Piriformis muscle

The piriformis muscle is a deep skeletal muscle connecting the anterior sacrum to the upper femur. It passes through the greater sciatic foramen and helps rotate the extended thigh outward and abduct the flexed thigh. Its position makes it a useful landmark: the sciatic nerve usually emerges below it, although the relationship varies between people.^[ref]

An anatomical variant alone does not establish a cause of pain. Adam L. Bartret and colleagues classified sciatic nerve routes on 783 hip magnetic resonance imaging examinations; variants occurred in about 19%, without a statistically significant association with a recorded diagnosis of piriformis syndrome. This observation separates a visible anatomical difference from evidence that the difference explains symptoms.^[ref]