A three-dimensional parameterized finite element model of the lower cervical spine. Study of the influence of the posterior articular facets.

In this study, we present a three-dimensional geometrical and mechanical finite element model of the complete lower cervical spine. The geometry of the vertebrae is parameterized which allows the model to fit different morphologies of vertebrae. The results obtained with a reduced functional unit model (without posterior arch) and with a complete functional unit model were compared with those obtained from experimental studies, when moments of flexion, extension lateral flexion and axial torque were applied. General agreement was observed. Since the model was parameterized, it was possible to study the influence of some geometrical parameters on the mechanical behavior of the cervical spine. Particularly, we focused on the influence of the posterior articular facets as their geometry is very different from those of the other spinal levels and as large inter-individual variability can be observed. The orientation of the facets with regard to the horizontal plane appeared to have a large influence on the 'coupled rotation to principal rotation' ratio, notably in lateral flexion.