Anatomy, physiology and pathophysiology of intervertebral discs - a review of the literature. Part I: Anatomy and physiology

In order to understand the degeneration of intervertebral discs, it is necessary to have knowledge on the physiology and anatomy of healthy intervertebral discs. In part I the current state of knowledge on the anatomy, biochemistry and physiology of inter vertebral discs will be presented and part II will deal with the fundamentals of the degeneration of intervertebral discs. Intervertebral discs age faster than nearly all other tissues because the nutrient supply is impeded due to the lack of vascularisation. The most important structural alterations in the degenerative process are decreases in water content and osmotic pressure, especially in the nucleus pulposus, the inner part of the annulus fibrosus, as well as wear of the matrix. The decreasing osmotic pressure strengthens the opening of existing tears despite a decrease in shearing forces in the annulus. Fibrous alterations of the nucleus, breakdown in structure of the annulus and alterations to the vertebral bodies and the end plates occur most commonly in the first two and in the fifth to seventh decades of life. The alterations are more severe in the lower than in the upper vertebral discs and precede the formation of fissures and tears. The time scale shows a strong correlation with fissures and tears which appear in the first decade of life. In contrast edge lesions arise independently from them and appear much later.