Piriformis

The piriformis (from Latin piriformis = "pear shaped") is a muscle in the gluteal region of the lower limb. It runs from the base of the spine to the top of the femur, or thigh bone. Its action is to rotate the thigh laterally (outward).

More precisely, it originates from the anterior (front) part of the sacrum, the part of the spine in the gluteal region, and from the gluteal surface of the ilium (as well as the sacro-iliac joint capsule and the sacrotuberous ligament). It inserts on the greater trochanter of the femur. Its tendon often joins with the tendons of the superior gemellus, inferior gemellus, and obturator internus muscles prior to insertion.

The piriformis muscle is innervated by L5, S1, and S2 nerve roots.

The piriformis is often affected or indentified as the root of pain in sciatica.