Causes

Causes

In about 85% of back pain cases, the origin of the pain is unknown and even imaging studies usually fail to determine the cause. Disk herniation and disk degeneration due to aging are the most common causes of low back pain. Other problems can also cause this pain, however.

Lumbar Degenerative Disk Disease

Over the years, the disk can degenerate and produce low-grade inflammation and irritation. This age-related condition is a major source of chronic low back pain.

Herniated Disk and the Inflammatory Response

A herniated disk, sometimes, but incorrectly, called a slipped disk, is widely held to be the most common cause of severe back pain and sciatica. A disk in the lumbar area becomes herniated when it ruptures or thins out and degenerates to the point that the gel within the disk (nucleus pulposus) pushes outward. This event can take many forms.

• A bulge -- The gel has been pushed out slightly from the disk and is evenly distributed around the circumference.
• Protrusion -- The gel has pushed out slightly and asymmetrically in different places.
• Extrusion -- The gel balloons extensively into the area outside the vertebrae or breaks off from the disk.

There is some debate, however, about how pain develops from a herniated disk and how frequently it causes low back pain. Many people have disks that bulge or protrude and do not suffer back pain. Extrusion (which is less common than the other two conditions) is highly associated with back pain, since the gel is likely to extend out far enough to press against the nerve root, most often the sciatic nerve. Extrusion is very uncommon, however, and sciatic and low-back pain is very common suggesting that there are other, more prominent causes of this pain.

Ordinarily, at the time of any injury, the immune system triggers key factors that are designed to promote healing. Evidence is now pointing to an abnormal and persistent immune response in the cells of the nucleus pulposus that may be responsible for nerve injury and pain in the lower back. In such cases, the nucleus pulposus in the herniated disk overproduces certain factors known as cytokines -- notably tumor necrosis factor (TNF) -- that, in high levels, cause inflammation and cell damage. Evidence now suggests that such cytokines cause a biochemical reaction in the regions surrounding the bulging or protruded nucleus pulposus, which results in pain.