Three-dimensional Finite Element Analysis In Normal And Degenerative Lower Lumbar Spine Under Different Physiological Loading

ABSTRACTObjective: The lower lumbar spine is the major structure of the human body under gravity. Low back degeneration is the most common reason that causes low back gain in the adult. The purpose of this study was to conduct three-dimensional reconstruction of the main structure of the normal and degenerative lower lumbar spine by the data of CT and MRI image, and then to finite element analysis under different physiological loading. Through this method to understand normal and degenerative lumbar spine bio-mechanics features under different physiological loading, in order to explain the mechanism of lumbar vertebrae injury by the theory of the finite element analysis. We are hoping that the method help clinicians to further understand the occurrence and development of the disease, and provide help to individualized treatment of the disease.Methods:1 A healthy male volunteer(25 years older, 174 cm, 68 kg) was selected to establish the model. After being scanned by spiral CT and MRI scanning, the scanning range include L4-L5 lumbar vertebra and intervertebral disc. Finally got the lower lumbar spine CT tomography image 236 layers, MRI fault image 98 layer; The CT and MRI scan data was stored into the read/write CD in DICOM format2 The lumbar CT tomography image combined with human anatomy data for DICOM file format to import MIMICS13.01 software, Using MIMICS software modeling form the lower lumbar spine ’s three-dimensional finite element model. Through reverse engineering software Geomagic studio12.0 optimized the model to a three-dimensional finite element entity model.3 Take the three-dimensional finite element entity model into finite element analysis software Ansys10.0. The L4,L5 vertebral body and L4/5 intervertebral disc were meshed using 10-node three-dimensional entity element SOLID,defined the elastic modulus of the cortical bone and spongy bone are 12000 Mpa,100Mpa, the Poisson’s ratio are 0.3,0.2;he elastic modulus of nucleus pulposus and fibrous ring are 1.0,450, the Poisson’s ratio are 0.49,0.3. At last, 3-D finite element model of lumbar vertebrae were established. By changing the elastic modulus and poisson ratio of L4/5 intervertebral disc, degenerative lumbar spine finite element three- dimensional model is established. fixed L5 vertebral body surface of the normal and degenerative lumbar model,taking 500 N pressure on the surface L4 of vertebral body to simulate axial compression, applying 10 N torque to simulate the mechanical changes of lumbar spine and intervertebral disc under different conditions, such as anteflexion,extension,lateral bending and rotation.Results:Based on CT and MRI scan data, through MIMICS13.01 and reverse engineering software Geomagic studio12.0 we established the three- dimensional model of lumbar spine and intervertebral disc(nucleus pulposus, fiber loop).Import the above model into ANASY10.0, divide the bone cortex and cancellous bone,coupling contact relationship between lumbar spine and intervertebral disc,fibrous ring and nucleus pulposus. Set up corresponding structure properties, elastic modulus and poisson ratio, carries on the overall and local grid division, finally we get the three-dimensional finite element model of the normal lower lumbar spine.Among it,there are 2 pieces of spine model,unit 20486,node 22934,1 piece of intervertebral disc model, unit 12110, node 13150.Using the pre-process function of ANASY10.0, By changing the elastic modulus and poisson ratio date of the nucleus pulposus and fibrous ring, to redefine the physical characteristics of different intervertebral disc organizations, and finally get the three- dimensional finite element model of intervertebral disc degeneration.Under different conditions,using the finite element analysis software Ansys10.0, through normal and degenerative lower spine model of three-dimension finite element mechanics analysis, obtained the normal and degenerative lower lumbar spine’s deformation、displacement and mechanical characteristics:For normal and degenerative lumbar vertebral body,when in the vertical compression,stress is mainly focused on vertebral bone cortex and vertebral isthmus; when in the flexed movement, stress is mainly focused on vertebral body bone frontal cortex and vertebral isthmus of anterior lateral;in posterior extension,stress is on Lumbar posterior marginal bone cortex and posterior lateral on both sides of vertebral isthmus;in lateral bending,stress is on the compressed side of Vertebral body bone cortex, vertebral vertebral isthmus and vertebral canal around;when axial rotation,Stress in vertebral vertebral isthmus stress is larger, pedicle is second; the stress situation of the degenerated lumbar vertebral body is increased than the normal.To the normal and the degenerated lumbar spine model’s displacement and deformation, the flexion is greater than extension, lateral bending is greater than the vertical compression, the rotation is slightly less than anteflexion and extension.For normal and degenerative intervertebral disc,when in the vertical compression,the fibrous ring and nucleus pulposus are under stress,the stress of fibrous ring is mainly focused on the back and transferred to the posterior lateral, the largest stress near the pedicle, which is diminishing from the back of the forward. Under different conditions, the stress of intervertebral disc focus on different areas. when in the flexed movement,stress is mainly focused on the front of the intervertebral disc; when in the extension, stress is on the back, when in the lateral bending, stress is mainly concentrated in the compression zone, The relative lateral stress decreases; when in the rotational movement,stress is on the posterior lateral and the stress on fibrous ring increased obviously; the stress on degenerative lumbar intervertebral disc is similar to the normal, but the stress on Nucleus pulposus decreased obviously, the stress of fibrous ring increased; To flexed movement, the displacement range of the normal and the degenerated intervertebral disc is greater than the extension; compared to the vertical compression, the displacement range of lateral bending movement moved to the compression side.Conclusion:Through this experiment, we get the following conclusions:Based on CT and MRI scan data, the three- dimensional finite element model of the Lumbar spine and intervertebral disc(fibrous ring,nucleus pulposus) is established and the validity of the model is validated through MIMICS13.01 and reverse engineering software Geomagic studio12.0, ANASY10.0. By changing the the nucleus pulposus and fibrous ring of elastic modulus and poisson ratio values, to redefine the characteristics of physical of The different intervertebral disc organizations, finally get the three-dimensional finite element model of intervertebral disc.Based on the normal and degenerative lower lumbar spine’s biomecha- nics analysis of the finite element, we obtained the the normal and degenerative lower lumbar spine’s biomechanics of quantitative and qualitative change, To explain the lower lumbar spine injury mechanisms provided theoretical basis of finite element simulation of biomechanics. This will help clinicians better understanding the occurrence and development of this disease, and hope to provide help for individualized treatment of the disease.