| BackgroundUpper cervical spine instability is a common clinical subjects disease, can cause a range of clinical symptoms, spinal disorders is hot and difficult research. Compared with the cervical spine instability and dislocation, the difference lies in the degree of instability. Upper cervical spine instability occurs during exercise, resulting in difficulty imaging diagnosis. Chinese medicine has long been recognized that the presence of cervical spine instability, which was classified as "wrong bone joints, tendons wrong slot" category. In clinical practice, Chinese medicine treatment of cervical spine instability technique has a good effect. Due to lack of support for basic research, bio-mechanical mechanism on the cervical spine instability is not yet clear, the impact of clinical studies and efficacy evaluation of the disease.Biomechanical factors is an important factor in the study of the occurrence and development of cervical diseases that need to be considered, it is of great significance in scientific research. Establish upper cervical spine instability model to simulate different conditions by finite element software, can be compared to analysis of multiple test hypotheses. Thus, compared to the traditional pure physics experiments, animal studies, in vitro experiments, samples, using the finite element technology can not only be more truly reflect the physiological or pathological features of the cervical spine, making analysis more accurate, but also has simple, re-use and other advantages. Application of Finite Element rapid technological development in the field of bio-mechanics. Since foreign scholars established the first lumbar dimensional finite element model and simulate biomechanical analysis, research domestic aspects of spinal vertebrae gradually from the establishment of an independent model to model and from the whole spine build development of the spine and then on the finite element model of spinal diseases Research on the basis of pathogenesis, preoperative planning and postoperative evaluation and so on. But the upper cervical spine dynamic finite element model at home and abroad to establish a little, the dynamic model of instability is blank. Produce high-quality cervical instability on dynamic finite element model can better reflect on the cervical spine instability during biomechanical change characteristics, provide a reliable theoretical basis for imaging diagnosis of the disease has important scientific value.ObjectiveEstablish upper cervical spine instability of three-dimensional dynamic simulation model to analyze the state of motion of cervical spine instability, specifically the kinematic characteristics of cervical spine instability, to understand the impact of changes to the mechanics of cervical ligamentous structures on the cervical stability.MethodsUsing fresh cervical specimens for the study, after a CT scan using the finite element software cervical reconstruction on 3D models, and by way of the fatigue load so that the specimen ligament stress relaxation on the establishment of cervical spine instability model, using motion capture move normal cervical instability model and measurement model on the system state trajectory flexion position during exercise, ligaments and other parameters set by image registration, the dynamic model of the cervical spine in order to establish normal and instability after and mechanical analysis, to explore the upper cervical spine relations ligament instability and changes in structural mechanics degree,resultHigh degree of simulation of the upper cervical spine finite element model experiment established good geometric similarity. Finite element analysis showed that:Under physiological conditions, the process of the upper cervical spine flexion, yellow ligament ligament strain produces the most prominent, followed by atlantoaxial anterior longitudinal ligament; maximum rigidity cruciate ligament, followed by sudden sharp teeth ligament, per unit area the forces to atlantoaxial anterior longitudinal ligament and yellow ligament is most obvious, posterior longitudinal ligament and alar ligament force minimum; ligament stress in dens see the highest ligament, followed by atlantoaxial anterior longitudinal ligament; atlanto-occipital joint relative movement angle of 3.49°, relative motion atlantoaxial joint angle of 8.84°. After cervical extension process, ligament strain generated in atlantoaxial anterior longitudinal ligament of the most prominent, followed by tooth cusp ligament; force per unit area situation to odontoid ligament and atlantoaxial anterior longitudinal ligament is most evident, followed by wing-shaped ligament and yellow ligament, posterior longitudinal ligament almost no force; atlanto-occipital joint motion relative angle 11.16°, relative motion atlantoaxial joint angle of 14.20°. In the unstable state, the upper cervical flexion during ligament strain produces yellow ligament is most prominent, followed by atlantoaxial anterior longitudinal ligament; maximum rigidity cruciate ligament, followed by sudden sharp teeth ligament, force per unit area in the case of the atlas pivot anterior longitudinal ligament and yellow ligament is most obvious, posterior longitudinal ligament and alar ligament force minimum; ligament stress to atlantoaxial anterior longitudinal highest ligament, followed by tooth cusp ligament; atlanto-occipital joint relative movement angle of 5.51°, atlantoaxial joint relative motion angle 13.70°. After cervical extension process, ligament strain generated in atlantoaxial anterior longitudinal ligament of the most prominent, followed by the alar ligament; force per unit area case to the alar ligament and atlantoaxial anterior longitudinal ligament is most evident, followed by tooth cusp ligament, posterior longitudinal ligament almost without force; atlanto-occipital joint motion relative angle 12.96°, relative motion atlantoaxial joint angle of 17.20°, we can see, through the fatigue loading can lead to increased and atlanto-occipital joint atlantoaxial articulation angle, which in atlantoaxial joint flexion activities most obvious.ConclusionBinding assay data shows connection atlantoaxial yellow ligament of the cervical limit excessive flexion played an important role, and alar ligament and anterior longitudinal ligament of the cervical spine after over-stretching the act as a restraint, while the anterior longitudinal longitudinal ligament and cruciate ligament for the vertebral flexion there is a certain limiting effect, but the anterior longitudinal ligament is more biased in favor of extension of limits and restrictions on the power of longitudinal ligament weak. At the same time in the direction of flexion instability after atlantoaxial joint angle of movement increased significantly, while the atlanto-occipital joint inconspicuous; the extension direction and angle of movement atlantooccipital joint atlantoaxial joint changes are not obvious. Considering the analysis of a larger number of ligament limit on overall cervical vertebrae extending and stiffness, when it is in the cervical extension, deformation ligament produce much, and therefore change the angle was not obvious; on the contrary, the former the bend direction, mainly by yellow vertebral ligament constraint, but low yellow ligament stiffness, so when subjected to stress flexion direction will have a greater deformation, resulting in a significant increase in the atlantoaxial articulation angles. It can also explain, frequent or prolonged flexion activities are more likely to cause damage to the cervical spine, leading to the occurrence of cervical instability. Overall, the summary link using finite element technology and motion capture system on cervical dynamic finite element model can jointly build a better analysis of the process of cervical spine instability between stress and ligament instability degree, for the disease Biomechanical study of clinical diagnosis and provide a basis. |
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