Degenerative Disc Disease I: Introduction

Each intervertebral disc contains two main components: the nucleus pulposus, a gel-like inner core rich in proteoglycans and water that resists compression and maintains disc height, and the annulus fibrosus, a tough outer ring of concentric collagen lamellae that provides tensile strength and contains the pressurized nucleus. Together, these structures enable the disc to absorb load and distribute forces throughout the spine.

Adult intervertebral discs are largely avascular and rely on passive diffusion of nutrients and waste products through the vertebral endplates. This avascular design means discs depend entirely on diffusion for nutrient supply, making them vulnerable to reduced transport when endplate function declines with age or disease.

Degenerative disc disease results from age-related biochemical and mechanical changes influenced by genetic predisposition, metabolic factors, and environmental stressors such as repetitive lifting. Alterations in nutrient supply, declining proteoglycan production, and mechanical stress impair matrix maintenance, accelerating degeneration over time.

Disc degeneration leads to disc height loss, bulging, and annular tears as the nucleus pulposus loses water and proteoglycans decline. In severe cases, herniation of nucleus material may compress nerve roots, causing radicular pain, or compress the spinal cord, potentially leading to increased intracranial pressure and neurological complications.

With aging, proteoglycan production declines significantly, reducing the disc's ability to retain water. Proteoglycans are hydrophilic molecules that bind water molecules; their decline directly decreases water content, which reduces elasticity, shock absorption capacity, and overall disc function in the nucleus pulposus.

No, degenerative disc disease 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. Structural changes may be present without causing pain or functional impairment.

Beyond aging, risk factors include genetic predisposition, diabetes, obesity, smoking, and repetitive mechanical stress from occupational activities such as lifting. These factors can accelerate the degenerative process by increasing metabolic demand, reducing nutrient availability, or imposing additional mechanical strain on disc structures.