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The aim of this work is to understand the biomechanical behaviors of vertebra, intervertebral disc, ligament and facet joint. In view of biomechanics, the spinal motion segments are porous and solid-fluid interactive tissue structures and swelling pressure may be produced as a result in the intervertebral disc when under loading. The relationships of loading and displacement almost were linear in previous literature. However, published experimental data revealed that the response of large loadings corresponded closely with geometrical nonlinearity. A rather fine and efficient poroelastic finite element model of spinal motion segments is constructed for the purpose of simulating the complicated porous tissue structures/geometry of human lumbar spine. The FEM includes complicated L4/L5 porous tissue structures, nucleus pulpous, annulus fiber, seven nonlinear ligaments and non-thickness contact elements that were developed to simulate the compressive behavior of facet joints. The analytical process also offers an additional method with the approach from geometrical nonlinearity.