ABSTRACT
Objective In order to probe the possible biomechanical mechanism of lumbar vertebral injuries, we studied the nonlinear stress distribution on lumbar vertebrae at 1500N axial compression force and 15Nm bending moments during hambar flexion, extension, lateral bending and axial torsion using an available nonlinear finite element (FE) model of functional spine unit. Methods Three-dimensional nonlinear FE model was created based on CT data of L3-L4 motion segment. The segment mechanical responses to different loadings were evaluated by the range of disc bulging, the stress level of fibrousrings, facet loadings and equivalent stress distribution of posterior structure. Results Compression and flexion induced disc bulging in anterior region, whereas extension and lateral bending induced disc bulging posteriorly and posterolaterally. Axial torsion caused not only higher unilateral facet stress but also the concentrated stress on posteroleteral fibrousrings stress. The loadings in extension and axial compression were lower than in torsion but higher than in lateral bending and anterior flexion. Higher equivalent stress was found when compression and extension loadings were applied to the pedicle of vertebral arch and interarticularis. Conclusion Intervertebral disc beared higher compressive than tensile. The posterolateral regions of lumbar vertebrae were prone to be deformity and at higher risk of fibrousring failure. Stress failure could be occured when facets were overloaded with axial torsion,extension and extension force due to the importance of facets during lumbar movement.