The two sciatic nerves are the widest and longest nerves in the body. Each is almost as wide as a finger. On each side of the body, the sciatic nerve runs from the lower spine, behind the hip joint, down the buttock and back of the knee. There the sciatic nerve divides into several branches and continues to the foot. When the sciatic nerve is pinched, inflamed, or damaged, pain—sciatica—may radiate along the length of the sciatic nerve to the foot. Sciatica occurs in about 5% of people who have back pain. In some people, no cause can be detected. In others, the cause may be a herniated disk, irregular projections of bone due to osteoarthritis, spinal stenosis, or swelling due to a sprained ligament. Rarely, Paget disease of bone, nerve damage due to diabetes (diabetic neuropathy), a tumor, or an accumulation of blood (hematoma) or pus (abscess) causes sciatica. Some people seem to be prone to sciatica. Sciatica usually affects only one side. It may cause a pins-and-needles sensation, a nagging ache, or shooting pain. Numbness may be felt in the leg or foot. Walking, running, climbing stairs, straightening the leg, and sometimes coughing or straining worsens the pain, which is relieved by straightening the back or standing. Often, the pain goes away on its own. Resting, sleeping on a firm mattress, taking over-the-counter acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs), and applying heat and cold may be sufficient treatment. For many people, sleeping on their side with the knees bent and a pillow between the knees provides relief. Stretching the hamstring muscles gently after warming up may help. Occasionally, other treatments are used, depending on the cause of sciatica. Treatments may include physical therapy, corticosteroids injected into the back, anticonvulsants, tricyclic depressants, and, for severe and persistent pain, surgery.