Establishment Of A Simulation Model And A Finite Element Model And Related Biomechanical Effects Analysis Of AIS Of PUMC ⅡD_Ⅱ With Different Fusion Level

Objective:1.To establish a 3-Dimension simulation model of adolescent idiopathic scoliosis(AIS) of PUMCⅡd_Ⅱbased on the CT data with computer software MIMICS.2.To establish the 3-Dimension finite element model of AIS of PUMCⅡd_Ⅱwith the computer software ABAQUS based on the simulation model established by MIMICS.3.To research the best surgical fusion level for the AIS of PUMCⅡd_Ⅱby loading distraction force on the hypothetic pedicle site of concave side,and simulate scoliosis correction posterior approach with the FE model.4.To compare different effects of compressing on the convex side (COTCS),distracting on the concave side(DOTCS),COTCS and DOTCS at the same time,COTCS after DOTCS,COTCS before DOTCS by analysing the displacement of the upper end vertebrae(T6) based on the short 6-segmental EF modelMethods:(1) Obtain T1-S motion segment CT digital data of a AIS patient of PUMCⅡd_Ⅱ.Import the CT digital information into the computer software MIMICS,and rebuild a 3-Dimension(3D) structure by the following steps:orientation,division,erase,draw, erode,dilate,boolen operation,define polyline,calculation 3D image,remesh.We got a 3D simulation model with surface mesh finally.The model was divided into different parts,consisting of respective vertebrae,ribs and intervertebral discs,which was in total 12 thoracic vertebraes,5 lumbar vertebraes,23 ribs,17 intervertebral discs.(2)Import these parts into the computer software ABAQUS,respectively.Remesh all these parts from surface mesh into body mesh.Assemble all these parts into the same instance.Define the surface on different vertebrae,ribs and intervertebral discs. Define articular interactions as the tie between surfaces of the vertebrae and intervertebral discs.Define the interactions between surfaces of the superior articular process and inferior articular process,between surfaces of rib and vertebrae which contains two interactions--costovertebral joint and costotransverse joint.Simulate the ligament structures which contains anterior longitudinal ligament,posterior longitudinal ligament,flaval ligaments,supraspinal ligament and interspinal ligaments with spring element.Finally,the finite element model contained 224 surfaces,162 springs,78 interactions,and 34 constraints(ties),and the finite element model(EFM) of AIS PUMCⅡd_Ⅱwas consisted of 648034 nodes and 3074881 C3D4 elements.(3)Define the segment T5-S(the corresponding ribs included)as the researching object. Define the sacrum is fixed and keep no displacement on any coordinate axis(X,Y,Z). Define rib's free end(11 and 12 ribs excluded)±20mm moving range on the X,Y,Z coordinate axis.There are two curves in the EFM.One is upper thoracic curve,and the other one is the lower lumbar curve.In the upper thoracic curve,the upper end vertebrae is T5,and the lower end vertebrae is T11.In the lower lumbar curve,the upper end vertebrae is T11,and the lower end vertebrae is L4.We estimated the scoliosis correction ratio with the upper end vertebra displacement distance on the Z coordinate axis,because we presume the T5 displacement distance on the Z coordinate axis as the representative of the two curves(lower and upper curve) correction ratio,and T11 displacement distance on the Z coordinate axis as the representative of the lower lumbar curve correction ratio.We presume the result of T5 displacement minus T 11 displacement(T5-T11) as the representative of the upper thoracic curve correction ratio.As for the correction method,we use the loading distraction force on the end vertebra pedicle for simulating the adding distraction force on the pedicle screws.The loading distraction pressures were 5N,10N,20N, 50N,100N and 200N,respectively.(4) Define the segment T6-T11 without ribs as the research object.Define T8 fixed and kept no displacement on any direction.Simulate the DOTCS by loading 50N,100N and 200N distraction forces on the concave side pedicles of the end vertebrae T6 and T11 for simulating the correction of scoliosis deformity with pedicle screw.Simulate the COTCS by loading the same compressed force on the convex side pedicles of end vertebrae T6 and T11.Simulate the COTCS and the DOTCS at the same time by loading the same compressed force on the convex side pedicles and loading the same distraction force on the concave side pedicles of end vertebrae T6 and T11 at the same time.Simulate the COTCS after the DOTCS by loading the same compressed force on the convex side pedicles after offering the same distraction force on the concave side pedicles of end vertebrae T6 and T11.Simulate the COTCS before the DOTCS by loading the same compressed force on the convex side pedicles before offering the same distraction force on the concave side pedicles of end vertebrae T6 and T11.The loading force's direction was kept the same with coordinate Z axis.Measure the displacement of the T6 on the coordinate Y and Z axis. Compare the effects of all these five correction methods by measuring the displacement of T6 on the coordinate Y and Z.Evaluate which method would get the best effects on correcting the scoliosis and kyphosis deformity.Result:(1) Established a three dimensional simulation model and a finite element model of thoracolumbar motion segment successfully.(2) As for a simple short segment curve(T6-T11),DOTCS＞COTCS and DOTCS= COTCS after DOTCS=COTCS before DOTCS＞COTCS about the T6 displacement on the coordinate Z axis.(3) As for a simple short segment curve(T6-T11),COTCS＞COTCS and the DOTCS=COTCS after DOTCS=COTCS before DOTCS＞DOTCS about the T6 displacement on the coordinate Y axis.(4) As for the segment T5-S(contain the corresponding ribs) ofAIS PUMCⅡd_Ⅱ,two curve fusion＞lower lumbar curve fusion＞upper thoracic curve fusion about the displacement of T5 on the coordinate Z axis.(5) As for the segment T5-S(contain the corresponding ribs) of AIS PUMCⅡd_Ⅱ,two curve fusion＞lower lumbar curve fusion＞upper thoracic curve fusion about the displacement of T11 on the coordinate Z axis. (6) As for the segment T5-S(contain the corresponding ribs) of AIS PUMCⅡd_Ⅱ,two curve fusion＞upper thoracic curve fusion＞lower lumbar curve fusion about the displacement of T5-T11 on the coordinate Z axis.Conclusion(1)Established a three dimensional simulation model and a finite element model of thoracolumbar motion segment by using computer software(MIMICS and ABAQUS).It is possible to analyze and research the biomechanical behavior of thoracolumbar motion segment in AIS.(2)Confirm that DOTCS is better than COTCS,COTCS and DOTCS,COTCS after DOTCS,and COTCS before DOTCS on the coronal correction effect for simple thoracic scoliosis.COTCS is better than DOTCS,COTCS and DOTCS,COTCS after DOTCS,COTCS before DOTCS about the sagittal kyphosis correction effect.(3)Fusing two curves would get the best effect to the AIS of PUMCⅡd_Ⅱ.The effect of fusing two curves is better than fusing lower lumbar curve only and fusing the upper thoracic curve only.The effect of fusing lower lumbar curve is better than fusing the upper thoracic curve.