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:
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base wider than herniation
confined to disc level
outer annular fibers intact
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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:
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contained
with intact outer fibers of annulus fibrosus and posterior longitudinal ligament, or
with intact posterior longitudinal ligament alone
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not contained
tear of outer fibers of annulus fibrosus and posterior longitudinal ligament
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