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Piriformis Muscle

Contents

Introduction

Piriformis is a muscle of the gluteal region which lies deep to the visible muscle, i.e. 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. 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. 

Recommended video: Muscles of the Hip and Thigh
Overview of the muscles found on the hip and the thigh.

Attachments and course

Piriformis muscle - superior view

Piriformis muscle - superior view

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. It inserts onto 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.

Piriformis muscle - dorsal view

Piriformis muscle - dorsal view

Action

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 outward rotation of the hip joint, together with abduction of the thigh.

Innervation

The nerve supply to piriformis is from a specific nerve of the lumbosacral plexus (nerve to piriformis, L5-S2).

Blood supply

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

Clinical Points

Piriformis syndrome

This is a syndrome that occurs when the sciatic nerve is compressed or irritated (i.e. a sciatica) by the piriformis muscle. This condition is more likely to occur in individuals with anatomical variations of the sciatic nerve and piriformis. Other causes of sciatica include a herniated disc between L5 and S1. This can be diagnosed by a MRI scan, and treated with surgery. The symptoms of piriformis syndrome include:

  • buttock pain
  • tenderness over the greater sciatic notch
  • worsening of pain during sitting and when performing movements which increase tension in the piriformis muscle (Flexion/Adduction/Internal Rotation of the hip, i.e. FAIR test).

Variant anatomy

There is variation in the location of the insertion footprint of piriformis on the greater trochanter of the femur. The relationship between piriformis and the sciatic nerve can also vary. In the vast majority of individuals, the sciatic nerve leaves the bony pelvis via the greater sciatic foramen, below piriformis and divides into tibial nerve and common peroneal nerve distally to piriformis. In some people, the nerve divides proximally. Examples of variations include a bifid sciatic nerve passing inferior to a hypertrophied piriformis, or a common peroneal nerve passing between the two bellies of a bifid piriformis, the tibial nerve passing inferior to piriformis. Both the tibial and common peroneal nerves can also pass through or superior to piriformis.

Total hip replacement 

In minimally invasive total hip arthroplasty, such as the direct anterior approach, the hip joint is surgically approached in a way which minimises soft tissue dissection. This method improves the postoperative stability of the joint and reduces the risk of dislocation. However during the detachment of the joint capsule, the short external rotators of the hip, including piriformis, are at risk of damage.

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Show references

References:

  • Frank H.Netter MD: Atlas of Human Anatomy, 5th Edition, Elsevier Saunders.
  • Chummy S.Sinnatamby: Last’s Anatomy Regional and Applied, 12th Edition, Churchill Livingstone Elsevier.
  • Richard L. Drake, A. Wayne Vogl, Adam. W.M. Mitchell: Gray’s Anatomy for Students, 2nd Edition, Churchill Livingstone Elsevier.
  • Jeremy J. MD: Piriformis. Radiopaedia.org (accessed 15/02/2016).
  • Dissector Answers - Pelvic Neurovasculature. The University of Michigan (accessed 15/02/2016).
  • Swenson R. DC, MD, PhD: The gluteal region. O'Rahilly 2008 (accessed 15/02/2016).

Author, Review and Layout:

  • Shahab Shahid
  • Jérôme Goffin
  • Catarina Chaves

Illustrators:

  • Piriformis muscle - superior view - Liene Znotina
  • Piriformis muscle - dorsal view - Liene Znotina
© Unless stated otherwise, all content, including illustrations are exclusive property of Kenhub GmbH, and are protected by German and international copyright laws. All rights reserved.

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