Pain that radiates from one buttock down the back of the thigh while a person is seated is commonly caused by sciatica, according to WebMD. Sciatica is a symptom of impingement or irritation of the sciatic nerve, which extends from the lower spine into the legs.
Sciatica can be painful but it is not a sign of nerve damage unless the symptoms include weakness in the lower legs, numbness in the upper thighs or loss of bladder and/or bowel control, according to WebMD. In addition to nerve-root irritation, sciatica can be caused by lumbar stenosis, which is a narrowing of the lower part of the spinal canal; degeneration of a vertebral disc; spondylolisthesis or slipped disc; and pregnancy. Other risk factors include being overweight, lack of exercise, wearing high heels or sleeping on a mattress that doesn't provide enough support.
Sciatica usually responds to conservative treatments such as cold packs to reduce swelling during the initial period, heating pads after the first few days, stretching exercises and non-prescription pain relievers, states Mayo Clinic.
Bed rest is not recommended, and patients are advised to resume their daily activities within a few days, according to MedlinePlus. If conservative treatment fails to relieve the pain, a doctor may prescribe injections to reduce nerve inflammation.