Sciatica refers to pain that radiates along the path of the sciatic nerve and its branches — from your back down your buttock and leg. The sciatic nerve is the longest nerve in your body. It runs from your spinal cord to your buttock and hip area and down the back of each leg.
Sciatica is a symptom, not a disorder. The radiating pain of sciatica signals another problem involving the nerve, such as a herniated disk. Depending on the cause, the pain of acute sciatica — which may be quite uncomfortable.
Your sciatic nerve branches from your spinal cord through your hips and buttocks and down the back of each leg. This nerve controls many of the muscles in your lower legs and provides feeling to your thighs, legs and feet. Sciatica may develop when a nerve root is compressed in your lower (lumbar) spine — often as a result of a herniated disk in your lower back.
Disks are pads of cartilage that separate the bones (vertebrae) in your spine. Filled with a gel-like substance, they keep your spine flexible and act as shock absorbers to cushion the vertebrae when you move.
If the outer covering of a disk tears (herniates), gel may seep out and press on a nerve root, causing pain in your back, leg or both. If the damaged disk is in the lower part of your back, you may also experience numbness, tingling or weakness in your buttock, leg or foot.
Although a herniated disk is a common cause of sciatic nerve pain, other conditions also can put pressure on your sciatic nerve, including:
Lumbar spinal stenosis. Spinal stenosis is a narrowing of one or more areas in your spine — most often in your upper or lower back. When the narrowing occurs in the lower spine, the lumbar and sacral nerve roots may be affected.
Spondylolisthesis. This condition, often the result of degenerative disk disease, occurs when one vertebra slips slightly forward over another vertebra. The displaced bone may pinch the sciatic nerve where it leaves your spine.
Piriformis syndrome. The piriformis muscle starts at your lower spine and connects to each thighbone (femur). Piriformis syndrome occurs when the muscle becomes tight or goes into spasms, putting pressure on the sciatic nerve. Prolonged sitting, car accidents and falls can contribute to piriformis syndrome.
Spinal tumors. In the spine, tumors can occur inside the spinal cord, within the membranes (meninges) that cover the spinal cord, or in the space between the spinal cord and the vertebrae. As it grows, a tumor compresses the cord itself or the nerve roots.
Trauma. A car accident, fall or blow to your spine can injure the lumbar or sacral nerve roots.
Sciatic nerve tumor or injury. Sometimes, the sciatic nerve itself may be affected by a tumor or injury.
Other causes. In some cases, your doctor may not be able to find a cause for your sciatica. A number of problems can affect your bones, joints and muscles, all of which could potentially result in sciatic pain.