Finite Element Analysis Of Hemivertebrae Resection Of Different Posterior Segmental Fixation Three-dimensional Correction Of Infant Congential Scoliosis

Objective:Congenital scoliosis is a kind of disease that occurs in children with severe spinal deformity, after the incidence of idiopathic scoliosis;According to foreign epidemiological statistics,the prevalence rate is about 0.5-1% when the baby was born, but its pathogenesis is not very clear. During to the great influence of congenital scoliosis on children’s physical and mental health, such as thoracic malformations, cardiac and pulmonary dysfunction, so the disease often needs early intervention treatment. The Common treatment methods include conservative treatment and operation treatment. The three-dimensional finite element model of congenital scoliosis caused by thoracolumbar hemivertebrae is constructed, that based on the patient’s CT scanning. The research is used to simulate the posterior surgical correction, that concluds hemivertebra resection and Pedicle screw, titanium rod internal fixation system, by comparing the orthopedic effect of different fixed segment and biomechanical characteristics of the section, as to provide theoretical basis for the choice of clinical treatment, and further optimize the operation scheme.Methods:1 Choose the object of research and acquired CT images:The child of congential scoliosis caused by hemivertebrae was selected in the research, who was male,2 years old 9 months,weight 14 ㎏,height 90 ㎝.The 12 thoracic was hemivertebrae. Siemens 64-slice CT transverse scanning of the patient was done from the second cervical vertebra to the sacrum in supine position, thickness was 1.25 mm and interlayer spacing was 0mm, the main content of scanning were all bony structure and intervertebral discs.We obtain 470 CT dicom images and 240 pictures of effective part in the middle were used to construct the model.2 The establishment of the primary 3D model: The Dicom format images obtained were imported into thereverse engineering software Mimics 14, the thoracic and lumbar of primary 3D model were built by masking, filling, deleting, smoothing et. Compared the positive side view of the model with clinical positive lateral X ray film, the hemivertebrae position and lateral bending angle were basically identical. In the Geomagic Studio 12, we constructed the posterior longitudinal ligament, supraspinous ligament, interspinal ligament,yellow ligament, intervertebral disc and growth plate. The pedicle screws and titanium bars were generated in Creo 2.0.3 Establish the three-dimensional finite element model: In the software of Mimics 14, the body of primary model was generated, and the vertebrae, intervertebral discs, the growth plate, ligaments and internal fixation system were imported in the 3-Matic5.1 software, meshing the model respectively, to obtain a three-dimensional finite element model of congenital scoliosis in.4 Simulation of posterior approach orthopaedic operation:In 3-matic 5.1,we simulated the posterior hemivertebra resection and andpedicle screw internal fixation operation.During the operation, we achieved the scoliosis deformity correction, through resecting the peripheral related ligaments, placing the pedicle screws, removing the hemivertebrae and deformity of intervertebral disc, installing orthopaedic titanium rod and gradually closing T11 and L1 intervertebral space.5 Finite element analysis:The congenital scoliosis finite element model was imported to ANSYS 13.0, and we got the equivalent stress nephogram of different fixed segment,by constraining, loading respectively and solving the model, and further to compare changes of stress.Results:1 Based on CT images,the individual finite element model of congenital scoliosis caused by hemivertebrae has been successfully established through the relevant computer aided engineering software. The model has better described the basic characteristics of children spine, concluding thoracic, lumbar,intervertebral disc,growth plate,ligament,vertebral pedicle screw, titanium bar.There were totally 187634 modules and 266453 nodes.2 The posterior three-dimensional orthopaedic operation simulation was successfully completed.According to the difference of fixed segment, it was divided into four groups, and concave and convex side in the orthopedic of every group were respectively inserted into a pedicle screw, namely A group(T11~L1, a total of 4 screws), group B(T11~L2, a total of 6 screws), group C(T10~L1, a total of 6 screws), group D(T10~L2, a total of 8 screws).3 Application of software ANSYS13.0 analysis showed that four groups of fixing scheme under the model of equivalent stress nephogram and posterior convex angle measurement technique.Equivalent stress nephograms indicated that the maximum equivalent stress was mainly concentrated at the junction of pedicle screw nail cap and a screw body, nail cap and orthopedic rod,screws and vertebral pedicle.The posterior lobe showed that the A group is the largest angle,when extending to both sides of the fixed segment,scoliosis angle decreases,further extending section,angle had no significant change.4 Analysising results showed that the stress of vertebral pedicle screw was maximum in T11,L1 of the convex side, the stress of both ends was significantly smaller than T11,L1.In the concave side,the stress in T11,LI was smaller than the convex side.In the four groups of orthopedic scheme,the stress of pedicle screws was maximum in group A,when extending to the ends of a fixed segment, the stress reduced,such as the B group and C group.But further extending a fixed segment,no obvious effects happened on the screw stress,such as the D group.Conclusion:1 The application of computer aided engineering software, based on CT scan images of volunteers,built a three-dimensional finite element model of individual children semi vertebral caused by congenital scoliosis successfully.2 The model has been used to simulate congenital scoliosis posterior hemivertebrae resection operation of different fixed segment three dimensional correction successfully,simulation results of the patient individualized operation showed that posterior short segment fixation was the better treatment plan.3 A variety of additional stresses could be seted on the model, and the correlation analysis and simulation of operation research were made in order to provide the theory basis of the biomechanics for clinical personalized operation scheme, the introduction of growth plate may be helpful for doctors to analyze the development of deformity and predict the rectification process and the effect.