Biomechanical effect of posterior elements and ligamentous tissues of lumbar spine on load sharing.

In this paper, we report on the development of a three-dimensional model of human lower lumbar spine based on actual geometry of L4-L5 motion segment. The simulation is performed on the model extracted from 2 mm slices of CT-Scan data of a healthy subject. The finite element model includes different parts, such as, cortical shell, cancellous core, endplates, pedicle, lamina, transverse process, and spinous process. Additionally, it takes into account the intervertebral disc including the nucleus pulposus and annulus fibrosus. The seven ligamentous structures of the L4-L5 motion segment, such as, anterior longitudinal ligament, posterior longitudinal ligament, and supraspinous ligament, were also incorporated. Various biomechanical characteristics of the computer generated model are studied under different physiological loadings. The focus of this study is on the role of posterior elements on load sharing of the lower lumbar region. The simulation yields data on the stress distribution inside the vertebrae and the amount of resulting deformation that takes place. Different simulated models of an injured lumbar spine are also being analyzed for two cases of facetectomy and degraded nucleus disorders. It is shown that the inclusion of the posterior elements along with the ligamentous tissues lead to an increase in the stiffness and stability of the L4-L5 motion segment.