Nucleus pulposus

the central portion of the intervertebral disc, which at birth consists mainly of mucoid material and gradually becomes replaced by fibrocartilage. The nucleus fibrosus is surrounded by the anulus fibrosus (III:1).

This structure is the major site of abnormality in intervertebral osteo chondrosis. Dehydration and loss of tissue resiliency accompanying the ageing process lead to degeneration of the nucleus pulposus, which becomes desiccated and friable owing to loss of water and proteoglycans. Clefts appear within the nucleus and extend into the anulus fibrosus. On radiographs a vacuum phenomenon (or Knutson phenomenon) may also be seen in the nucleus pulposus.

In degenerative disease of the spine, chronic degenerative calcific deposits may occur in the nucleus pulposus and anulus fibrosus.

Intervertebral disc displacement represents a prolapse of discal material (nucleus pulposus) due to elevated intradiscal pressure producing tensile strains on the fibers of the anulus fibrosus and cartilaginous endplates.

Chemonucleolysis, a controversial technique in the treatment of discal herniation, makes use of chymopapain or collagenase injected into the intervertebral disc to cause temporary dissolution of the nucleus pulposus.