Biomechanics of the anulus fibrosus and nucleus pulposus of the human lumbar intervertebral disc and the effects of degeneration

This dissertation provides an investigation and review of the material behavior of the anulus fibrosus and nucleus pulposus of the human lumbar intervertebral disc. The information, analyses, and conclusions of the studies presented reveal a new picture of the function and failure of the non-degenerate and degenerate intervertebral disc and provide a foundation which is necessary for accurate modeling of the disc.;A comprehensive series of studies on the mechanical behavior of the anulus fibrosus in tension is given. First, the tensile properties of single layer specimens of anulus are determined as a function of location within the disc to evaluate the behavior of the basic tensile structural unit of the highly organized anulus fibrosus. This is followed by a similar study on the tensile behavior of multiple layer samples which provides information regarding the interactions between each layer and anisotropy of the composite anulus. The effects of disc degeneration and aging on the tensile properties of the anulus fibrosus are also investigated to obtain a relationship between the morphological changes occurring in the anulus with degeneration and changes in its mechanical behavior.;The compressive behaviors of the anulus fibrosus under large deformations are also investigated. These material behaviors are described using a nonlinear biphasic mixture theory to evaluate the interactions between solid and fluid phases of the anulus. The effect of specimen orientation on these compressive material properties is also studied in order to evaluate the anisotropy of the anulus in confined compression. The results of this study are necessary for future modeling of the intervertebral disc with important implications for nutritional pathways.;The variety and polydispersity of the biomacromolecules comprising the nucleus pulposus gives rise to unique viscoelastic material behaviors. This dissertation investigates several forms for the relaxation spectrum in a viscoelastic model in order to obtain a model capable of describing the predominant viscoelastic behaviors of the non-degenerate and degenerate nucleus pulposus in shear. This study provides the first comprehensive series of tests on the load-deformation behavior of the nucleus pulposus.