The lumbar disc is a unique and well-designed structure in the spine. It is strong enough to resist terrific forces in multiple different planes of motion, yet it is still very mobile. The disc has several functions, including acting as a shock absorber between the vertebral bodies.
The lumbar disc has been likened to a jelly donut. It is comprised of a series of bands that form a tough outer layer and soft, jelly-like material contained within:
Annulus fibrosus—the disc’s firm, tough outer layer
Nerves to the disc space only penetrate into the very outer portion of the annulus fibrosus. Even though there is little innervation to the disc, it can become a significant source of back pain if a tear in the annulus reaches the outer portion and the nerves become sensitized. With continued degeneration, the nerves on the periphery of the disc will actually grow further into the disc space and become a source of pain.
Nucleus pulposus—the jelly-like inner disc material
The nucleus pulposus contains a great deal of very inflammatory proteins. If this inner disc material comes in contact with a nerve root, it will inflame the nerve root and create pain down the leg (sciatica or radiculopathy). In the same manner, if any of the inflammatory proteins within the disc space leak out to the outer annulus and touch the pain fibers in this area, it can create a lot of low back pain.
Source of the Pain
Generally, the pain associated with degenerative disc disease is thought to stem from two different factors:
- Abnormal micromotion instability
The proteins in the disc space can cause a lot of inflammation, and inflammation in the disc space can lead to low back pain radiating to the hips. The associated pain can also travel down the back of the legs.
In This Article:
If the annulus—the outer rings of the intervertebral disc - becomes damaged or worn down, it is not as effective in resisting motion in the spine. This condition has been termed “micromotion” instability because it is usually not associated with gross instability (such as a slipped vertebral body or spondylolisthesis).
Both the inflammation and micromotion instability can cause muscular spasm in the low back. The muscle spasm is the body’s attempt to stabilize the low back. It is a reflex, and although the body’s response of muscle spasm is not necessary for the safety of the nerve roots, it can be quite painful.