Intervertebral discs are located between the vertebral bodies of C2/3 to L5/S1, totalling 23 in the conventional spine. Together they account for approximately 25% of the total height of the vertebral column. This decreases with age as disc height is lost.
They represent the hydro-mechanical system of load cushioning. Specifically, compressive forces act on the nucleus pulposus; on the annulus fibrosus tensile stresses prevail.
The upper thoracic discs are the thinnest and in general thoracic discs are the same width anteriorly as they are posteriorly. This is not the case in the cervical and lumbar spine, where greater thickness anteriorly contributes to the normal cervical and lumbar lordosis.
Each intervertebral disc is comprised of:
- peripheral annulus fibrosus
- central nucleus pulposus
- hyaline cartilage (vertebral side) and fibrocartilage (nucleus pulposus side)
Above and below the intervertebral disc are the vertebral body endplates. The inner layers of the annulus fibrosus and nucleus pulposus have neither innervation nor blood supply; they receive nutrition via diffusion across the vertebral body endplates. The outer fibers of the annulus fibrosus are innervated by sinuvertebral nerves arising from the dorsal root ganglia.