Intervertebral Disc Degeneration

The human spine consists of 23 intervertebral discs adjoining the vertebral bodies. These discs provide mechanical support and spinal motion and function to distribute loads from daily activities. Tissues of intervertebral discs share similarities to those of diarthrodial joints, such as a thin layer of cartilage that lines the interface between the joint and the bony elements and a central space rich in extracellular matrix molecules that promotes lubrication and maintains osmotic pressure. Like the pathophysiology of other cartilaginous joints, intervertebral discs undergo biomechanical and structural changes as a result of aging and mechanical insults. Due to higher mechanical loading, lumbar discs are more susceptible to degeneration, which can lead to symptomatic outcomes such as low back pain, sciatica, and other physical disabilities. These affect quality of life as we age and present a significant burden to the healthcare system globally. The etiology of intervertebral disc degeneration is not fully understood, but is a consequence of the changing structure and environment of its three interconnecting components, the nucleus pulposus, the annulus fibrosus, and the cartilaginous endplate, which function cooperatively to transmit load and regulate the cellular, biochemical, and nutritional properties of the disc. Abnormal changes in one or more of these disc compartments will compromise disc integrity and culminate in a degenerated disc state. Mechanistic insights into disc pathology can be gained through an understanding of the development and homeostasis of the intervertebral disc tissues. This chapter will provide an overview of the intervertebral disc in health and disease.