Several lumbar spine (lower back) disorders can cause sciatica. Sciatica is often described as mild to intense pain in the left or right leg. Sciatica is caused by compression of one or more of the 5 sets of nerve roots in the lower back. Sometimes doctors call sciatica a radiculopathy. Radiculopathy is a medical term used to describe pain, numbness, tingling, and weakness in the arms or legs caused by a nerve root problem. If the nerve problem is in the neck, it is called a cervical radiculopathy. However, since sciatica affects the low back, it is called a lumbar radiculopathy.

Pathways to Sciatic Nerve Pain
Five sets of paired nerve roots in the lumbar spine combine to create the sciatic nerve. Starting at the back of the pelvis (sacrum), the sciatic nerve runs from the back, under the buttock, and downward through the hip area into each leg. Nerve roots are not "solitary" structures but are part of the body's entire nervous system capable of transmitting pain and sensation to other parts of the body. Radiculopathy occurs when compression of a nerve root from a disc rupture (herniated disc) or bone spur (osteophyte) occurs in the lumbar spine prior to it joining the sciatic nerve.

What Causes Sciatic Nerve Compression?
Several spinal disorders can cause spinal nerve compression and sciatica or lumbar radiculopathy. The 6 most common are:

• a bulging or herniated disc
• lumbar spinal stenosis
• spondylolisthesis
• trauma
• piriformis syndrome
• spinal tumors

Common Sciatica Cause #1: Lumbar Bulging Disc or Herniated Disc

A bulging disc is also known as a contained disc disorder. This means the gel-like center (nucleus pulposus) remains "contained" within the tire-like outer wall (annulus fibrosus) of the disc. 

A herniated disc occurs when the nucleus breaks through the annulus fibrosus. It is called a "non-contained" disc disorder. Whether a disc bulges or herniates, disc material can press against an adjacent nerve root and compress delicate nerve tissue and cause sciatica.

The consequences of a herniated disc are worse. Not only does the herniated disc cause direct compression of the nerve root against the interior of the bony spinal canal, but the disc material itself also contains an acidic, chemical irritant (hyaluronic acid) that causes nerve inflammation. In both cases, nerve compression and irritation cause inflammation and pain, often leading to extremity numbness, tingling, and muscle weakness.

Common Sciatica Cause #2: Lumbar Spinal Stenosis

Spinal stenosis is a nerve compression disorder most often affecting older adults. Leg pain similar to sciatica may occur as a result of lumbar spinal stenosis. The pain is usually positional, often brought on by activities such as standing or walking and relieved by sitting down. 

Spinal nerve roots branch outward from the spinal cord through passageways called neural foramina comprised of bone and ligaments. Between each set of vertebral bodies, located on the left and right sides, is a foramen. Nerve roots pass through these openings and extend outward beyond the spinal column to innervate other parts of the body. When these passageways become narrow or clogged causing nerve compression, the term foraminal stenosis is used.

Common Sciatica Cause #3: Spondylolisthesis

Spondylolisthesis is a disorder that most often affects the lumbar spine. It is characterized by one vertebra slipping forward over an adjacent vertebra. When a vertebra slips and is displaced, spinal nerve root compression occurs and often causes sciatic leg pain. Spondylolisthesis is categorized as developmental (found at birth, develops during childhood) or acquired from spinal degeneration, trauma or physical stress (eg, lifting weights). 

Common Sciatica Cause #4: Trauma

Sciatica can result from direct nerve compression caused by external forces to the lumbar or sacral spinal nerve roots. Examples include motor vehicle accidents, falling down, football and other sports. The impact may injure the nerves or, occasionally, fragments of broken bone may compress the nerves. 

Common Sciatica Cause #5: Piriformis Syndrome

Piriformis syndrome is named for the piriformis muscle and the pain caused when the muscle irritates the sciatic nerve. The piriformis muscle is located in the lower part of the spine, connects to the thighbone, and assists in hip rotation. The sciatic nerve runs beneath the piriformis muscle. Piriformis syndrome develops when muscle spasms develop in the piriformis muscle thereby compressing the sciatic nerve. It may be difficult to diagnose and treat due to the lack of x-ray or magnetic resonance imaging (MRI) findings. 

Common Sciatica Cause #6: Spinal Tumors

Spinal tumors are abnormal growths that are either benign or cancerous (malignant). Fortunately, spinal tumors are rare. However, when a spinal tumor develops in the lumbar region, there is a risk for sciatica to develop as a result of nerve compression. 

If you think you have sciatica, call your doctor. The first step toward relieving pain is a proper diagnosis.