useful analytical tool to rationalize surgical operations and provide optimal results for a specific patient. In the future, it will offer an essential guide to assist surgeons during preoperative planning of surgical instrumentation of the scoliotic spine.
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