THE MECHANICAL-BEHAVIOR OF BONY END-PLATE AND ANNULUS IN PROLAPSED DISC CONFIGURATION

The mechanical response of intervertebral joints is deeply influenced by disc degeneration. The phenomenon is expressed in terms of variatio ns in the biomechanical Properties of the material, whose compressibil ity characteristics change because of the liquid content loss in the t issue and, what is even more important, to prolapse. In this work, the problem is investigated by means of a computational mechanics approac h; a coupled material and geometric non-linear model is developed, rep resenting vertebra, annulus and nucleus submitted to an axial load. A transversely isotropic law is assumed for cortical bone in the vertebr al body and an isotropic law for the cancellous portion; a hyperelasti c formulation is assumed for the disc, allowing effective interpretati on of the mechanical characteristics of degeneration. The results obta ined are reported with regard to bony endplate and annulus behaviour; interaction phenomena between bony endplate and nucleus are emphasized .