disc herniation

Disc herniation refers to the displacement of intervertebral disc material beyond the normal confines of the disc but involving less than 25% of the circumference (to distinguish it from a disc bulge). A herniation may contain nucleus pulposus, vertebral endplate cartilage, apophyseal bone/osteophyte and annulus fibrosus.

Disc herniations can be divided into groups in a variety of ways. Commonly they are divided into protrusion vs extrusion:

  • protrusion
    • base wider than herniation
    • confined to disc level
    • outer annular fibers intact
  • extrusion
    • base (a.k.a. neck) narrower than herniation 'dome'
    • may extend above or below endplates or adjacent vertebrae
    • complete annular tear with passage of nuclear material beyond disc annulus
    • disc material can then migrate away from annulus or become sequestered

Herniations can further be classified as:

  • contained
  • not contained
    • tear of outer fibers of annulus fibrosus and posterior longitudinal ligament

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