Sciatica is pain in the lower extremity resulting from irritation of the sciatic nerve. The pain of sciatica is typically felt from the low back (lumbar area) to behind the thigh and can radiate down below the knee. The sciatic nerve is the largest nerve in the body and begins from nerve roots in the lumbar spinal cord in the low back and extends through the buttock area to send nerve endings down the lower limb. The pain of sciatica is sometimes referred to as sciatic nerve pain.
While sciatica is most commonly a result of a lumbar disc herniation directly pressing on the nerve, any cause of irritation or inflammation of the sciatic nerve can produce the symptoms of sciatica. This irritation of nerves as a result of an abnormal intervertebral disc is referred to as radiculopathy. Aside from a pinched nerve from a disc, other causes of sciatica include irritation of the nerve from adjacent bone, tumors, muscle, internal bleeding, infections in or around the lumbar spine, injury, and other causes. Sometimes sciatica can occur because of irritation of the sciatic nerve during pregnancy.