Research On Biomechanical Characteristics Of Occipitoatlantoaxial Complex In Situation Of Malformation And Operation Procedures

Research on clinical medicine indicates that relative pathological changes in occipitalatlantoaxial complex are more likely to happen based on congenital bony malformation. The most common seen changes are occipitalization of atlas and atlantoaxial dislocation, whose treatments generally need two operations: odontoidectomy, and posterior internal fixation. However, currently it is not clear about the biomechanical characteristic changes and their process caused by congenital malformation and operation. Now clinical observation is the major method of operation evaluation, lack of basic research. And whether the above changes can be known or not will directly affect the accuracy of clinical diagnosis and treatment choice.Through research on physical structure, anatomical structure, and movement characteristics of occipitalatlantoaxial complex, the simplified model proposal has been put forward. 3D reconstruction of occipital atlantoaxial complex has been completed and point cloud data has been obtained by collecting cervical spine CT pictures and using medical imaging processing software Mimics. In addition, reverse engineering approach is used to accomplish the surface reconstruction of bone structure and to establish geometric model of occipitalatlantoaxial complex with accurate anatomical structure. Meanwhile, all-hexahedral mesh finite element model including articular cartilage is built through the application of TrueGrid, and 3D finite element model is also set up based on the research of biological material attributes and Contact Mechanics. Furthermore, combined with the corpse experiment data, under the condition of 0.3Nm and 1.5Nm external applied load, the author of this paper has done nonlinear finite element contact analysis of four physical movements, such as flexion, extension, lateral bending, and axial rotation, and its effectiveness is also verified. With the verified finite element model as a basis, data about biomechanical characteristics of occipitalatlantoaxial complex under four physical movements is obtained through the establishment and comparative analysis of finite element model of occipitalization of atlas, odontoidectomy, and posterior internal fixation.The verified result of model validation indicates that except the axial rotation angle of srticulatio atlantooccipitalis is slightly 0.5°larger, all the other data well match that of the corpse experiment, and the nonlinear model movement as well as ligament strain are mainly consistent with the actual physical situation. The analysis result states that occipitalization of atlas alone is impossible to directly cause atlantoaxial dislocation or half dislocation, but it can change the biomechanical characteristics in this region, increasing the possibility of cartilage injury and decreasing the model's stability. It also indicates that odontoidectomy enlarges movement angle and reduces stability, and posterior internal fixation can restore stability at the cost of losing movement characteristics in this region.Through the research on establishing finite element model of occipitalatlantoaxial complex, this paper has discovered an effective approach to the establishment of finite element model of occipitalatlantoaxial complex. Meanwhile, by nonlinear finite element contact analysis and research on the effects to biomechanical characteristics made by occipitalization of atlas and operation, this paper more deeply understands congenital malformation in this region and the operation effectiveness. The research result is of higher practicability and clinical reference value.