What is piriformis syndrome?

Piriformis syndrome is a rare neuromuscular disorder that occurs when the piriformis muscle compresses or irritates the sciatic nerve-the largest nerve in the body. The piriformis muscle is a narrow muscle located in the buttocks. Compression of the sciatic nerve causes pain-requently described as tingling or numbness-in the buttocks and along the nerve, often down to the leg. The pain may worsen as a result of sitting for a long period of time, climbing stairs, walking, or running.

This answer is based on source information from the National Institute of Neurological Disorders and Stroke.

The piriformis is a very small, deep muscle that extends from the side of the sacrum (lowest backbone, tailbone) to the top of the thighbone at the hip joint, passing over the sciatic nerve.

Piriformis syndrome occurs when a short or tight piriformis is stretched to compress and irritate the sciatic nerve, causing the pain of sciatica. Referred pain from the piriformis is felt in the sacrum, buttocks, and hip.

A tight piriformis muscle can also put pressure on the pudendal nerve and cause pain in the groin, genitals, or rectum. In severe cases, piriformis syndrome could be responsible for buttock atrophy. The pain can cause altered gait and guarding, which can cause development of secondary musculoskeletal difficulties. Treatment of piriformis syndrome calls for releasing the entrapped sciatic nerve.