One of the most critical factors contributing to the degeneration of the central portion or nucleus of the disc is the loss of nutrition.  The cells within the center portion of the intervertebral disc are dependent the passive movement (diffusion) of nutrients through from the underlying bone adjacent to the cartilage through the end-plate in the disc.  The nutrients pass into the disc along with water.  Oxygen and nutrients are delivered to the adjacent bone through blood vessels that enter the bone.  Reduced nutritional support to the specialized cell population (chondrocytes) inside the disc reduces the discs capacity to heal, thereby promoting accelerated degeneration.  Any disorder which compromises blood flow to the vertebrae of the spine will contribute to the advancement of degenerative disc disease.  Contributing conditions in the elderly include peripheral vascular disease, vascular compression syndromes, blood clotting disorders (coagulopathy), chronic smoking, heart disease, kidney disease, and diabetes.

In addition to the loss of water content there are other age-related changes, which take place in the disc.  These age-related changes result in less capacity to move fluid and nutrients into disc during spinal movement.  The majority of degenerative changes initially occur within the center of the disc (nucleus pulposus) and along the transitional region between the center of the disc and the inner supportive (annular) fibers.  Supportive fibers of the intervertebral disc (collagen) increase in quantity, and change in quality. 

Research studies have also shown that cell types and the number of healthy cells change dramatically with age in the central portions of the intervertebral disc. 

Age-Related Vertebral End Plate Changes

The changes associated with aging affect the vertebral end plate and the adjoining intervertebral disc.  The breakdown and failure of the cartilage end plate affects the health of the adjacent disc.  The end-plate progressively becomes thinner with age and loses underlying bony support.  The thinning bone under the end-plate may fail leading to small fractures (microfractures).   The movement (passive diffusion) of nutrients and fluid into and out of the disc occurs at the disc-end plate interface.  The fluid exchange between the vertebral bodies and the adjacent disc occurs at the perforated end plate that acts as a semi-permeable membrane.  Most of the fluids flow through the central portion of the endplate, however, approximately 40% of the overall disc cartilage interface may be permeable to nutrients and fluid. The incidence of Schmorl’s nodes or endplate failure with disc migration at the adjacent bone increases with age and can be seen on X-rays, CT and MRI.