Histological Age Changes in the Anulus Fibrosus of the Human Intervertebral Disk

Abstract

The anulus fibrosus of the human intervertebral disk shows radical alterations both in texture and polysaccharide distribution in the course of aging. In young adults the anulus consists of dense fibrocartilage, arranged in concentric lamellae in which the collagen fibres run alternating courses; the intercellular component stains strongly and diffusely both with Alcian Blue and the P.A.S. method. The P.A.S.-reactive granular substance is identical with the brown aging pigment. The change in the P.A.S.-reactive component is interpreted as the freeing from a binding to collagen of a component containing protein and neutral carbohydrate and which is essential for the maintenance of normal tissue integrity. It is argued that a determining factor in these regressive changes is the alteration in the mechanical situation as a result of the gradual solidification of the nucleus pulposus. As a consequence of this alteration the anulus becomes subjected to pressure rather than to a tangential traction in the direction of the composing fibres.