| Background:With the development of our society and changes of our lifestyle, the incidence of cervical spondylosis increased year by year, moreover, the incidence showed younger trend. Cervical traction is the most widely used and the most efficient mothod of Non-surgical treatments for cervical spondylosis. However, since the concrete operations of cervical traction in clinic lack of uniform and meticulous standards, and even we paid less attention to the security of cervical traction, the curative effect of traction may be dissatisfaction or even make symptoms aggravated. The angles of traction were of utmost importance to cervical spondylosis, traction with improper angles not only could not achieve the curative aim,but also aggravated symptoms. So, in order to understand the biomechanical principle of cervical traction better, and offer suitable angles ,it is great necessary to study the biomechanical of cervical traction.With the development of computer technology, finite element method is used widely in biomechanical research of human cervical spinal at present. Compared to the traditional biomechanical research methods, finite element method has great advantages:First, it can provide numerous models according to the researchers'demand and can be well repeated; Second, it can simulate various biomechanical states by modifying Material Properties or loading modes, such as moment , injury and surgery. From the view of clinical application, finite element method is an important and a great valuable supplementary for human cadaveric biomechanical experimental research. At present, the biomechanics of cervical traction have been studied by scholars at home and abroad, but the models of cervical always are normal structures, and there are no literatures about biomechanical investigations of cervical spine with disc degenerated.Objectives:1. To develop 3-D finite element models of normal and degenerated cervical spine (C4～C7) with detailed anatomical structure, which can be used to biomechanical investigation of cervical spine.2.To explore the effects of disc degeneration on the biomechanical behavior of the lower cervical motion segment, and which may results in a series of secondary pathological changes.3.To explore the effects of truction with different angles on the biomechanical behavior of the degenerated cervical spine, and offer suitable angles according to different nidus positions.Materials and Methods:1. Sectional images of lower cervical spine (C4～C7) were obtained from CT scans of a healthy adult male. The FEM of lower cervical spine(C4～C7) was developed with the cervical spine CT images by the combination of sofeware Mimics 10.01,Freeform and Ansys 10.0. This model was validated by comparing the average stiffness tested in flexion and extension, left lateral bending ,and left axial rotation under physiological loading with the corresponding in vitro experimental data and finite element analysis data published by other scholars. The FEM of degenerated cervical spine (C4～C7) was developed by modifying the material properties and height of the disc according to normal finite element model.2. The biomechanical parameters of two models such as the displacement of disc ,Von Mises stresses in the annulus fibrosus and intradiscal-pressure in the nucleus pulposus were measured under 45N axial compressive loading.3. The biomechanical parameters of the FEM of degenerated cervical spine such as the displacement of disc, changes of vertical distances among cervical transverses, Von Mises stresses in luschka joints, annulus fibrosus, intradiscal-pressure in the nucleus pulposus were measured under 60N traction loading with different angles ( flexion 15°, neutral and extension 15°).Results:1. A 3D finite element model of normal cervical spine (C4～C7) has been constructed and validated successfully. The average stiffness tested in flexion and extension, left lateral bending, and left axial rotation correlated well with the results by other scholars. The FEM of cervical spine (C4～C7) can be used to biomechanical investigation of cervical spine. 2. According to established finite element models, both axial compressional displacement of disc and bulge displacement of posterolateral fibrous in DDM were less than in NDM;Compared with NDM, the Von Mises stresses on both outer annular fibrosus and the top of vertebra (especially the luschka joint) were increasing but the pressure on nucleus pulposus was decreasing under 45N axial pressure in DDM.3. Under the traction of different angles, it appeared axial tensile displacement of disc and backoff displacement of dorsolateral fibrous in DDM. The axial tensile displacement of disc appeared more obvious under traction of neutral than traction of flexion 15°but the backoff displacement of dorsolateral fibrous appeared more obvious under traction of flexion 15°than traction of neutral. The distance between cervical transverse become wide when traction was applied with neutral and flexion 15°, especially traction of flexion 15°, but not obvious or even become narrow when traction was applied with extension 15°under the traction of different angles, the intradiscal-pressure in the nucleus pulposus was decreasing, especially when traction was applied with neutral. The compressive stress on fibrous and top of vertebral could be turned into tensile stress when traction was applied with neutral and flexion 15°, while when traction was applied with extension 15°,the stress on posterior and bilateral of vertebral was remain compressive stress, the anterior of vertebral turned tensile stress.Conclutions:1. The accurately anatomical 3-D finite element models of normal and degenerated cervical spine (C4～C7) were constructed successfully, which have high biofidelity and can be used to biomechanical investigation of cervical spine.2. With gradually disc degeneration , the disc and intervertenral space become narrow, the Intradiscal pressure in the nucleus pulposus decreases, while the pressures on anulus fibrosus and vertebral body (especially luschka joint) increase, which can result in rupture of fibrous annulus of cervical spine and osteoproliferation of luschka joint; The distance of cervical transverse become narrow, which can cause vertebral artery become distortion, and then result in a series of secondary pathological changes on cervical spine.3. For the early period of cervical spondylosis, which caused by herniated disc and mild osteophyte stimulating nerve root and vertebral artery, and caused by the distance between cervical transverse becoming narrow and then make vertebral artery turn distortion, we can try to use traction with flexion of small angles and neutral, while the curative effect of traction with extension may be dissatisfaction or even make symptoms aggravated.
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