Low back pain is the second leading cause of doctor visits each year, afflicting over 65 million Americans. The precise cause of back pain is largely unknown, but degeneration of the intervertebral disc has been implicated as a possible source. It is known that disc degeneration begins with changes in the biochemical content of the nucleus pulposus. However, little is known about the mechanism by which degeneration progresses, leading to structural damage and tears in the annulus fibrosus.

The goal of this dissertation is to determine the mechanical effects of degeneration in the nucleus pulposus and to understand the role of the nucleus in disc mechanical function. The overarching hypothesis of this study, that degenerative changes in the nucleus lead to an altered loading state in the disc, causing increased deformation and strains in the annulus fibrosus, was investigated using mechanical experimentation and magnetic resonance imaging (MRI).

The earliest stages of disc degeneration occur in the nucleus pulposus, where there is a decrease in proteoglycan content and an increase in cross-linking of the tissue. A spin-lock pulse sequence, T]p MRI, is sensitive to these changes, suggesting the potential to diagnose early disc degeneration. Mechanical function of the nucleuspulposus is determined by its biochemical content:​ both proteoglycan loss and increased cross-linking affect the compressive behavior of the nucleus.

Partial removal of the nucleus pulposus results in increased range of motion during cyclic loading, highlighting the role of the nucleus in regulating disc deformation and range of motion. MR imaging and texture correlation, a pattern matching technique, can be used to track deformations and strains within the intervertebral disc.

Degeneration alters the biochemical content and compressive properties of the human nucleus pulposus. The use of quantitative T_1ρ-weighted MRI may allow earlier diagnosis of disc degeneration. The nucleus is shown to play an important role in regulating disc function and deformation. Texture correlation may be used to study the effects of degeneration on the deformation and strain within the intervertebral disc. Altered strains in the annulus fibrosus could be a potential mechanism for the progression of disc degeneration.