Herniated Disc Definition



The herniated disc means part of the nucleus (N) pushes through the outer ring of the disc (A = Annulus). Herniation means displacement from its original location. The diagram shows the herniation in red. Compare the diagram on the left (normal disc) to the diagram on the right (herniated disc). In the normal disc, the nucleus (N) is completely surrounded by intact ring called the annulus (A). In the diagram on the right (herniated disc), the outer ring is torn, allowing the displacement of the nucleus.



The image above is a schematic of a top down view of the disc in the normal anatomic arrangement. Notice that immediately behind the disc is the dura (black ring) (dura = sack that contains spinal fluid and the nerves) and the nerve roots themselves (black arrows). If a disc herniates (pushes through the ring of the disc, the annulus), the nerves are easily effected because they are just behind the normal disc structure. The herniation usually occur towards the back of the disc because the wall of the ring (annulus) is thinner and the front side of the ring (annulus) is bordered by the strongest ligament in the spine. (the anterior longitudinal ligament)