Piriformis syndrome is a condition in which the piriformis muscle, located in the buttock region, spasms and causes buttock pain. The piriformis muscle can also irritate the nearby sciatic nerve and cause pain, numbness and tingling along the back of the leg and into the foot (similar to sciatic pain).
The pain is due to the piriformis muscle compressing the sciatic nerve, such as while sitting on a car seat or running. Pain may also be triggered while climbing stairs, applying firm pressure directly over the piriformis muscle, or sitting for long periods of time.
The exact causes of piriformis syndrome are unknown. Suspected causes include:
- Muscle spasm in the piriformis muscle, either because of irritation in the piriformis muscle itself, or irritation of a nearby structure such as the sacroiliac joint or hip
- Tightening of the muscle, in response to injury or spasm
- Swelling of the piriformis muscle, due to injury or spasm
- Bleeding in the area of the piriformis muscle
Any one or combination of the above problems can affect the piriformis muscle (causing buttock pain) and may affect the adjacent sciatic nerve (causing pain, tingling, or numbness in the back of the thigh, calf, or foot).