Biomechanical analysis of C4-C6 spine segment considering anisotropy of annulus fibrosus.

Based on computed tomography scanning images of human cervical spine, this paper develops a detailed and anatomically accurate finite element model for C4-C6 motion segment to investigate its biomechanical responses. The model includes vertebrae, intervertebral disc, and various ligaments. The annulus fibrosus is characterized by using a previously developed nonlinear, anisotropic, hyperelastic fiber-reinforced model with fiber-matrix shear interaction considered. Other materials are simplified as linear or nonlinear elastic. The proposed cervical model is first validated by comparing numerical force-displacement relationship and intradiscal pressure under axial compression with experimental data available in the literature. The biomechanical responses of the spine segment under axial compression and rotation are then investigated. It is found that the fiber matrix-shear interaction of the annulus fibrosis plays an important role on appropriately predicting the biomechanical behavior of the cervical spine segment.