Project overview:
The degenerated disc is believed to be the cause of lower back pain in 90% of spine surgeries. The
associated costs with degenerative disc disease is over $100 billion per year in the United States
alone. Therefore the intervertebral disc has been the subject of many studies. These studies have not
only helped to understand disc degeneration but also the functional mechanics of the components
that make up the intervertebral disc.
It was seen that the core of adult human intervertebral discs, the nucleus pulposus, is rich in
proteoglycans which make it swell with water. This core is constrained, in part, by the outer fibrous
layers of the intervertebral disc, the annulus fibrosus. This combination of a poroelastic core and
viscoelastic jacket behaves similar to an air filled tire, providing shock absorption and dissipation of
loads on the spine.
It is known that many other animal species exist whose intervertebral discs do not degenerate. Many
such species contain an other type of nucleus pulposus rich in notochordal cells with relatively little
extracellular matrix. These unqiue cells contain large vacuoles containing filled with aqueous
material. Although the structure of the notochordal rich and notochordal poor nucleus pulposus is
different both nuclei and intervertebral discs provide the same function. In contrast to the
notochordal poor nucleus, the mechanics of the notochordal rich nucleus pulposus is not well
understood, and such knowledge may help us to understand the role of mechanics in disc
degeneration.The goal of this study is to determine and compare the shear and compressive
properties of the nucleus for a notochordal-rich and –poor nucleus pulposus and thereby compare
their mechanics.