Healthy intervertebral discs contain approximately 80% water at birth, providing essential shock absorption between vertebrae. Over time, disc cells lose their ability to retain moisture and produce new proteoglycans — the molecules responsible for drawing water into the disc nucleus. By age 60, disc water content can decline to less than 70%, significantly reducing cushioning capacity.
As discs lose hydration, they flatten and become less flexible, narrowing the space between vertebrae. This height loss places abnormal stress on the facet joints and surrounding ligaments, triggering inflammation and pain signals. The once-smooth disc surface develops small tears in the outer annulus fibrosus, which can irritate nearby spinal nerves.
Simultaneously, the reduced disc height alters spinal biomechanics. Adjacent vertebral segments compensate by bearing more load, accelerating wear in neighboring discs. This cascade effect explains why many patients with DDD develop multi-level involvement over time, particularly in the lumbar (L4-L5, L5-S1) and cervical regions.
