Piriformis Syndrome

General Information

Description:

  • Sciatica attributed to spasm of piriformis muscle


Also called:

  • Piriformis syndrome


Organs involved:

  • Piriformis is external rotator and abductor of thigh located deep to gluteus muscles
  • Piriform muscle arises from ilium and 2nd-4th sacral vertebrae and inserts at upper border of greater trochanter, innervated by S1-S2


Incidence/Prevalence:

  • Uncommon but may be underdiagnosed


Causes and Risk Factors

Causes:

  • Piriformis spasm or contracture
  • Local trauma to buttocks
  • Repeated mechanical stressors (running)
  • Sacral base unleveling, pelvic instability
  • Excessive local pressure especially in thin patients (“hip pocket neuritis”)
    • Case report of piriformis syndrome and sciatica attributed to external hip protector can be found in J Am Geriatr Soc 2005 Mar;53(3):553


Pathogenesis:

  • Sciatic nerve irritated by tight piriformis muscle
  • Existence of piriformis syndrome suggested by magnetic resonance neurography
    • In cohort of 239 patients with sciatica unresponsive to standard diagnosis and treatment
      • Final re-diagnosis was piriformis syndrome in 68% after magnetic resonance neurography and interventional MRI
      • Piriformis muscle asymmetry and sciatic nerve hypersensitivity at sciatic notch on magnetic resonance neurography had 64% sensitivity and 93% specificity for piriformis syndrome
      • Reference – J Neurosurg Spine 2005 Feb;2(2):99
    • In case series of 14 patients with sciatic distribution pain and normal lumbosacral MRI who had magnetic resonance neurography of lumbosacral plexus and sciatic nerves
      • 12 patients had increased signal in ipsilateral sciatic nerve, usually at sciatic notch at or just inferior to level of piriformis muscle
      • 4 patients had surgical decompression, of whom 3 had symptom relief
      • Reference – Arch Neurol 2006 Oct;63(10):1469


Complications and Associated Conditions

Complications:

  • Sciatica
  • Disability (Radiol Med (Torino) 2003 Jan-Feb;105(1-2):69)