3-D Finite Element Analysis Of Biomechanical Changes Of Lower Cervical Spine In Flexion And Extension

Objective: Recently, the incidence of cervical myelopathy is increasing year by year. Operation becomes the only choice after the invalid keeping treatment. But the appearance of many syndromes after the traditional fusion was a difficult problem which puzzled clinical physicians. To solve the problem of appeared abnormal stresses of adjacent segment after fusion, a new point of view namely " non-fusion fixation technology" or "dynamic fixation" has appeared since 1990s. As one of the mature methods, the success of placement and its excellent curative effects made the biomechanical study of cervical artificial discs was in the ascendant.As a digital simulated analyse, this study adopt entity model, different with in vitro model. It can reflect human biological character, especially the simulation of ligament and disc prosthesis are more close to the real configuration. To analyze the movement of normal range with mechanical methods,we can find out the kinematic speciality and compare with the former literature, thereby to evaluate the lower cervical spinal movement of the patient after placement of a vertebrae material and methodsMethods: Choosing a patient after placement of an artificial disc prosthesis 6 months, male, 48 years, 170cm, 65kg, without osteal abnormity and spinal monstrosity. Using the helix scan from top to bottom. Layer thickness was 0.6mm and space between two scans was 0mm. The extension included all the component of C4-C7 such as vertebrae, ligaments, discs and one artificial disc prosthesis. 392pictures were obtained and 367 were applied for modeling. Datas were saved in CD which can be read and written. Applying C-basic program to test the divided images and pick up the boundary coordinate of C4-C7 osteal configuration and discs. Then the images were saved as single cloud files. To import these files to Geomagic software. The model went through "point phase", "polygon phase" and "shape phase", then made NURBS surface. The entity models 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. The endplates and annulus fibrosus were meshed as a system, but the nucleus was distinguished. In order to compare with the former studies, the inferior surface of C7 vertebral body was fully constrained. Pure moment loading of 2.0 N.m was applied incrementally on C4 facet along the various anatomical planes to simulate the movements of the lower cervical spine under flexion, extension, axial rotation and lateral bending configurations. This study mainly analysed the HAM of each functional spinal unit (FSU) and rotational angels.Results: The specialty of this model: According to the CT scans after operation and c-basic program to obtain the image. The geometrical shape and constructions were simulated well. Otherwise, we built the C3-C7 FE model by using the lower cervical spine which included Bryan^TM disc. This method was more accord with clinical requires. Compared with other's test, most of the results fell within one standard deviation of experimental data. The result of extension was larger than experiment. This was likely to relate to the excision of C5-C6 ALL in the operation.Conclusion: In the part of maintaining the stabilization of cervical spine, vertebrae, discs, joints, muscles and ligaments all take the important effects. Actually, most operations of cervical spine destroyed the stabilization directly or indirectly. This leads to the concentration of stresses and accelerated the degeneration. So we should reduce the breakage in the operation. Via the analyse of the DOF of the model, we could conclude the placement of a artificial disc prosthesis affect the movement of the lower cervical spine limitedly, and this operation could maintain the stabilization of lower cervical spine.