The sciatic nerve is the largest nerve in the body and is as big around as a human finger, according to Steven R. Garfin, M.D., professor and chair, Department of Orthopaedics at the University of California, San Diego. He explains the term sciatica as a way to describe pain traveling the length of the sciatic nerve. There are a variety of causes for this condition; knowing the specific cause helps doctors determine the correct treatment.
Lumbar Spinal Stenosis
Lumbar refers to the lower back, while spinal stenosis is a condition causing one or more areas of the spine to narrow. When the narrowing occurs in the lumbar area, both the lower back and its sacral roots are affected, the Mayo Clinic explains. The sacral roots are one of five pairs of roots that create the sciatic nerve.
Jean-Jacques Abitbol, M.D., an orthopaedic surgeon and contributing writer for the website Spineuniverse, adds that lumbar spinal stenosis primarily affects older people, and that its resulting pain is usually the result of certain positions or activities. These include standing or walking for long periods of time. Sitting down can relive the pain.
Herniated Disc
A herniated disc occurs when the center of a disc--the cushion between vertebrae--breaks through its outer wall. In the center of each disc is a gel-like substance; when a disc becomes herniated, this substance presses against the nerve root next to it, compressing the nerve, resulting in sciatica pain. As Abitbol explains, the effects of a herniated disc is worse than that of a bulging disc. This is because the substance inside the disc contains an acidic, chemical irritant that causes inflammation of the nerve. In addition to the pain, herniated discs often result in numbness of the extremities and muscle weakness.
Piriformis Syndrome
The Mayo Clinic health education website explains that the piriformis muscle begins at the lower spine and connects to each thighbone. Piriformis syndrome occurs when the muscle tightens or begins to spasm, placing pressure on the sciatic nerve. Because it is hard to detect with diagnostic imaging, such as an MRI or x-ray, diagnosing and treating this condition is difficult. Its most common causes include car accidents, falls and prolonged periods of sitting.
Spondylolisthesis
Abitbol says the most common disorder affecting the lumbar spine is spondylolisthesis, a condition resulting in a vertebra becoming displaced and slipping over the vertebra next to it. Spinal root compression occurs as a result, causing sciatic leg pain. Doctors categorize this condition as developmental; it is usually found at birth and continues to worsen throughout childhood. In some cases it can result from physical stress or trauma.
Spinal Tumors
While rare, the development of tumors on the spine can result in sciatic pain as the tumor compresses the nerve. The risk for sciatic pain exists only if the tumor develops in the lumbar region, according to Abitbol.
