Lower limb

Piriformis

Musculus piriformis

Origin

Anterior (pelvic) surface of the sacrum, at the level of S2-S4

Insertion

Superior border of the greater trochanter of the femur

Function

External rotation of the hip in extension; abduction of the hip in flexion; stabilizes the femoral head

Innervation

Nerve to piriformis (sacral plexus, S1-S2)

Movement & chain

Part of the deep external rotator group of the hip together with the obturators, gemelli and quadratus femoris; also active in pelvic stabilization during single-leg stance.

Palpation

Difficult to palpate directly due to the overlying gluteus maximus, but deep pressure midway between the sacrum and the greater trochanter can reproduce piriformis syndrome pain.

Clinical

The sciatic nerve runs just beneath (sometimes through) this muscle; spasm or hypertrophy can cause piriformis syndrome, with pain radiating along the course of the sciatic nerve.

Segmental innervation

S1-S2.

In clinical practice

Important landmark in the differential diagnosis of radiating buttock pain and for injections near the sciatic nerve.

Region in the model

Lower limb