Fig. 1.

Schematic representation of innervations and vascularization pattern in healthy and degenerate intervertebral disk. (A) Nerve fibers and blood vessels penetrate only the outer third of the AF in healthy disks with a high proteoglycan content. (B) Low oxygen levels, low glucose concentrations, end plate calcification, and adverse load contribute to an increased production of proteases, cytokines, and neurogenic and angiogenic factors resulting in matrix degradation and attraction of nerve fibers and blood vessels. (C) Nerve fibers and blood vessels penetrate deep into the degenerated disk as a result of the low proteoglycan content and the increased production of angiogenic and neurogenic mediators. Abbreviations: AF, annulus fibrosus; DRG, dorsal root ganglion; iAF, inner annulus fibrosus; NP, nucleus pulposus.