| Objective: The lumbar vertebrae are complicated and play an important role in the columnar vertebral. At present, among the biomechanical techniques, physical experiment, animal experiment, and experiments in cadavers can not reach expected effect. Three-dimension finite element analysis as a new sort of subject, is excellent to other experiments. It can repeat and change any quality or ration in the durative research. At the same time, it also offers internal and local response mechanism. Consequently, the method is being applied more and more abroad. This study was designed to establish three-dimensional reconstruction and the finite element model of the lumbar vertebrae and lumbar vertebrae osteoporosis from the CT data and to study finite element stress of the lumbar vertebrae and lumbar vertebrae osteoporosis in quasi-static load. We research the anatomical structures and features of the lumbar vertebrae and analyze the biomechanical characteristics of normal lumbar vertebrae and osteoporotic lumbar vertebrae, In order to explain the mechanism of lumbar vertebrae injury by the theory of the finite element analysis, We are hoping that this method may provide some help in the clinical diagnosis, treatment and post-evaluation.Materials and methods:1 A healthy male volunteer (25 years older, 175cm, 70kg) was selected to establish the model. After being scanned by spiral CT (120kv, 36mA, slice thickness 0.699mm, rate 0.707mm/s), 239 two-dimensional CT images were obtained. The scanning range included all lumbar vertebrae structure and discs. The CT scan data was stored into the read-write CD-ROM in DICOM files.2 The DICOM files were imported in MIMICS10.0. The 3-D lumbar vertebrae structure and discs and main ligaments models were generated from skinning the original image after thresholding, region growing and smoothing three phases. The models into reverse engineering software Geomagic studio9, except for smooth and noise processing, the resulting solid model through the assembly, access to the finite element analysis of the lumbar vertebrae structure and discs models, and through the anatomical data validation.3 Files of IGES style were imported to Ansys 9.0. The lumbar vertebrae and discs were meshed using 10-node"brick"element named SOLID 92, defined as the vertebrae and discs of the same-sexlinear-elastic material, cortical bone of lumbar's vertebrae elastic modulus 12000Mpa Poisson's ratio 0.3 spongy bone of lumbar vertebrae's elastic modulus 100Mpa,Poisson's ratio 0.2, discs's elastic modulus 40Mpa,Poisson's ratio 0.4. FE model consisted of 118095 elements and 75451 nodes. At last, 3-D finite element model of lumbar vertebrae were established.lumbar vertebrae's elastic modulus average reduce by 30%,3-D finite element model of lumbar vertebrae osteoporosis were established. .the areas of undersurface of lumbar vertebrae were fully constrained and imited to the boundary constraints, then 1000N vertical downward pressure was loaded in the primary lumbar vertebrae's superior surface,All of the loads having defined and solved, the images of equivalent stress distribution of the lumbar vertebrae model were obtained, Following by the same loads, the same force which vertical downward were loaded in lumbar vertebrae osteoporosis model, the images of equivalent stress distribution of the lumbar vertebrae osteoporosis model was obtained. The literature reported basically consistent with the finite element model data to prove that the finite element model can be used effectively.Results:Through the topics,The finite element models of the lumbar vertebrae were built, including all the bones and intervertebral discs,. There are total 70439 elements and 104071 nodes in the model, including 5 bones models, which consisted of 100266 nodes, 68110 elements and 4 intervertebral discs models consisted of 3805 node, 2329 elements; The images of Von Mises stress distribution of the lumbar vertebrae in normal lumbar vertebrae model and lumbar vertebrae osteoporosis model were obtained. The study of normal lumbar vertebrae model and lumbar vertebrae osteoporosis model finite element analysis shows: In the case of 1000N pressure condition, the stress in normal lumbar vertebrae model was gathered on fourth intervertebral discs and fifth lumbar vertebrae, in lumbar vertebrae osteoporosis model the stress also mainly concentrated during fourth intervertebral discs and fifth lumbar vertebrae. But in the same pressure condition, the stress in lumbar vertebrae osteoporosis model is smaller than the stress in normal lumbar vertebrae model, so lumbar vertebrae osteoporosis model is easier to fracture than normal lumbar vertebrae model。Conclusion:Through this experiment, we get the following conclusions:1 The CT tomography imaging through Mimics10.01 software to reconstruct a three-dimensional geometric model of the human lumbar vertebrae,intervertebral discs,main ligaments.2 Through the middle of reverse engineering software Geomagic studio9 treatment, the 3-D finite element models including vertebral body,vertebral arch,intervertebral discs of the lumbar vertebrae were established.3 In the same pressure condition,The finite element analysis of the normal lumbar vertebrae model and lumbar vertebrae osteoporosis model were carried out, The images of equivalent stress distribution were obtained. As we can see from the table, we can draw a conclusion that however normal lumbar vertebrae model or lumbar vertebrae osteoporosis model, the stress of fourth intervertebral discs and fifth lumbar vertebrae were largest. The other conclusion was that the stress in lumbar vertebrae osteoporosis model is smaller than the stress in normal lumbar vertebrae model. According to clinical cases of lumbar vertebrae injury, the fractures were most likely found at the base of the fourth intervertebral discs and fifth lumbar vertebrae, which indirectly reflected the accuracy of the finite element analysis in this experiment. And it may provide some theoretical basis for the study the etiology of lumbar vertebrae injuries.
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