A spinal disc herniation (prolapsus disci intervertebralis),
informally and misleadingly called a "slipped disc", is a
medical condition affecting the spine, in which a tear in the
outer, fibrous ring (annulus fibrosus) of an intervertebral disc
(discus intervertebralis) allows the soft, central portion
(nucleus pulposus) to bulge out. Tears are almost always
posterior-ipsilateral in nature owing to the presence of the
posterior longitudinal ligament in the spinal canal. This tear
in the disc ring may result in the release of inflammatory
chemical mediators which may directly cause severe pain, even in
the absence of nerve root compression (see "chemical
radiculitis" below). This is the rationale for the use of anti-
inflammatory treatments for pain associated with disc
herniation, protrusion, bulge, or disc tear. It is normally a
further development of a previously existing disc protrusion, a
condition in which the outermost layers of the annulus fibrosus
are still intact, but can bulge when the disc is under