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Piriformis Muscle

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Description

  • Anatomy of the piriformis muscle. (A) Anatomic illustration shows the location and course of the piriformis muscle (red area). (B) 3-T axial T1-weighted MR image shows the left and right piriformis muscle (white arrows) and the proximal neurovascular bundles (circles) containing the sciatic nerve.[1]
    Anatomy of the piriformis muscle. (A) Anatomic illustration shows the location and course of the piriformis muscle (red area). (B) 3-T axial T1-weighted MR image shows the left and right piriformis muscle (white arrows) and the proximal neurovascular bundles (circles) containing the sciatic nerve.[1]
  • Schematic location of the sciatic nerve travelling below the piriformis muscle.[2]
    Schematic location of the sciatic nerve travelling below the piriformis muscle.[2]
  • Illustration of displaying the release of the piriformis muscle. On the left side of the image, the sciatic nerve is displayed in its typical location below the piriformis muscle. On the right side of the image, the sciatic nerve is shown decompressed after cutting of the piriformis muscle[3]
    Illustration of displaying the release of the piriformis muscle. On the left side of the image, the sciatic nerve is displayed in its typical location below the piriformis muscle. On the right side of the image, the sciatic nerve is shown decompressed after cutting of the piriformis muscle[3]
  • Anatomic variations of the relationship between the piriformis muscle and sciatic nerve. (a) An undivided nerve emerges below the piriformis muscle (normal course)[4]
    Anatomic variations of the relationship between the piriformis muscle and sciatic nerve. (a) An undivided nerve emerges below the piriformis muscle (normal course)[4]
  • Diagram of the piriformis muscle ’ s surface marking. GT greater trochanter, PSIS posterior superior iliac spine, X point midway between coccyx and PSIS[5]
    Diagram of the piriformis muscle ’ s surface marking. GT greater trochanter, PSIS posterior superior iliac spine, X point midway between coccyx and PSIS[5]
Illustration of the piriformis anatomy
Beaton and Anson classification of different anatomical relationships between the sciatic nerve and piriformis muscle and their estimated prevalence. (a) Type 1: undivided sciatic nerve passing anterior and below the piriformis. (b) Type 2: common peroneal nerve component piercing a bifid piriformis, tibial component running in normal position anterior and inferior to piriformis. (c) Type 3: one division posterior to and the other anterior to the piriformis. (d) Type 4: undivided sciatic nerve piercing bifid piriformis. (e) Type 5: one division through and the other posterior to the piriformis. (f) Type 6: undivided nerve posterior to piriformis.[6]
The normal anatomy of the sciatic nerve in relationship to the piriformis muscle[7]

Name

  • Piriformis Muscle
  • Piriformis
  • Musculus piriformis (Latin)
  • Piriformis gluteal muscle
  • Deep gluteal muscle
  • Sciatic notch muscle

Etymology

  • The term "piriformis" is derived from the Latin words pirum (pear) and forma (shape)

Origin

Insertion

Actions

  • External rotation of hip when in extension
  • Abduction of hip when in flexion
  • Stabilizes Femur in acetabulum

Vascular supply

  • Superior Gluteal Artery
  • Inferior Gluteal Artery
  • Internal Pudendal Artery (gemellar branches)

Innervation

Anatomic relationship to Sciatic Nerve

  • Beaton et al cadaveric study[8]
    • 90% of cadavers had traditional anatomy with an undivided sciatic nerve emerging below the piriformis muscle
    • Divided sciatic nerve passing through and below the piriformis muscle
    • Divided sciatic nerve passing above and below the piriformis muscle
    • Undivided nerve passing through the piriformis muscle
  • Smoll et al systematic review and meta-analysis[9]
    • 16.9% of cadavers: abnormal relationship between the sciatic nerve and piriformis muscle
  • Bartet et al MRI study[10]
    • 19.2% of MRI revealed an abnormal relationship between the sciatic nerve and piriformis muscle
  • Beason and Anson Classification[11]
    • Type A. Undivided nerve below a undivided muscle
    • Type B. Division of the nerve between and below an undivided muscle
    • Type C. Division of the nerve below and above an undivided muscle
    • Type D. Undivided nerve between heads
    • Type E. Division between and below divided heads
    • Type F. Undivided nerve above an undivided muscle
  • Conventional anatomic classification
    • Type 1: sciatic nerve passes below the PM (observed in 87%)
    • Type 2: one division passes through the PM and another below it (observed in 13%)
    • Type 3: sciatic nerve exits above the PM (noted rarely)

Clinical Significance

Pathology

Procedure

See Also

References

  1. ↑ Fritz, Jan, et al. "Magnetic resonance Neurography–Guided nerve blocks for the diagnosis and treatment of chronic pelvic pain syndrome." Neuroimaging Clinics 24.1 (2014): 211-234.
  2. ↑ Fahmi, Achmad, et al. "Complete resolution of recurrent piriformis syndrome after piriformis resection with 3 years’ follow up: A case report." International Journal of Surgery Case Reports 77 (2020): 576-579.
  3. ↑ Hogan, Elizabeth, Darshan Vora, and Jonathan H. Sherman. "A minimally invasive surgical approach for the treatment of piriformis syndrome: a case series." Chinese Neurosurgical Journal 6.1 (2020): 8.
  4. ↑ Capurro, Bruno, et al. "Hitos Anatómicos para un Abordaje Artroscópico Seguro del Espacio Glúteo Profundo: Un Estudio Cadavérico." International Journal of Morphology 39.2 (2021): 359-365.
  5. ↑ Ismail, Hossam El-din Ali. "Versatility of perforator sparing buttock rotation flap in repair of pressure sores." European Journal of Plastic Surgery 35.1 (2012): 89-95.
  6. ↑ Bharadwaj, Upasana Upadhyay, et al. "Variant Sciatic Nerve Anatomy in Relation to the Piriformis Muscle on Magnetic Resonance Neurography: A Potential Etiology for Extraspinal Sciatica." Tomography 9.2 (2023): 475-484.
  7. ↑ Meknas, Khaled, Oddmund Johansen, and Jüri Kartus. "Retro-trochanteric sciatica-like pain: current concept." Knee Surgery, Sports Traumatology, Arthroscopy 19.11 (2011): 1971-1985.
  8. ↑ Beaton LA, Anson BJ. The sciatic nerve and the piriformis muscle: their interrelation a possible cause of coccygodynia. J Bone Joint Surg. 1938;20(3):686‐688.
  9. ↑ Smoll NR. Variations of the piriformis and sciatic nerve with clinical consequence: a review. Clin Anat. 2010;23(1):8‐17.
  10. ↑ Bartret AL, Beaulieu CF, Lutz AM. Is it painful to be different? Sciatic nerve anatomical variants on MRI and their relationship to piriformis syndrome. Eur Radiol. 2018;28(11):4681‐4686.
  11. ↑ Beaton, Lindsay E., and Barry J. Anson. "The relation of the sciatic nerve and of its subdivisions to the piriformis muscle." The Anatomical Record 70.1 (1937): 1-5.
Created by:
Chris Hauglid on 7 July 2020 18:28:55
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Last edited:
12 December 2025 02:35:23
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