Anatomy and pathophysiology of intervertebral disc disease

Intervertebral discs provide support and cushioning against mechanical loads. Changes secondary to aging and degeneration lead to loss of this important function. This also sets the stage in some for disc-related pain. Various therapeutic modalities have been attempted with minimal long-term success to alleviate the poorly described disc-related pain. To better understand the pain originating from the disc, this article attempts to explore the anatomy of the disc and the different perturbations that occur following aging and degeneration. There is a great deal of similarity among the discs in different levels. They all consist of a nucleus pulposus, surrounded by the annulus fibrosus, whose outer layers integrate with the endplate and the ligaments to strengthen and provide support. The spinal arteries provide the nutrient supply, and the lack thereof seems to be a hallmark of degeneration and aging. The nerve supply is provided by the sympathetic chain and from the recurrent sino vertebral nerve, but only the outermost layers of the annulus contain the sensory nerve fibers. There also appears to be some genetic variation in the rate and degree of synthesis and breakdown in the primary structural components of the disc, increasing the predisposition for disc-related pain. This review will also briefly discuss the evidence that has accumulated regarding the occurrence of such pathologic changes from a genetic and ergonomic perspective.