Finite element analysis of the different fracture mechanisms of the odontoid process caused by different body positions of the cervical spine

English Keywords:Odontoid fracture  Finite element  Upper cervical spine injury

English Abstract:

  【Abstract】 Objectives: To analyze the correlation between cervical spine postures and different types of odontoid fractures when injured in different directions of violence using finite element method. Methods: Based on the experience of establishing the finite element model of the upper cervical vertebrae in the early stage, and verified as effective through literature published abroad and in vitro experiments, different positions of the cervical spine(neutral position, flexion position, extension position, lateral bending position, and rotation position) were preset on the established three-dimensional nonlinear finite element model of the normal occipital-atlantoaxial complex, and an acceleration of 8m/s2 was applied in each direction of violence[anterior, posterior, lateral, top(vertical downward)]. The von Mises stress values in different regions of different types(Anderson and D′Alonzo type) of odontoid process fractures were calculated, and stress contour maps were extracted. Results: When subjected to anterior violence, the maximum von Mises stress values were generated in an extension position, with stress concentration in the vertebral body of the axis(Type Ⅲ)(0.41MPa). When subjected to posterior violence, the maximum von Mises stress values were generated when the cervical vertebrae were in a flexion position, with stress concentration in the odontoid process base(Type Ⅱ)(0.52MPa) and the vertebral body of the axis(Type Ⅲ)(0.55MPa). When subjected to lateral violence, the maximum von Mises stress values were generated when the cervical vertebrae were in a flexion position, with stress concentration in the odontoid process base(Type Ⅱ)(0.51MPa) and the vertebral body of the axis(Type Ⅲ)(0.43MPa). When subjected to vertical downward violence, the stress values in each body position increased significantly, the stress at the tip of the odontoid process(Type Ⅰ) in the flexion position reached 0.99MPa, the stress at the base of the odontoid process(Type Ⅱ) in the lateral flexion position reached 1.16MPa, and the stress at the axis vertebral body(Type Ⅲ) in the rotational position was 0.85MPa. Conclusions: When the upper cervical spine is in a flexion position and receives a vertically downward force, it is prone to odontoid process tip fractures(Type I); When the upper cervical spine is in a flexion position and receives a posterior or lateral force, or when it is in a lateral bending position and receives a vertically downward force, it is prone to odontoid process base fractures(Type Ⅱ); When the upper cervical spine is in a flexion position and receives a posterior force, or when it is in a rotational position and receives a vertically downward force, it is prone to axis vertebral body fractures(Type Ⅲ).