Finite Element Modeling And Bio-mechanical Analysis Of Posterior Atlantoaxial Fixation

Objectives:To study the stability and bio-mechanical analysis of two upper cervical fixation with three-dimensional finite element models, then to guide the clinical application of the two fixation methods, comparing their advantages and disadvantages.Summary of Background Data:Compared with the C2 pedicle screw fixation, there is few risk of vertebral artery injury using C2 laminar screw fixation, so it can be regarded as a necessary complement to the existing operation methods, however there are still some drawbacks such as the possibility of spinal cord injury with the laminar walls pierced by screws. As laminar screw fixation is applied to only a few cases and lack of appropriate laboratory bio-mechanical analysis, it is difficult to determine the superiority of the two fixations.Methods:A nonlinear three-dimensional finite element model was developed with anatomic details from computed tomographic images from the occiput to C3.Then a fixation system was added to the model with different methods to establish C2 pedicle screw fixation and interlaminar screw fixation models. The three models were operated for flexion, extension, axial rotation and lateral bending with physiological loads to simulate the normal movements and study the bio-mechanical analysis.Results:All the ranges of motion of the three models in different motion states were measured and verified with the lab results. Both fixation techniques can significantly reduce motion compared to the intact model. There were no statistically significant differences between the C2 intralaminar and pedicle screw techniques.10 different nodes were collected from the 4 laminar walls of each model, then the Von Mises stress of all the nodes were measured and compared, indicating that the stress of internal wall is generally not higher than the external wall in different motion states.Conclusions:C2 intralaminar screw fixation and pedicle screw fixation can provide similar stability for the upper cervical spine,and the former has few risk of vertebral artery injury. But there is still possibility of spinal cord injuries with screws penetration, even though the stress of internal wall is generally not higher than the external wall when the intralaminar screws fixed. Therefore C2 laminar screw technique is a useful complement to but difficult to completely replace the pedicle screw technique, which requires clinicians to assess and decide which one to adopt to achieve the best therapeutic effect...