Intervertebral disc

a type of symphysis or cartilaginous joint located between vertebral bodies in the spine. At the upper and lower aspects of the vertebral bodies are central depressions covered with hyaline cartilage (endplate), to which the intervertebral discs adhere. The disc consists of an inner, eccentrically located nucleus pulposus surrounded by a peripheral anulus fibrosus that unites the vertebral bodies firmly. A strong attachment between anulus fibrosus and vertebral body, termed Sharpeys fibres, occurs at sites of intramembranous ossification, blending with the periosteum. Anterior and posterior longitudinal ligaments attach to both vertebral bodies and discs. Also, see intervertebral disc.

2. Pathology

Numerous musculoskeletal diseases may affect the intervertebral discs.

Degenerative diseases involving the intervertebral disc include lengthening and weakening of the fibres in the anulus fibrosus and loss of water and protein from the nucleus pulposus. Rupture of the anular fibers may occur allowing the nucleus pulposus to herniate. Myelography may reveal a double density sign when the spine is viewed in the lateral projection after opacification of the dural sac. Retention of a herniated nucleus pulposus fragment behind the posterior longitudinal ligament is called a subligamentous herniation. A herniated fragment that has penetrated the posterior longitudinal ligament as well is called a sequestered fragment. Less extensive posterior displacement of the nucleus pulposus often is referred to as a discal protrusion or extrusion, although there is no consensus regarding such terrminology. Currently many authorities suggest that the term discal herniation is inappropriate and not specific.

Intervertebral disc displacement may occur if the nucleus pulposus is subjected to elevated pressure, causing it to prolapse from its confined space. The disc may be displaced anteriorly and laterally (spondylosis deformans), posteriorly or posterolaterally (intraspinal or intraforaminal herniation) or superiorly and inferiorly (Schmorls node). Schmorl's nodes occur not only in intervertebral osteo chondrosis but also in other disease processes that weaken or disrupt the endplate or subchondral bone, such as trauma, infection, osteoporosis, neoplasm, hyperparathyroidism and juvenile kyphosis. Displacement of disc material in a posterior or posterolateral direction is of great clinical significance because of the intimate relationship between the intervertebral disc and important neurologic structures. Various forms of posterior displacement are recognized:

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