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Piriformis Muscle Anatomy

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Origin
  • Anterior surface of the sacrum (around the level of S2 to S4)
  • Gluteal surface of the ilium
  • Sacrotuberous ligament
Insertion
  • Greater trochanter of the femur (medial side of the superior aspect)
Action
  • Laterally rotates the thigh at the hip joint
  • Abducts the thigh at the hip joint (when the hip is flexed past 60°)
  • Stabilizes the head of the femur in the acetabulum
Innervation
  • Superior gluteal nerve
  • Ventral rami of S1 and S2
Blood Supply
  • Branches of the superior and inferior gluteal arteries
  • Internal pudendal artery
Last updated: Estimated Reading Time: 7 min

Location & Overview

The piriformis muscle is situated in the gluteal region and proximal thigh, with a flattened, pear-shaped appearance. It is positioned parallel to the posterior edge of the gluteus medius and lies deep to the gluteus maximus. The name “piriformis” is derived from the Latin words “pirum” and “forma,” which mean “pear” and “shape,” respectively. Piriformis syndrome is a common condition associated with this muscle, and typical symptoms include hip pain, buttock pain, and pain that radiates down the back of the leg. These symptoms may include shooting, burning, or aching sensations, as well as numbness and tingling.[1,2]

The piriformis muscle is part of a group of six short muscles that externally rotate the hip joint in the gluteal region. The other five muscles in this group are the obturator internus, quadratus femoris, obturator externus, superior gemellus, and inferior gemellus. The piriformis muscle’s tendon merges with the tendons of the inferior gemellus and superior gemellus, along with the obturator internus muscle, to form the conjoint tendon. This tendon then inserts onto the femur.[3]

Piriformis muscle from a posterior view.
Here, we can see the piriformis muscle from a posterior view.
Piriformis muscle posterolateral view
Here, we can see the piriformis muscle from a posterolateral view.
Piriformis muscle lateral view
Here, we can see the piriformis muscle from a lateral view.
Piriformis muscle from an anterior view.
Pictured here, we can see the piriformis muscle from an anterior view, with the segments of the sacrum labeled. As shown in the image, it is located between S2 and S4.
Piriformis muscle's location among the other muscles of the hip
Here, we can see the piriformis muscle highlighted in red among the other muscles in the area. Superficial muscles such as the gluteus maximus and gluteus medius have been removed so that we can see the piriformis.
Deep six hip external/lateral rotators
Pictured here are the deep six hip external rotator muscles: the piriformis, gemellus superior, gemellus inferior, obturator internus, obturator externus, and quadratus femoris. These muscles play an important role in stabilizing the hip joint and facilitating hip lateral rotation.

Origin & Insertion

The piriformis muscle originates from various regions, including the anterior surface of the sacrum between levels S2 and S4, the capsule of the adjacent sacroiliac joint, the gluteal surface of the ilium near the margin of the greater sciatic notch, and occasionally the sacrotuberous ligament. Its insertion point is located on the medial side of the superior aspect of the greater trochanter of the femur.[1]

An image of the piriformis origin marked in red on the anterior surface of the sacrum (between S2 and S4)
Pictured here is the main origin of the piriformis muscle on the anterior surface of the sacrum (between S2 and S4).
An image of the piriformis origin marked in red on the gluteal surface of the ilium
Pictured here is another origin of the piriformis on the gluteal surface of the ilium (near the posterior inferior iliac spine).
An image of the piriformis origin marked in red on the sacrotuberous ligament
Pictured here is the sacrotuberous ligament, which is another origin of the piriformis muscle. The piriformis would connect to the superior portion of this ligament.
An image of the piriformis insertion marked in red on the greater trochanter of the femur
Pictured here is the insertion of the piriformis muscle, which is located on the greater trochanter of the femur (on the medial side of its superior aspect).

Action & Function

The piriformis muscle is a lateral rotator of the hip; this action is also known as external rotation. The quadratus femoris, inferior gemellus, obturator internus, and obturator externus can also assist in this movement. When the hip is extended, the piriformis is in the most advantageous position to assist in lateral rotation of the femur. When the hip joint is flexed past around 60° of hip flexion, the piriformis muscle is in a more advantageous position for hip abduction.[1,4,5]

Variations in the body, tendon, and tendon insertion of the piriformis muscle can impact its actions. Although it has been suggested that the piriformis muscle functions as an internal rotator of the hip joint, this ability is dependent on an individual’s unique anatomical structure. Therefore, controversy exists regarding the precise actions of the piriformis muscle. The truth is that the piriformis muscle’s role as an internal rotator varies depending on the individual’s anatomy and where the muscle inserts. In most cases, the piriformis has a variation that makes it unsuitable for aiding in internal rotation of the hip joint.[6,1,7]

Image of a person demonstrating the movement of hip abduction.
This image shows an example of hip abduction, which involves moving the leg out to the side (laterally). The opposite of hip abduction is hip adduction. The piriformis muscle is an abductor of the hip joint when the hip is flexed past 60 degrees. Hip flexion involves lifting the leg up in front of you (toward the anterior of the body). Put simply, the piriformis can assist in hip abduction once the leg is lifted forward and the hip joint reaches 60 degrees of flexion.
Image of a person demonstrating the movement of external rotation.
This image depicts an example of hip external rotation, which involves rotating the leg from the hip joint outward (laterally). External rotation is also referred to as lateral rotation. The opposite of external rotation (lateral rotation) is internal rotation (medial rotation). The piriformis muscle is an external rotator of the hip joint.
Remember that the piriformis also stabilizes the head of the femur in the acetabulum (an action not shown in the images above).

Innervation

Previously, the piriformis muscle was said to be innervated by the ‘nerve to piriformis’. However, recent cadaveric research states: “a single ‘nerve to piriformis’ does not exist in the majority of specimens thus this term should be abandoned”.[8] Instead, the piriformis is most commonly innervated by the superior gluteal nerve and the ventral rami of S1 and S2.[1,8,9]

superior gluteal nerve
Pictured here, you can see the superior gluteal nerve. Branches of the inferior part of this nerve extend to innervate the piriformis muscle. Moreover, the piriformis receives direct innervation from the ventral rami of the S1 and S2 spinal nerves.

Blood Supply

The piriformis is supplied by branches of the superior gluteal, inferior gluteal, and internal pudendal arteries, which arise from the internal iliac arterial system.[10,11]

References

  1. [1] Chang C, Jeno SH, Varacallo M. Anatomy, Bony Pelvis and Lower Limb, Piriformis Muscle. (Updated 2021 Oct 11). In: StatPearls (Internet). Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519497/
  2. [2] Hicks BL, Lam JC, Varacallo M. Piriformis Syndrome. (Updated 2022 Feb 12). In: StatPearls (Internet). Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK448172/
  3. [3] Lezak B, Massel DH. Anatomy, Bony Pelvis and Lower Limb, Gemelli Muscles. 2021 Sep 7. In: StatPearls (Internet). Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 32491352.
  4. [4] Demirel A, Baykara M, Koca TT, Berk E. Ultrasound elastography findings in piriformis muscle syndrome. Indian J Radiol Imaging. 2018 Oct-Dec;28(4):412-418. doi: 10.4103/ijri.IJRI_133_18. PMID: 30662201; PMCID: PMC6319104.
  5. [5] Lung K, Lui F. Anatomy, Abdomen and Pelvis, Superior Gluteal Nerve. 2021 Aug 11. In: StatPearls (Internet). Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 30571029.
  6. [6] Windisch G, Braun EM, Anderhuber F. Piriformis muscle: clinical anatomy and consideration of the piriformis syndrome. Surg Radiol Anat. 2007 Feb;29(1):37-45. doi: 10.1007/s00276-006-0169-x. Epub 2007 Jan 10. PMID: 17216293.
  7. [7] Benzon HT, Katz JA, Benzon HA, Iqbal MS. Piriformis syndrome: anatomic considerations, a new injection technique, and a review of the literature. Anesthesiology. 2003 Jun;98(6):1442-8. doi: 10.1097/00000542-200306000-00022. PMID: 12766656.
  8. [8] Iwanaga J, Eid S, Simonds E, Schumacher M, Loukas M, Tubbs RS. The majority of piriformis muscles are innervated by the superior gluteal nerve. Clin Anat. 2019 Mar;32(2):282-286. doi: 10.1002/ca.23311. Epub 2018 Dec 21. PMID: 30408241.
  9. [9] Fishman LM, Hosseini M. Piriformis syndrome – a diagnosis comes into its own. Muscle Nerve. 2019 Apr;59(4):395-396. doi: 10.1002/mus.26417. Epub 2019 Feb 4. PMID: 30623985.
  10. [10] Goidescu OC, Enyedi M, Tulin AD, et al. Overview of the anatomical basis of the piriformis syndrome-dissection with magnetic resonance correlation. Exp Ther Med. 2022;23(2):113. doi:10.3892/etm.2021.11036
  11. [11] Chang C, Jeno SH, Varacallo M. Anatomy, Bony Pelvis and Lower Limb, Piriformis Muscle. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2023.

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