| Objective: Cervical myelopathy is one of the formal diseases in spinal surgery. Its pathogeny is correlated with spinal biomechanics. At present, among the biomechanical techniques, animal experiment, physical 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 local and internal response mechanism. Consequently, the method is being applied more and more abroad. Cervical vertebra is a functional macrocosm. Each part of it is different and stress transmission is very complex. It can not reflect the whole instance to adopt functional spinal unit. So this study applied finite element analysis establish lower cervical three-dimension model and research the spinal stress changes in flexion and extension in order to clarify the pathogeny of cervical myelopathy in biomechanics. Then support reference in the prevention of clinical diseases. Furthermore, this established model can also be used to design inner fixers and analyse operative style. And settle the basic for spreading finite element analysis to therapy of clinical diseases. Methods: Selecting a healthy female volunteer aged 25 years old(65kg, 170mm) to do CT scanning. Layer thickness was 1mm and space between two scans was 0mm. The scanning range included all osteal structure and discs.90 pictures were obtained and 75 were applied for modeling. Datas were saved in CD which can be read and written. Before dealing with the original pictures, to divide the vertebrae and discs in Photoshop software and saved them as JPG style. Applying C-basic program to test the divided images and pick up boundary coordinate. Then the images were saved as single cloud files. To import these files to Geomagic software and get entity models, which were saved as IGES style. Next, files of IGES style were imported to Ansys 9.0. The vertebrae and discs were meshed using 10-node"brick"element named SOLID 92. The ligaments were modeled using 2-node nonlinear link element named LINK 10, which only permit tensile axial force transmission. The FE model consisted of 110577 elements and 69616 nodes. In the analysis, the weight of the skull was simulated by applying vertial load of 45N on the C3 facet, and the inferior surface of the C7 vertebral body was fully constrained. Pure moment loading of 2.0N.m was applied to simulate the movement of the cervical spine under flexion and tension. Then the images of equivalent stress distribution were obtained.Results: From the images, we could find in general, the stress in facet joints in lower cervical spine was gathered from top to bottom and mainly concentrated during C4/5 and C5/6. In flexion, the stresses in C5/6, C6/7 were larger than others. In tension, the stresses in C4/5, C5/6 were larger. The facet joints permitted tensile force in Z axis in flexion but permitted press stress force in tension. This can be concluded that facet joints can support and conduct loading when extending.Conclusion: The stress of facet joints in flexion and tension generally concentrated in medial and inferior cervical spine, especially in C4/5 and C5/6. This conclusion expatiated that degeneration of facet joints mostly appeared in medial and inferior cervical spine from biomechanical point of view. Therefore, when the human body was always in bad pose(such as flexion), the local stress especially in facet joints would increase. The increased stress resulted in osseous hyperplasia, and serious hyperplasia could stimulate nerve roots. At last, this vicious circle made for cervical myelopathy. So that, the people who usually do office work should lower their head moderately. When they have a rest, they would better relax cervical muscles and change location regularly. Accordingly, the situation of stress concentration can be improved. In this way, people can prevent the cause of cervical myelopathy.
|
PDF Full Text Request