Establishment And Analysis Of A Three-dimensional Finite Element Model Of Atlantoaxial Dislocation

ObjectivesTo establish and validate a three-dimensional finite element model of the upper cervical spine. Base on this model, establish a three-dimensional finite element model of atlantoaxial dislocation and evaluate its feasibility in clinical study and biomechanical research.Materials and MethodsThe upper cervical spine (C0-3) geometries were determined from CT images of a healthy volunteer. Finite element modeling softwares were used to develop a geometric model of upper cervical spine. The ligaments were added to the model based on data from the literature. The model was analyzed and calculated by finite element analysis softwares. Pure moment loading of 1.5N·m was applied to the model to simulate various movements of the cervical spine under flexion, extension, axial rotation and lateral bending configurations. To validate the C0-3 finite element model, the predicted kinematic data, in term of the range of motion (ROM) , under different static loading configurations were analyzed and compared against the experimental data by Panjabi and finite element models of upper cervical spine established by Brolin K and Zhang.Based on the finite element model of a normal upper cervical spine,a finite element model of atlantoaxial anterior displacement due to C1 transverse ligament rupture without fracture was developed according to a clinical case. The range of motion under flexion-extension, lateral bending and axial rotation were measured and analyzed in the normal and abnormal model.Two kinds of internal instrument of upper cervical spine were loaded on the abnormal model. The range of motion under flexion-extension, lateral bending and axial rotation were measured and analyzed.Results1.The normal model of upper cervical spine was built clearly and distinctly, with good geometric similarity, consists of 72500 nodes and 206747 elements, the results of the normal model were matched to the results of the in vitro experiment of biomechanics by Panjabi et al., also to results of finite element models of upper cervical spine established by Brolin K and Zhang.2.The finite element model of atlantoaxial dislocation with C1 transverse ligament rupture without odontoid fracture was similar with clinical case. The range of motion was larger in abnormal model than in the normal model, especially in flexion and extension in which the range of motion increased by 17.8°and 13.7°, respectively.3.The finite element model loaed with atlantoaxial pedicle screw fixation or bilateral C1-2 transarticular screw combined with C1 laminar hook fixation were similar with clinical case. The ROM of bilateral C1-2 transarticular screw combined with C1 laminar hook fixation was less than atlantoaxial pedicle screw fixation. Atlantoaxial pedicle screw fixation had maximum stress on the root of pedicle screw and connecting rod under extension position. Bilateral C1-2 transarticular screw combined with C1 laminar hook fixation had maximum stress on the root and transarticular part of the screw.Conclusions1.The finite element model of the upper cervical spine realistically simulates the complex kinematics of the craniocervical region which can simulate the natural condition and facilitate the further biomechanical research.2.The method to establish a finite element model of atlantoaxial dislocation is feasible.The finite element model can be used to simulate the biomechanics of atlantoaxial dislocation with transverse atlantal ligament rupture without odontoid fracture,which is helpful to determine the treating strategy.3.The finite element model of atlantoaxial dislocation can be used for biomechanical research, especially biomechanical analysis of internal fixation. Bilateral C1-2 transarticular screw combined with C1 laminar hook fixation is more stable than atlantoaxial pedicle screw fixation.