Annulus fibrosus
Each intervertebral fibrocartilage is composed, at its circumference, of laminæ of fibrous tissue and fibrocartilage, forming the annulus fibrosus.
Type I collagen accounts for nearly 70% of the dry weight of the outer annulus fibrosus (AF), with type II collagen gradually increasing and type I collagen decreasing from the outer to inner AF 1).
Each layer of the AF has an oriented collagen architecture, with adjacent lamellae alternating in fiber angles approximately 30° to the transverse plane of the disc 2).