Piriformis

Original Editor - Lucas Villalta

Top Contributors - Lucas Villalta, Vidya Acharya, Kim Jackson, Candace Goh, 127.0.0.1, Laura Ritchie, Evan Thomas, WikiSysop and Wendy Snyders;

Description

The piriformis is a thick, flat muscle and the most superficial muscle among the deep gluteal muscles. It is part of the lateral rotators of the hip (obturator internus, superior and inferior gemelli, quadratus femoris, obturator externus, and gluteus maximus). The muscle leaves the pelvis through the greater sciatic notch until it attaches to the superior margin of the greater trochanter. Shaped like a pear, it lies nearly parallel to the posterior margin of the gluteus medius.

Anatomy

Origin

• Anterior aspect of the sacrum at the level of about S2 through S4
• Sacrotuberous ligament
• Periphery of the greater sciatic notch

Insertion

• Superior and medial aspects of the greater trochanter.

Nerve

• Anterior Rami of S1 and S2

Artery

• The arterial supply is from the inferior gluteal, superior gluteal and internal pudendal arteries, all branches of the internal iliac artery.

Function

• Lateral rotation of the hip when it is extended (e.g. standing).
• Abduction of the hip when it is flexed.
• Aids slightly in tilting pelvis laterally.
• Also aids in tilting pelvis posteriorly by pulling the sacrum down towards the thigh.

Clinical relevance

The piriformis muscle can be used to locate the sciatic nerve. The sciatic nerve enters the gluteal region inferiorly to the piriformis. If the lateral rotators of the hip are tight, they may exert pressure on the sciatic nerve, producing pain radiating into the lower extremity. This is known as Piriformis Syndrome.

Piriformis also divides the gluteal region into a superior and inferior part. Therefore, it determines the name of the vessels and nerves that supply the area (e.g. the superior gluteal nerve and vessels emerge superiorly to the piriformis, and the inferior gluteal nerve and vessels emerge inferiorly to the piriformis).

Assessment

Palpation

It may be palpable indirectly through the gluteus maximus into the greater sciatic notch.

Test

Piriformis Test