(See also Overview of Sports Injuries.)
The piriformis muscle extends from the pelvic surface of the large triangular bone at the base of the spine (sacrum, or tailbone) to the bony bump (trochanter) at the upper end of the thighbone (femur). During running or sitting, this muscle can compress the sciatic nerve at the site where it emerges from under the piriformis to pass over the hip rotator muscles. Piriformis syndrome is uncommon.
A chronic nagging ache, pain, tingling, or numbness starts in the buttocks and can extend down the entire back of the thigh and calf, and sometimes into the foot. Pain worsens when the piriformis is pressed against the sciatic nerve (for example, while sitting on a toilet, a car seat, or a narrow bicycle seat or while running).
People should temporarily stop doing any activity that causes pain. If pain is aggravated by sitting, people should stand or, if unable to do so, change positions to remove the source of pressure around the buttock. Specific stretching exercises for the posterior hip and piriformis can be helpful. Nonsteroidal anti-inflammatory drugs (NSAIDs) or other analgesics are used to relieve pain. Sometimes doctors inject a corticosteroid near the site where the piriformis muscle crosses the sciatic nerve to provide temporary pain relief. Surgery is rarely needed.