annulus and nucleus

A vertebral disc consists of two parts. The inner area is the nucleus and outer area is the annulus. The nucleus, or inner core of the disc consists of a gelatinous material. The annulus (or outer ring) is the strongest portion of the disc….it keeps the nucleus from leaking out, supports the weight of the spine and prevents excessive motion. The annulus is built from layers of fibers. The disc can rupture when the fibrous covering the annulus is torn. The facet joints also help prevent excessive motions (facet joints and disc prevent movement, together called a motion segment) when there is a problem/excessive movement in the motion segment/wavering in the spine…makes it difficult to even stand up straight and can be very painful…the remedy may be bone fusion (which restricts movement).

Herniated Disc

herniated disc illustration

Shows the nucleus coming out of the annulus…and starts to press on the nerve (which causes pain). Others would call this a ruptured disc, but same idea. The pressure on the nerve will cause pain…and can cause other symptoms as well (restricted movement in other parts of the body…i.e. a herniated cervical disc (in neck) may, depending on location, cause pain or restricted movement in the arm (if that is where the nerve goes) or may impair bladder function.

herniated disc

Disc degeneration (can be caused by a number of things, but the nucleus is starting to protrude into the annulus…shows that the disc is not symmetrically round. Generally not from traumatic causes (i.e. age);

Prolapse (also called disc bulge and some will consider a prolapse the same as a herniation…especially when the bulge presses on a nerve);

Extrusion – herniation or rupture;

Sequestration – a severe rupture due to the nucleus spilling out into the spinal canal. In minor herniation, the nucleaus may come out, but may be contained within a tight area. As you can see there is plenty open to interpretation depending on the reader of the herniation.

Click on the link to read more generally about spine anatomy. For a more advanced discussion, read about modic changes and what they have to do with herniated discs.

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