Finite Element Analysis Of Stress Zoning Of Lumbar 1 Vertebra

Purpose:(1)The physiological stress model of normal thoracolumbar vertebrae(from T11 to L2)was constructed by finite element analysis;(2)To observe the stress distribution of cortical bone and cancellous bone of lumbar 1 vertebra(L1)in different groups(α group,β group,γ group);(3)The stress distribution law of L1 vertebral body is summarized,and combined with anatomy and imaging analysis,the conception of stress zoning is put forward and verified by statistical methods,and finally the six-zoning method is put forward;(4)To explore the clinical significance of six-zoning methodMaterials and Methods:(1)Research object: Three healthy volunteers aged from 18 to 50 years old were selected,the imaging data of thoracolumbar vertebrae(thoracolumbar DR film,thoracolumbar CT,thoracolumbar junction MRI)showed no obvious abnormality;Bone mineral density examination indicates that volunteers with normal bone mass;Patients with spine-related diseases or other diseases are excluded;(2)Data collection :Three volunteers underwent plain CT scan of thoracolumbar segment(T10-L3 sagittal,transverse and coronal).The scanning thickness was 0.625 mm.The data were stored in DICOM format on the hard disk for use;(3)Construction of three-dimensional finite element model of normal thoracolumbar vertebra(T11-L2): Import the prepared hard disk data into Mimics,identify the different tissue structure thresholds of the thoracolumbar segment,select the appropriate T11-L2 cortical bone threshold to read,and construct the T11-L2 vertebral shell model for preservation;(4)Generation of threedimensional finite element model of normal thoracolumbar vertebral body: the empty shell model of T11-L2 vertebral body was introduced into Geomagic for fairing and perfect repair,and then re-introduced into Mimics,to generate thoracolumbar accessory structure and tissue(vertebral cortical bone,cancellous bone,endplate,annulus fibrosus,nucleus pulposus,articular process);(5)Using SoliderWorks to optimize each part;(6)Import the improved model into HyperMesh for assembly and material assignment;(7)Finally,the mechanical loading was carried out by using Abaqus,and different grades of compression loads(500N,600 N,700N)were applied to 3 normal thoracolumbar vertebrae models to simulate the axial compression of the vertebral body,plus 7.5N.m bending moment,to simulate the load of the vertebral body in the state of flexion,extension,lateral flexion and rotation;(8)Grouping: the five motion states(axial compression,flexion,extension,lateral flexion and rotation)produced by vertebral body under 500 N axial compression and 7.5N.m bending moment load are called α group,the five motion states produced by vertebral body under 600 N axial compression and 7.5N bending moment load are called β group,and the five motion states produced by vertebral body under 700 N axial compression and 7.5N bending moment load are called γ group;(9)Division: the upper and lower edge of L1 vertebral body was fixed and segmented from the median cross-section.the vertebral body was divided into two uniform parts,the upper part was called area A and the lower part was called area B.Each part of the vertebral body is evenly divided into 6 segments on the distance from the central surface to the edge of the vertebral body,and the secondary stress from the outside to the inside is as follows: 1,2,3,4,5,6,and the upper and lower parts form a three-dimensional circular cylindrical 6 part,a total of 12 parts.the load data of 12 parts of L1 vertebral body were uniformly collected respectively;(10)The pairwise T test of the average load stress value in the adjacent area of L1 vertebral body was carried out by using SPSS,and finally the stress distribution of L1 vertebral body in different groups was analyzed,and the stress zoning was obtained.Result:1.In group α,group β and group γ,the stress of cortical bone and cancellous bone of L1 vertebral body was mainly concentrated in the center of the posterior edge of the upper part of the vertebral body(area A)under axial loading.during flexion loading,the stress was mainly concentrated in the center of the anterior edge of the upper part of the vertebral body(area A),and during extension loading,most of the stress was concentrated in the center of the posterior edge of the upper part of the vertebral body(area A),and a small part was concentrated in the center of the anterior edge of the upper part of the vertebral body(area A).During lateral flexion,the stress is concentrated on the external posterior edge of the ipsilateral vertebra,and during rotational loading,the stress is concentrated in the center of the posterior edge of the vertebral body and part of the ipsilateral posterior edge..2.In α,β and γ groups,the cortical and cancellous bones in region A and region B were compared,and the differences were statistically significant.3.In group α,both cortical bone and cancellous bone satisfied the comparison between A1 region and A2 region,there was no significant difference between A2 region and A3 region,there was significant difference between A3 region and A4 region,and there was no significant difference among A4 region,A5 region and A6 region.There was significant difference between B1 region and B2 region,there was no significant difference between B2 region and B3 region,there was significant difference between B3 region and B4 region,and there was no significant difference among B4 region vsB5 region,B6 region vs B4 region and B5 region vs B6 region.In β group,the A region and B region of cortical bone met the statistical law of α group,and the cancellous bone almost satisfied the statistical law of α group.Only A4 region and A5 region,B4 region and B5 region were compared with each other.The difference was statistically significant,which was slightly inconsistent with that in α group.In γ group,most of the A and B regions in cortical bone and cancellous bone met the statistical rules of α group,only A4 region and A5 region,B4 region and B5 region were compared with each other,the difference was statistically significant,which was slightly different from that in α group.Conclusion :In this experiment,a three-dimensional finite element model of normal thoracolumbar vertebrae(T11-L2)was constructed,and the stress distribution of L1 vertebrae in α group,β group and γ group was observed and analyzed.Combined with clinical imaging investigation and analysis,stress zoning was proposed.1.The construction of thoracolumbar vertebra(T11~L2)model in this experiment is real and effective,which lays a foundation for further mechanical analysis and research.2.In group α,group β and group γ,the stress distribution of L1 vertebral body from the sagittal plane is mainly concentrated in the upper half of the vertebral body(area A).From the cross section,the stress is mainly concentrated on the outer edge of the vertebral body,and the stress in the center of the vertebral body is less.it can be seen that the stress concentration trend is located in the upper edge and outer edge of the vertebral body.3.There were significant differences in stress distribution of cortical bone and cancellous bone between region A and region B in α group,β group and γ group.There are statistical differences in stress distribution in A Ⅰ,AⅡ and AⅢ areas,and in B Ⅰ,BⅡ and BⅢ regions.4.L1 vertebral body is divided into six circular regions with different volumes and sizes,namely A Ⅰ,A Ⅱ,A Ⅲ,B Ⅰ,B Ⅱ and B Ⅲ,which is called six-zone method.The stress in the AII region of L1 vertebral body is the most concentrated,which is called the core stress area.The A Ⅰ + B Ⅰ + B Ⅱ region accounts for most of the stress of L1 vertebral body,which is called the main stress area.The area of AⅢ + BⅢ is called the secondary stress zone.