Design and finite element analysis of a new posterior atlantoaxial fixation system

English Keywords:Atlantoaxial instability  Internal fixation  Finite element analysis  Biomechanics

English Abstract:

  【Abstract】 Objectives: A new posterior atlantoaxial fixation system was designed based on imaging parameters, and its biomechanical stability was evaluated by finite element analysis. Methods: Anatomy parameters for atlas CT were measured by image archiving and communication systems measuring tool, then a new posterior atlantoaxial fixation system conformed to atlas anatomical structure was designed based on the parameters. CT thin layer scan for upper cervical spine of healthy volunteers was performed, and digital image was processed for CT diagram, then mesh division was carried out and material property, loading and boundary conditions were set to establish the normal upper cervical spine finite element model(normal model), and the effectiveness was verified by comparing with the published literature. The atlantoaxial instability finite element model(instability model) was established based on normal model by modifying the material property and removing transverse ligament. Then new posterior atlantoaxial fixation system was loaded onto the instability model to establish the new posterior atlantoaxial fixation system fixed finite element model(new model). 1.5N·m torque was applied on the new model by Abaqus 2019, and the range of motion(ROM) for flexion and extension, lateral bending and axial rotation of C0-C3 segment was calculated, then comparison with atlantoaxial pedicle screw fixed finite element model(pedicle screw model) was performed. Results: The new posterior atlantoaxial fixation system conformed to the atlas anatomical structure, and the system was formed by new type of posterior atlas arch plate, connecting rod and axial pedicle screw. Compared with the published literature, the normal model we established was effective. Compared with the normal model, the new model decreased ROM by 95.3% in flexion and extension, 92.6% in lateral bending and 99.0% in axial rotation. The ROM of implanting segment (C1-2) decreased obviously under each status. Through finite element analysis, under flexion and extension, lateral bending and axial rotation, the ROM of C1-2 segment for new model were 1.10°, 0.49° and 0.59°, which were closed to the ROM of pedicle screw model. Under flexion, extension, left bending, right bending, left rotation and right rotation, the maximum stress of C2/3 intervertebral disc for new model were 3.71MPa, 5.84MPa, 3.09MPa, 3.43MPa, 2.65MPa and 3.59MPa, which were in accordance with the normal model. The stress of new posterior atlantoaxial fixation system mainly concentrated on the root of the axial pedicle screw and the connecting rod. Conclusions: The new posterior atlantoaxial fixation system owned good biomechanical stability and can be used as a supplement for atlantoaxial instability internal fixation.