Degenerative Disc Disease I: Introduction

Degenerative disc disease is a chronic condition in which intervertebral discs gradually lose structure and function. It is not infectious or autoimmune; rather, it results from age-related biochemical and mechanical changes, influenced by genetic, metabolic, and environmental factors.

Structure and Function of Discs

The spine contains 23 intervertebral discs that absorb load, distribute forces, maintain spacing, and allow flexibility. Each disc consists of a nucleus pulposus, a gel-like core rich in proteoglycans and water that resists compression and maintains disc height. Annulus fibrosus is a collagen-rich outer ring that provides tensile strength and stability. Sharpey’s fibers anchor the disc to the vertebrae, while ligaments add support. Disc composition varies: the nucleus contains more water and proteoglycans, while the annulus contains more collagen.

Disc Degeneration

Adult discs are largely avascular, relying on diffusion through the vertebral endplates for nutrient supply. Reduced transport decreases cell activity, disrupts matrix maintenance, and accelerates degeneration. With aging, proteoglycan production declines, reducing water retention, elasticity, and shock absorption.

Structural Changes and Effects

Degeneration leads to disc height loss, bulging, and annular tears. Herniation of nucleus material may compress nerve roots, causing radicular pain, or compress the spinal cord in severe cases.

Risk Factors and Clinical Relevance

Aging is the primary factor, but genetics, diabetes, obesity, smoking, and repetitive mechanical stress also contribute. Importantly, disc degeneration may be asymptomatic. Importantly, disc degeneration does not always cause symptoms. Imaging studies show that even pain-free young adults can have disc degeneration or bulging on MRI, especially in the lumbar spine.