Finite Element Analysis Of Different Bone Grafting Methods In The Treatment Of Thoracolumbar Burst Fractures

Objective: To compare the biomechanical analysis of transpedicular bone graft and Kambin triangle bone graft in the treatment of thoracolumbar burst fractures by finite element analysis.Methods:(1)Subject: a healthy adult male volunteer was recruited to exclude thoracolumbar diseases.The subjects were scanned with American GE 64 slice spiral CT,and 358 T12-L2 thin-slice images were obtained.(2)Establish a normal T12-L2 geometric model: export the acquired image data in DICOM format,and import it into Mimics16.0 to obtain STL format model of T12-L2 vertebral body.The STL models of T12-L2 vertebrae reconstructed by CT were imported into Geomagic studio2014.The STL models of all vertebrae were transformed into the three-dimensional solid geometric models of T12-L2 thoracolumbar vertebrae and served as normal geometric model group.The normal geometric model group was imported into Proe5.0,and 60% of cortical bone and cancellous bone in the anterior and middle column of L1 were removed by geometric editing function to simulate thoracolumbar burst fracture.On this basis,the universal spinal internal fixation system(USS,screw rod straight 6 mm)was used for T12 and L2,and two different bone grafting methods were simulated for L1 injured vertebrae: transpedicular bone grafting and Kambin triangle bone grafting.Group 1: posterior internal fixation + transpedicular interbody fusion(the bone graft area is located near the screw rod,showing a figure of eight);Group 2: posterior internal fixation + interbody fusion through the Kambin triangle(the bone graft location is different from the bone graft method 1,the bone graft area is located in the middle of the L1 injured vertebral cancellous bone area,and the amount of bone graft is the same as the method 1);Group 3: posterior internal fixation + interbody fusion through the Kambin triangle(the bone graft location is different from the bone graft method 1,the position of bone graft is different from that of mode one,and is similar to that of mode two.The bone graft area is located in the middle of the cancellous bone area of L1 injured vertebrae,and the amount of bone graft is much larger than that of mode two).The four groups of geometric models are exported as step files.(3)T12-L2 finite element mesh generation,material parameter definition,boundary condition setting: four groups of T12-L2 thoracolumbar structural geometric model STP files were imported into hypermesh14.0 for mesh generation.Then the T12-L2 finite element mesh model file is imported MSC.Patran2012,the properties of finite element mesh,the definition of material parameters,the application of load and the constraint of boundary conditions are set.At the end of the day MSC.Nastran2012 is used to set various working conditions,calculate and analyze,and extract calculation results.Results: The three-dimensional finite element simulation of different bone grafting methods was carried out by using finite element method,and the von Mises equations of corresponding intervertebral disc,vertebral body,endplate,intervertebral joint,screw rod and other structures of thoracolumbar spine were analyzed qualitatively and quantitatively The results are as follows:(1)the stress of the upper and lower endplates of L1 vertebral body: the stress of the upper and lower endplates of L1 vertebral body in the four groups of thoracolumbar models is the largest,about1.66 MPa and 1.49 MPa,in the flexion state,and the stress of the upper and lower endplates of L1 vertebral body in the extension state is the smallest.From different motion states,comprehensive analysis showed that the stress of L1 upper and lower endplates in the bone graft group 3 was lower than that in the bone graft group 1,which indicated that the stress of L1 upper and lower endplates in the bone graft group 1 was lower than that in the bone graft group 3 when the amount of bone graft was the same and the location of bone graft was different.,(2)Stress of adjacent intervertebral discs of L1: the stress values of T12-L1 intervertebral discs and L1-L2 intervertebral discs of several groups were the highest in the normal group under the left and right bending state.For the three bone graft groups,the stress of the adjacent discs in the first group was relatively large in the flexion state,and the stress of the T12-L1 discs of the bone graft group 3in the upright state was the smallest.According to different motion states,in flexion,left rotation and right rotation states,the stress of the bone graft group 1 of L1-L2 intervertebral discs in bone graft group was the largest,and the stress increment was also the largest compared with the normal group.In the bone graft group,the stress of adjacent intervertebral discs decreased gradually in neutral,flexion,left rotation and right rotation,and the stress of adjacent intervertebral discs decreased more than in the bone graft group.The stress values of adjacent intervertebral discs in the bone graft group 2 were basically between the bone graft group 1 and group 2.(3)Stress of vertebral body: due to the setting of screw rod structure,the main stress concentration of cortical bone of T12 and L2 vertebral bodies in the three bone graft groups occurred near the screw hole,which was much larger than that in the normal group.Compared with the stress of cortical bone and cancellous bone of L1 vertebral body in normal group,the stress of three bone graft groups decreased more in each movement state.(4)The stress of screw and rod: in different movement states,the stress value of screw and rod corresponding to three different bone grafting methods had no significant difference,and the difference was less than 3.6%.(5)The stress of upper and lower joints on both sides of L1: the peak stress of upper and lower joints in normal group was about 0.19mpa-8.82 mpa.The peak stress of the upper and lower joints of L1 in the three bone graft groups was about 0.24MPa-4.64 MPa,which was significantly lower than that in the normal group.Three different bone grafting methods had little effect on the stress of the upper and lower joints of the injured vertebrae after posterior screw rod fixation,and the difference was less than 8.8%.Conclusion: Compared with transpedicular bone grafting,Kambin triangle bone grafting can further reduce the peak stress of adjacent intervertebral discs,upper and lower endplates,cortical bone and cancellous bone of the injured vertebrae.Even when the amount of bone grafting is the same,but the distribution of bone grafting is different,the adjacent structure of the injured vertebra corresponding to the bone graft in the Kambin triangle is less stressed than transpedicular bone grafting.