Validation of the Neutral Zone of a C0-C1-C2 FE Complex

It has been theorized that the neutral zone (NZ) may be a more sensitive parameter of spinal instability than the range of motion (ROM). An anatomic detailed, nonlinear finite element (FE) model of the occipito-atlanto-axial (C0-C1-C2) complex based on Visible Human Male dataset was developed in this study, which can improve the previous upper cervical spine FE models by its increased geometric modeling accuracy and more precise material assignment. According to the analysis of the motions of each vertebral level under physiological static loadings to simulate the movements of upper cervical spine under axial rotation, flexion, extension, and lateral bending, the ROMs and NZs agreed well with published experimental data. The moment-rotation relationship predicted by this model was apparently nonlinear, and the largest rotation was predicted in horizontal plane, followed by median plane and coronal plane. The complex exhibited large ROMs and high proportions of NZ to ROM. According to our knowledge, there are no published results of FE models of upper cervical spine by far that have already undergone validations for both ROM and NZ under physiologic loads and are in good agreement with experimental data. The findings of the validation of this newly-developed model also coincide with the experimental studies. Therefore, it can be concluded that the current FE model validated for NZ is useful in the investigation of abnormal NZ in disease and trauma.