Finite Element Analysis Of Cross-link Device’s Evaluation In The Posterior Surgical Correction Of Congenital Scoliosis Caused By Hemivertebra

Objective:In order to provide the basis for the choice of clinical treatment ofwhether to use the Cross-link Device(CLD) in the posterior surgicalcorrection of Congenital Scoliosis(CS) caused by hemivertebrae.Athree-dimensional Finite element model was established to simulated thecorrection posterior surgery of Congenital Scoliosis.The model was basedon an infant congenital scoliosis child which one the T12is ahemivertebra.By loading the force on the model to simulated the spinalbending,later bending and rotation,we analysis the evaluation of CLD inthe correction posterior surgery.Methods：1Choice the study object:Select a child with congential scoliosiscaused by hemivertebrae.The child’s male,2years9months,height was90cm and weight14kg,who’sT12is hemivertebra.Informed his familiesand won the approval.2Get the original images:The child lying down.Siemens64-slice CTtransverse scanning in supine position was done from the cervical spine tothe sacrum.All the osteal structure and discs were scaned. The thicknesswas defined as1.25mm and there is no clearance between twoscans.Obtained470CT images(the form is dicom).3Building the primary model:Imported these images into Mimics.Forgenerating the three-dimensional model,we have to mask and split theoriginal images,then calculate3D from the mask. At last,we reap theprimary model.Compare with the X-ray,the model has no significantdifference. 4Improve the model:Put the primary mode into3-Matic5.1and createthe volumes,Ligamentum flavum, Supraspinous ligament, Interspinousligament,.Then use the software Geomagic Studio12.0to building theanterior longitudinal ligament, posterior longitudinal ligament, annulusfibrosus and nucleus pulposus.The CLD, pedicle screws and orthopedicrods were made by software Creo2.0.5Simulating correction surgery:By means of software3-Matic5.1,wehad simulated the correction posterior surgery.After resected someligaments,we placed these pedicle screws,and then removed the T12hemivertebrae,installed the orthopedic rods,and closed vertebral gapbetween the T11and L1. There’s two groups,one had fixed CLD.6Finite element analysis:Imported the model into Ansys13.0,andcreated elements.Set the set the parameters such as Poisson ratio,elasticmodulus and density. When fixed support the model(constrained thebottom of the model,set the model has not displacement in X,Y,Zdirections),loaded the weight(loaded70N downward force on the top T9surface),we had applying the level force(40N、80N、120N、160N、200N)onthe top T9surface toward front,back, left and right.The resultant forcewould lead the model to simulated the bending,expending and lateralbending.To simulated the revolution we fixed the bottom,loaded theweight,and set a couple,equivalent forces(20N、40N、60N、80N、100N,120N) with opposite directions on the vertebral front edge andspinous process.Displacement diagrams of the CLD group and the NCLDgroup would be got after calculated.7Surveying the ROM：Imported all the displacement diagrams intoPhotoshop CS4,which could survey the ROM. Using SPSS13.0analysisthe result.Results：1A child’s three-dimensional finite element models of infantcongenital scoliosis which caused by hemivertebrae was builtsuccessfully(including thoraco lumbar spine,intervertebral discs and nucleus pulposus,ligaments)and the finite element models of the CLD,pedicle screws and orthopedic rods were built too.The model of spine hasno difference with the X-rays. The model has453748units and777942nodes, long49.103mm,wide60.791mm,high112.35mm,the volume is70382mm3and the total weight is0.45102kg.the Cobb angle is40.2°.2The established finite element model of pediatric scoliosis vividdescribes the features of pediatric spine:the infant vertebra is more flat andovoid slightly, in central has a little higher.The nutrient foramen is morewidely distributed than adults,beside larger aperture.:The infant vertebrahas low density,more cartilage,and the region of cancellous bone andcompact bone is difficult to distinguish.3Had complete to simulated the surgery of ligament resection,pediclescrews fixation and hemivertebrae resection.Fixed4segments,from T10toL2, established the8pedicle screws and orthopedic rods.According todifferent experimental purposes, the model can be divided into two groups,one group not to install the transverse connection device, postoperativeorthopaedic achieves satisfactory results.4Applying the ANSYS13.0analysis,we got the displacementnephogram of two groups.Measured the ROM by photoshop CS4.According to the result, We could see the displacement gradually increasesfollow the force(40N→80N→120N→160N→200N→240N). The ROMdisplayed a line growth.5The statistical analysis of two groups shows there has no statisticalsignificance in bending,expending,lateral bending and rotation.There wereno distinctly difference between the CLD group and NCLD in the2yearsold child which has congenital scoliosis caused by hemivertebrae(T12),especially when fixed4segments.Conclusions:1Using the software Mimics14.0,3-Matic5.1.etc,we built the child’sthree-dimensional finite element models of infant congenital scoliosis which caused by hemivertebrae.Succeed to simulated the correctionposterior surgery,and we obtained the spine model with CLD or not.2The established3D finite element model could set every force,makethe mechanical and displacement analysis or biomechanics study,providethe basis for biomechanics analysis and clinical study of CongenitalScoliosis(CS) caused by hemivertebrae.3There were no specific difference between the CLD group andNCLD in the2years old child which has congenital scoliosis caused byhemivertebrae (T12),provide the basis for optimize the clinical treatment.