The piriformis muscle (the pelvis surface of the sacrum from the 2nd to 4th segments lateral to the anterior foramina to the top of the greater trochanter, the muscle passing out of the pelvis through the greater sciatic foramen) fills the greater sciatic foramen. When shortened, the muscle can sometimes compress the sciatic nerve and cause pain in its distribution.
The “piriformis syndrome” is suspected when there is point tenderness in the sciatic notch, as well as during rectal examination. Rarely, the muscle can also become tender, and is the site of pain in sacroiliitis. The muscle can be palpated and needled through the gluteus maximus after the latter is relaxed.