Facet joints appear to have a major role in the mechanical behaviour of the spine and the thorax. In order to quantify their role and to represent with precision their behaviour, a previously existing finite element model of the global spine and thorax was improved. The input geometry to the model was obtained using a method which includes stereoradiographic 3-D reconstructions of a given patient as described in the joined paper of Aubin et al.. Zygapophyseal facets were parametrized using simple surface shapes (plane or cylinder) and were modelled by shell, point-to-surface contact and cable elements. Posterior arch and ligaments were also represented. Mechanical and geometrical properties necessary to complete the model were taken from. Geometric and material non-linearities were taken into account. Simulations were done on functional units as well as lumbar segments extracted from the model and results were compared to experimental data. Adequation of results was found, which supports the modelling method. However, further simulations are still in progress on global segments to complete the validation.