Nerve to piriformis muscle

At a glance

English

Nerve to piriformis muscle

Latin (TA2)

Nervus musculi piriformis

System

Nerve

Region

Lower limb

Side

Paired, left and right

About the nerve to piriformis muscle

Piriformis arises inside the pelvis from the front of the sacrum and passes out through the greater sciatic foramen to the top of the greater trochanter of the femur. Its nerve stays within the pelvis. It arises from the posterior divisions of the anterior rami of the first and second sacral nerves, sometimes from the second alone, and enters the front, pelvic surface of the muscle directly.

The sacral plexus itself lies on the front of piriformis, covered by the parietal pelvic fascia, with the internal iliac vessels and the ureter in front of it. The nerve to piriformis is therefore one of the shortest branches of the plexus, passing straight back into the muscle on which the plexus rests. Most other branches of the plexus, including the sciatic, gluteal and posterior femoral cutaneous nerves, leave the pelvis through the greater sciatic foramen.

Piriformis rotates the extended thigh outwards and helps abduct the thigh when the hip is bent; it also helps hold the head of the femur in the acetabulum. Its close relation to the sciatic nerve, which usually leaves the pelvis just below it but in some people passes through or above it, underlies piriformis syndrome, a disputed cause of buttock pain spreading down the back of the thigh.

Course and supply

Arises from

Posterior divisions of the anterior rami of S1 and S2 (sometimes S2 alone), in the sacral plexus.

Ends in

Anterior (pelvic) surface of piriformis.

Supplies

Motor supply to piriformis.