The piriformis muscle originates on the anterior surface of the sacrum and it is securely held to it by three tissue attachments found between the first, second, third and fourth anterior sacral foramina. Occasionally, its origin may be so broad that it joins the capsule of the sacroiliac joint with the sacrotuberous and/or sacrospinous ligament. The piriformis muscle is a thick and strong muscle that travels out of the pelvis through the greater sciatic foramen, dividing the foramen into the suprapiriform and infra-piriform foramina. As it courses through the greater sciatic foramen, the muscle decreases to a point where it forms a tendon that attaches to the superior-medial surface of the greater trochanter, frequently integrating with the tendon of the obturator internus and gemelli muscles.

The nerves and blood vessels found within the suprapiriform foramen are known as the superior gluteal nerves and vessels, and those found in the infra-piriforma fossa are known as the inferior gluteal nerves and vessels, including the sciatic nerve. Because of its broad size in the greater sciatic foramen, there’s a risk the numerous vessels and nerves that exit the pelvis may become compressed.

The piriformis muscle is closely associated with other short hip rotators as well, such as the superior gemellus, obturator internus, inferior gemellus and obturator externus. The primary difference between this muscle and other short rotators is its connection to the sciatic nerve. The piriformis muscle passes behind the nerve while the other rotators pass before it.