piriformis

The piriformis is a small, flat, pear-shaped muscle of the gluteal region. It originates from the anterior (pelvic) surface of the sacrum and the sacrotuberous ligament, and it exits the pelvis through the greater sciatic foramen to insert on the superior border of the greater trochanter of the femur. Its course places it in close relationship to the sciatic nerve and other gluteal structures.

The muscle is innervated by the nerve to the piriformis, a branch of the sacral plexus derived from ventral rami S1 and S2. Its blood supply comes from branches of the superior and inferior gluteal arteries, with variations in local vascular anatomy.

Functionally, the piriformis acts as a lateral rotator of the thigh when the hip is extended and as an abductor when the hip is flexed. It also helps stabilize the hip joint and assists in pelvic rotation during gait. The tendon blends with surrounding deep gluteal muscles, contributing to the region’s overall rotatory and stabilizing mechanics.

Clinically, the piriformis is notable for piriformis syndrome, a condition in which spasm, hypertrophy, or fibrosis of the muscle irritates or compresses the nearby sciatic nerve, causing buttock pain and radiating symptoms similar to sciatica. Diagnosis is clinical, supported by imaging or provocative maneuvers, and management typically includes physical therapy, targeted stretching, and, in some cases, injections or surgical release if conservative treatment fails.

Anatomical variations exist in the relationship between the piriformis and the sciatic nerve; in some individuals, the sciatic nerve or its divisions may pass through or above the muscle, which can influence symptomatology and treatment considerations.