Nonlinear analysis of intervertebral disk under dynamic load.

This study pertains to the response of intervertebral joint under dynamic axial load. The numerical model represents two vertebral bodies with an interposed disk and uses three-dimensional elements. A transversely isotropic material law is adopted for cortical bone and an isotropic law for cancellous bone. Annulus collagen fibers are modelled using truss elements with no compressive resistance. The disk material is assumed hyperelastic, using a mixed finite element approach, allowing a representation of the disk involving the incompressibility characteristics for the material. The analysis considers finite displacement and strain fields under dynamic load. Intensity, trend and distribution of loads on the vertebral body are deduced from the literature. The problem is investigated with reference to different compressibility levels of disk material related to disk degenerationn phenomena.