Sciatica

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Causes and Risk Factors

Sciatica results from inflammation, irritation, or compression of the sciatic nerve or nerve root (i.e., base of the nerve at the spinal cord). The most common cause for sciatica is intervertebral disc damage in the lumbar or sacral region of the spine (i.e., the lower back).

The spine or backbone is comprised of 33 bone segments called vertebrae. Vertebrae are arranged in a vertical column and held together by ligaments, which are attached to muscles by tendons.

Intervertebral discs are gel-like cushions located between each vertebra. They consist of semi-fluid matter (nucleus pulposus) surrounded by a capsule of elastic fibers (annulus fibrosus). When certain conditions (e.g., ruptured disc, herniated disc, slipped disc) occur in the lumbar or sacral region of the spine, the sciatic nerve root can become compressed, resulting in sciatica.

Sciatica also may be caused by wear and tear on the vertebrae (e.g., lumbar 5 [L5], sacral 1 [S1]) that results in pressure on the sciatic nerve root. The effects of aging and degenerative disc disease (osteoarthritis) can damage vertebrae.

Other conditions that may cause sciatic nerve inflammation or compression and lead to sciatica include the following:

• Injury (e.g., fractured pelvis)
• Pinched nerve (pressure from surrounding bone, cartilage, muscles, or tendons)
• Piriformis syndrome (caused by tightening or spasm of the piriformis muscle in the buttock)
• Spinal stenosis (narrowing of the spinal column)
• Spondylolisthesis (condition in which one vertebra slips forward and out of line; may occur as a result of damage to the vertebra [e.g., degeneration, spondylolysis] or spinal defects [e.g., spinal bifida])

In rare cases, sciatica may be caused by a benign tumor or cyst, or by cancer that has spread (metastasized), or by degeneration (deterioration) of the sciatic nerve root. The condition also may be idiopathic (i.e., occur without a known cause).

Several factors can increase the risk for sciatica. Some of these factors cannot be controlled (called unmodifiable risk factors) and some can be avoided (called modifiable risk factors).

Risk factors for sciatica include the following:

• Age (sciatica is more common between 30 and 50 years of age)
• Diabetes (increases the risk for nerve damage)
• Genetics (e.g., inherited spine abnormalities)
• Menopause (ending of menstrual periods in women; may lead to bone loss)
• Physical activities that involve heavy lifting or twisting the back (e.g., golf)
• Sedentary (inactive) lifestyle, including occupations that require sitting for long periods of time

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