Intervertebral disc

Histological structure and development

When studying a histological slide of an intervertebral disc, it is important to consider that the section often captures adjacent parts of the vertebral bodies. This is usually embryonic material where ossification is not yet complete.

Vertebrae are formed via indirect (endochondral) ossification, like spongy and tubular bones. First, a cartilaginous model is formed from hyaline cartilage, which is then destroyed and replaced by bone tissue.

On the histological slide of the disc, one can observe:

• Elements of the disc itself: fibrocartilage, dense connective tissue, and nucleus pulposus.
• Elements of the vertebrae: hyaline cartilage and areas of indirect ossification — zones of contact between degenerating cartilage and forming bone trabeculae.

Anatomy and components of the disc

The intervertebral disc (discus intervertebralis) is part of the intervertebral symphysis (symphysis intervertebralis), which is a cartilaginous joint between vertebral bodies. Unlike synchondroses, which consist of continuous cartilage tissue, symphyses have a cleft-like space within the thickness of the cartilage. Previously, they were called "hemijoints": these are not diarthroses, but they provide greater mobility than a synchondrosis.

The intervertebral disc includes:

• Anulus fibrosus (anulus fibrosus) — concentric layers of fibrocartilage.
• Nucleus pulposus (nucleus pulposus) — a remnant of the notochord.

Hyaline cartilage plates are adjacent to the vertebral bodies.

Regional features and topography

The characteristics of the discs vary depending on the region of the vertebral column:

• Cervical region: discs are the thickest relative to the vertebral body.
• Thoracic region: discs are thinner; the intervertebral disc in the thoracic region is cited as an example of a permanent synchondrosis. An important anatomical landmark: the lower boundary of the trachea, i.e., its bifurcation, posteriorly corresponds to the intervertebral disc between the IV and V thoracic vertebrae. In the area of bifurcation, the depth is 6–12 cm.
• Lumbar region: discs are the most massive.
• Sacral region: intervertebral discs are temporary synchondroses. Over time, they gradually calcify and transform into synostoses.

Clinical significance: degeneration and compression

Degeneration of the intervertebral disc can lead to changes in the intervertebral foramina of the cervical spine $C_{II}$ – $C_{VII}$.

• Intervertebral foramen stenosis: narrowing of the lumen leads to compression of nerve roots and vessels. Normally, the intervertebral foramen transmits nerve roots (radices nervorum), an artery, and a vein, surrounded by adipose tissue.
• Deformation of the uncinate process (processus uncinatus): occurs as a consequence of degenerative processes in the intervertebral disc, further aggravating stenosis and compression of neural structures.
• C8 nerve root lesion: pain occurs in the C8 dermatome area, paresthesias, hypalgesia in the C8 dermatome innervation zone, weakness or paresis of hypothenar muscles, potential hypothenar muscle atrophy, diminished triceps reflex and Trömner's reflex.
• Intradural extramedullary tumors: most commonly originate from the meninges of adjacent posterior roots. They can grow in an "hourglass" shape extending into the spinal canal, growing through the intervertebral foramen and emerging outward. Early signs are radicular pain and paresthesias. As the tumor grows, compression of the posterior roots occurs, followed by compression of the spinal cord: primarily affecting the posterior funiculi, with secondary involvement of the pyramidal tract descending in the lateral funiculum. Rapidly progressive spastic paresis in the lower extremities, paresthesias with a sensation of cold, and ascending loss of epicritic and proprioceptive sensitivity are possible.

Class and exam questions

What else to study on this topic

• Intervertebral symphysis and types of bone connections
• Endochondral ossification of vertebrae
• Topography of the trachea and main bronchi
• Spinal nerve root lesion syndromes

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.