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Piriformis muscle: want to learn more about it?

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Piriformis muscle

Piriformis is a muscle of the gluteal region which lies deep to the gluteus maximus. Piriformis belongs to a group of six short external rotators of the hip , i.e. gemellus superior, obturator internus, gemellus inferior, quadratus femoris, obturator externus. Attaching to the sacrum on one end and the greater trochanter on the other one, this muscle is reponsible for stabilizing the hip joint and moving the thigh in various directions.

In this article we will discuss the anatomy of piriformis, as well as its neurovascular supply and function. In addition we discuss the clinical relevance of the muscle.

Key facts about the piriformis muscle
Origin Anterior surface of the sacrum (between the S2 and S4), Gluteal surface of ilium (near posterior inferior iliac spine), (Sacrotuberous ligament)
Insertion (Apex of) Greater trochanter of the femur
Action Hip joint: Thigh external rotation, Thigh abduction (from flexed hip); Stabilises head of femur in acetabulum
Innervation Nerve to piriformis (S1-S2)
Blood supply Superior gluteal artery, inferior gluteal artery, gemellar branches of the internal pudendal
Mnemonic Structures passing through the greater sciatic foramen inferior to piriformis muscle: PIN PINS
(standing for: Posterior cutaneous nerve of thigh, Inferior gluteal vessels and nerves, Nerve to quadratus femoris, Pudendal nerve, Internal pudendal vessels, Nerve to obturator internus, Sciatic nerve)

Origin and insertion

This is a flat pyramid-shaped muscle that arises from the anterior surface of the sacrum, between the sacral foramina. It passes laterally to exit the bony pelvis through the greater sciatic foramen, often attaching to the gluteal surface of the ilium, close to the posterior inferior iliac spine. It inserts onto the apex of the greater trochanter, posterosuperior to the insertion site of the conjoined tendon of gemellus superior, obturator internus and gemellus inferior.

The muscle divides the greater sciatic foramen into two foramina (suprapiriform and infrapiriform). The superior gluteal artery and nerve (L4-S1) leave the pelvis through the suprapiriform foramen. The sciatic nerve, inferior gluteal nerve (L5-S2) and artery, posterior femoral cutaneous nerve (S1-S3) and the nerve to quadratus femoris (L4-S1) leave the pelvis through the infrapiriform foramen. The pudendal nerve (S2-4) also leaves the pelvis through the infrapiriform foramen, wraps around the sacrospinous ligament, and re-enters the pelvis by passing back into the lesser sciatic foramen. After re-entering the pelvis, it is joined by the internal pudendal artery and vein. The gluteus medius and minimus are medial rotators, and hence oppose the action of the lateral rotators.

Want a super easy way to learn the actions, attachments and functions of the Piriformis muscle? You need our lower extremity muscle anatomy chart. 

The structures that leave the pelvis through the infrapiriform foramen can be easily remembered with the following mnemonic; 

PINS & PINS

  • Posterior cutaneous nerve of thigh
  • Inferior gluteal vessels and nerves
  • Nerve to quadratus femoris
  • Pudendal nerve
  • Internal pudendal vessels
  • Nerve to obturator internus
  • Sciatic nerve

If you want to learn the anatomy of the hip muscles, including piriformis, in a more visual way, take a look at the videos, illustrations and quizzes in the following study unit:

Innervation

The nerve supply to piriformis comes from the nerve to piriformis, formed from the anterior rami of S1 and S2 spinal nerves.

Blood supply

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

Functions

In combination with the other posterior hip muscles, the piriformis stabilizes the hip joint by steadying the head of the femur inside the acetabulum of the hip bone. It also contributes to the retroversion and external rotation of the hip joint, in addition to abduction of the thigh while in the flexed position.

Piriformis muscle: want to learn more about it?

Our engaging videos, interactive quizzes, in-depth articles and HD atlas are here to get you top results faster.

What do you prefer to learn with?

“I would honestly say that Kenhub cut my study time in half.” – Read more. Kim Bengochea Kim Bengochea, Regis University, Denver

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