| BackgroundAdolescent idiopathic scoliosis is a complex three-dimensional deformity of the spine structure,including scoliosis in coronal plane,sagittal sequence of abnormal shape and the rotation axis plane.In previous reports up to the spinal deformity correction,the hotspot of research concentrated on the coronal plane deformity correction.However,the recent research revealed that for the sagittal plane deformity correction also plays an important role in spinal deformity correction.Furthermore,the sagittal plane deformity correction showed a closer relation in sagittal balance reconstruction,as well as the health-related life quality for the post-surgery patients.Therefore,an increasing number of researches upon spinal sagittal plane deformity are carried on in recent years.Sagittal balance of the body is about the overall balance,including the spine-pelvis balance.Corresponding compensation occurs when one part runs into imbalance,which increases the load for the body.If breaks the compensatory limitation the body could bear,decompensated and its negative impacts including pain,mobility limitation,or even fracture fixation and other undesirable results would apply on human body.Therefore,reconstruct the sagittal plane parameters by corrective surgeries,and regain the normal physiological sequence after operation are essential for scoliosis treatment.However,the spinal sagittal parameters research at present are mainly clinical cases follow-ups,reports about basic biomechanics are rarely seen.AimsIn this study,a three-dimensional finite element method will be set up,based on the complete collected CT scan data,which will be extracted and processed by computer software.Finally,to build a three-dimensional finite element model to simulate the real spinal column and to verify afterwards.Through simulate the posterior surgeries,to explore the effects of sagittal plane with deformity rods in various materials,as well as the changes of sagittal planes under different prebending radian parameter settings.Meanwhile,through different operation procedures to perform the posterior Ponte osteotomy releasing spinal structure,in purpose to study the sagittal parameters.Furthermore,the changes of sagittal plane in interval pedicle screw will be explored.Methods1.To establish a scoliosis nonlinear three-dimensional finite element model.A 14-year-old female adolescent idiopathic scoliosis patient was included,routine examinations were carried out to rule out other diseases.Slice CT scan,which was ranged from T1 to sacrococcyx with the layer thickness set to 0.8mm,was performed onto the patient.Data was imported to a modeling software Mimics,the spinal finite element model diagram was obtained and extracted by setting various threshold values,followed with modifications and geometry cleanups.Afterwards,according to the anatomical and histological parameters,the appropriate properties were set up.Then the disc,ligament and other tissues were analog reconstructed.In the end,the overall spinal structure model was established,and was compared with parameters of the patient collected prior to surgery,the effectiveness was verified after loading the previous reports.2.To study the curvature of sagittal sequence under the finite element model by using various Elasto-plastic rods and different pre-bent radian correction of scoliosis.On the basis of the spine finite element model established in the first part,the surgical simulations were performed,then were analyzed and calculated by ABAQUS software.Set the pre-bent parameters of the orthopedic rods as below: firstly,set the pre-bent radians of the titanium alloy rods and the analog cobalt cocr rods to 28 °,respectively,which is the physiological curvature of the spine,to explore the changes of the sagittal plane.Secondly,set the pre-bent radians of different titanium alloy rods to 40°,to simulate the parameters changes of spine sagittal plane.3.To analysis the sagittal plane sequence by finite element model applied with the interval screw sets and the Ponte osteotomy.In this part of study,the pre-bent radians of titanium rods were set up to 28 °,and the same boundary conditions were fixed to simulate the surgical orthopedic effects.Screws were intervallic arranged on both sides of the vertebral,exactly the same as the clinical procedures,then to compare the parameters changes of spine sagittal plane.The Ponte osteotomy was carried out on the apical region of the spine,releasing the bone connection in this region and the adjacent ligamentous structures. Furthermore,the bilateral pedicle screw placement was performed,and then the analyzed data was compared to the non-osteotomy group with the parameters of spine sagittal plane.Results1.Established a complete AIS finite element model,which is entirely included the thoracic vertebral structure,sacrum,coccyx,intervertebral discs and ligaments models.Among which,the ligament models are consisted of supraspinal ligament,interspinous ligament,ligamentum flavum,an anterior longitudinal ligament,posterior longitudinal ligament and transverse ligament.The bones were simulated by entity units,the endplates were modeled by shell units,and the ligaments were simulated by imitated ligaments.The model consists of 3 types of units,a total of 691271 units,which are 667459 entity units,62838 shell units and 675 imitated units.By comparing the parameters of the model to the X-ray data of the patients,there was no difference revealed.With the loading experiments performed,similar results were shown.2.In this study,rods in two different materials were used in analog surgeries,which were cobalt chromium rods and titanium rods.Set the pre-bent radian as 28° and same boundary conditions in both groups,cobalt chrome rods thoracic kyphosis sagittal reconstruction return to 25 °,titanium orthopedic rod group 12 °,sagittal displacement between two vertebrae of comparison,P <0.05,statistically significant.In the next experiment,the pre-bent arc of 28° previously was set up as the control group,while the pre-bent radian of the experimental group was set as 40°.By increasing the pre-bent radians,a better orthopedic force and a better spinal sagittal plane deformity reconstruction were revealed.when adjust the sagittal thoracic kyphosis back to 27 °,the screw pullout force was increased,and vertebral sagittal displacement comparison between the two groups was3.In the group of simulation interval pedicle screw placement,scoliosis curvature of the thoracic kyphosis sagittal orthopedic after treatment restored to 11 °,the screw pullout force was increased,and vertebral sagittal displacement was measured and compared with the control group,P> 0.05,no significant difference.In the group of simulation Ponte osteotomy,thoracic kyphosis correction was appealed to be 18 °,the screw pullout force was decreased,and vertebral sagittal displacement was measured and compared with the control group,P<0.05,the difference was statistically significant.Conclusions1.This study based on the data collected from CT scan,in addition of being imported to Mimics software and the followed up data extraction,a complete scoliosis model was established.Meanwhile,the intervertebral disc of the patients was successfully simulated,and the simulation of imitated ligaments model was applied.Furthermore,the model was established with a complete structure,matched geometric parameters,and the precisely subjected grid elements.In addition,the data of selected spine segments was loaded and verified,which demonstrated to be approximated with reported results.Therefore,the newly established model was proven to be effective.2.The cobalt chromium rods and the titanium rods were used in orthopedic surgery simulation with fixed parameters,which illustrated cobalt chromium rods applied a better effect in sagittal plane orthopedic,and the screw pullout force was increased.With increased pre-bent radians in titanium rods,a better sagittal curvature recovery could be achieved.However,the screw pullout force was increased.3.By using the interval pedicle screw placement with titanium in scoliosis treatment,revealed that there was no significant difference in sagittal plane between the interval group and the whole segments pedicle group,but,the screw pullout force was increased.4.With simulation of Ponte osteotomy combined whole segments pedicle screw placement with titanium rods in scoliosis treatment,showed a better effect in the thoracic kyphosis recovery,and the screw pullout force was decreased.The changes of spinal sagittal parameters were found to be statistically significant by compared with the control group. |
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