The sciatic nerve is a large nerve that runs from the lower back down the leg and into the foot. Irritation, inflammation or compression of this nerve can lead to the development of sciatica--a condition typically characterized by radiating pain down the buttocks, thigh and lower leg. Conditions that cause a narrowing of the spinal column, slippage of vertebral bones or rupture of vertebral discs in the lower lumbar region can cause sciatica.
Piriformis Syndrome
Piriformis syndrome is a condition characterized by a tightening and spasm of the piriformis muscle--the muscle that connects the lower part of the spine to the femur, or thighbone, and helps rotate the hip. According to SpineUniverse, because the sciatic nerve is located just below the piriformis muscle, contractions can compress the nerve and cause sciatica. Sitting, lying down or remaining inactive for extended periods of time can cause piriformis syndrome, as can trauma due to accidents, falls or other injury, according to MayoClinic.com.
Vertebral Bone Conditions
Spondylolisthesis is a condition that occurs when a bone in the lower part of the spine slips forward and over the top of another spinal bone. According to MayoClinic.com, spondylolisthesis is usually caused by degenerative diseases of the vertebral discs. As a vertebra slips out of alignment, in may compress nearby nerves--including the sciatic nerve--and cause the development of sciatica.
According to the Merck Manuals, another bone condition that affects the spine and can cause sciatica is osteoarthritic osteophyte formation--bony deposits that form in areas where the spine has started to deteriorate from disease. These bony spurs can impinge upon and inflame nearby nerves, potentially causing associated sciatic nerve pain.
Lumbar Spinal Stenosis
Lumbar spinal stenosis--a condition characterized by a narrowing of the spinal passageway--is a common cause of sciatica affecting older people, according to SpineUniverse. The roots of spinal nerves pass through openings in the spine and then branch off to other parts of the body after leaving the spinal column. If the area within the spinal cavity narrows due to degeneration, injury or some other disease, compression on the nerve roots occurs. In some cases, people may experience symptoms of a pinched nerve only when sitting or standing in certain positions, or when walking or engaging in other active motion. According to MayoClinic.com, lumbar, sacral and sciatic nerves may become compressed when spinal stenosis occurs in the lumbar, or lower back, region.
Herniated or Bulging Disc
Conditions that affect the health of the vertebral discs in the lower back can lead to nerve compression and symptoms of sciatica. According to SpineUniverse, a bulging or completely herniated disc---a condition in which the inner material, or nucleus, of the disc pushes through its outer wall and into the spinal canal--can push directly on the sciatic nerve. In addition, the acidic fluid from inside the ruptured disc can leak out and cause additional nerve inflammation and bothersome symptoms of numbness or tingling and muscle weakness in the lower back and legs.
Tumors
Tumors that grow in or near the lumbar region of the spine can compress the sciatic nerve and cause the development of sciatica. According to MayoClinic.com, the sciatic nerve may become pinched when these growths form in between the spinal cord and vertebral disks, in the membranous tissue that coats the spinal cord or within the spinal cord itself. Both benign, or non-cancerous and malignant, or cancerous, tumors can cause sciatica when they are located near the bottom of the spine.
