Potential Causes of Sciatica

Common causes of sciatica are discussed below.

Lumbar herniated disc

Research suggests that up to 90% of sciatica is caused by a lumbar herniated disc. The herniated disc typically compresses one or more spinal nerve roots (L4-S3) that form the sciatic nerve.

A lumbar herniated disc can cause sciatica in two ways:

• Direct compression. Direct compression of the sciatic nerve can occur when a lumbar disc bulges (contained-disc-disorder) or when the soft inner material of the disc leaks out or herniates through the fibrous outer core (non-contained disc disorder) and presses against the nerve.
• Chemical inflammation. An acidic chemical irritant from the disc material (hyaluronan) may leak out and cause inflammation and irritation in the area around the sciatic nerve.

A herniated disc may compress the sciatic nerve on one side, causing symptoms in one leg, or the disc may bulge or herniate from both sides, causing symptoms in both legs (bilateral sciatica). Bilateral sciatica may also be caused by two adjacent segment discs herniating on either side, although this possibility is rare.

Degeneration

Degeneration of tissues in the lumbar spine can compress or irritate the sciatic nerve roots in several ways:

• Degeneration of the facet joints can cause the synovial tissue in the joint’s capsule to inflame and increase in bulk.
• Degeneration of vertebral bone may cause abnormal bone growths (bone spurs or osteophytes). These abnormally bulky tissues in the lumbar spine may cause compression of one or more nerve roots of the sciatic nerve.
• Degenerated intervertebral discs may secrete inflammatory proteins, causing inflammation of the sciatic nerve.

Depending on the severity, the nerve roots may cause varying symptoms in the low back and leg.

Lumbar spinal stenosis

Lumbar spinal stenosis is the narrowing of the spinal canal and is relatively common in adults older than age 60.⁸ Research suggests that lateral recess stenosis may be common in causing sciatica in the elderly population.

Spondylolisthesis

Spondylolisthesis occurs when a small stress fracture causes one vertebral body to slip forward on another.

For example, the L5 vertebra may slip forward over the S1 vertebra. Sciatica may result from nerve compression following the disc space collapse, fracture, and forward slipping of the vertebral body. Spondylolisthesis may cause bilateral sciatica and is more common in younger adults.

These conditions may develop over time or spontaneously due to trauma or physical stress injury. Motor vehicle accidents, sports injuries, or falls may cause direct injury to the sciatic nerve. Conditions such as spondylolisthesis and herniated discs may develop from physical stress injuries, such as from weightlifting.

Lower Back Conditions that Cause Sciatica-Like Symptoms

Some lower back conditions may cause sciatica-like symptoms. A few examples are discussed below.