Piriformis Syndrome: A Pain in the Butt

Article Outline

• Anatomy and Etiology
• Clinical Presentation
• Differential Diagnoses
• Diagnostic Imaging
• References
• Copyright

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Piriformis syndrome (PS) is often not considered in the differential diagnosis of sciatica, yet the incidence varies from 5% to 36% of low back pain patients, affecting more women than men.¹ It is important that nurse practitioners (NPs) recognize signs and symptoms of PS in comparison to other conditions presenting with sciatica.

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Anatomy and Etiology 

The piriformis muscle lies deep in the buttock. It originates at the anterior sacrum, travels laterally through the greater sciatic notch, and inserts on the greater trochanter. The piriformis functions as an external hip rotator when standing and hip abductor and flexor when sitting. The sciatic nerve usually runs underneath, but through it in up to 22% of the population. This close relationship of the sciatic nerve and piriformis muscle leads to PS symptoms when muscle spasm compresses the nerve. Frequent PS causes are buttock trauma (falls, sports injury), compression (prolonged sitting) and overuse (runners, skiers).¹

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Clinical Presentation 

Patients with PS report deep buttock pain aggravated by sitting. They point to the specific spot of maximal pain over the piriformis muscle and its attachment sites. Pain and sensory changes may radiate down the posterior thigh because the muscle is innervated by L5, S1, and S2 branches. Straight-leg-raising (SLR) tests are negative because there is no disk herniation. Piriformis muscle palpation is painful and often reveals muscle spasm. The FAIR test (flexion, adduction, and internal rotation) maximally elongates the piriformis muscle to recreate sciatic symptoms with a sensitivity of 0.881 and specificity of 0.832.² To perform the FAIR test, the patient lies on the unaffected side, knees bent 60° to 90° and hip flexed 60°. Stabilize the involved hip while internally rotating and adducting it. Hook the foot of the involved leg behind the calf of the unaffected leg and apply downward pressure on the top knee until it touches the table. Other findings may include pain and weakness with resisted abduction/external rotation while sitting (positive Pace test), and pain with internal hip rotation (positive Freiberg test).¹

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Differential Diagnoses 

Clinical presentation of the 4 most frequent and 2 rare but ominous differential diagnoses for sciatica are noted in Table 1. The NP must do a thorough history and focused physical assessment of the patient to rule out other causes of sciatica, because PS is primarily a diagnosis of exclusion that is based on clinical presentation. Physical examination should focus on pain location, inspection, range of motion, spine and muscle palpation, strength, sensation, and reflexes in both legs. For patients with leg symptoms, ipsilateral and contralateral SLR tests, and motor and sensory evaluation of L5 and S1 roots should be conducted. Assess peripheral pulses. If findings suggest a systemic cause, evaluate with appropriate tests for malignancy (lung, breast, pelvic, prostate, and lymph nodes), and obtain an erythrocyte sedimentation rate.

Table 1. Conditions Commonly Presenting With Sciatica

Indications for urgent imaging and referral: Cauda equina syndrome, suspicion of spinal cord compression, epidural abscess, severe or progressive neurologic deficits. SLR indicates straight-leg-raise test; ROM, range of motion; FAIR, flexion, adduction, and internal rotation; IVDU, intravenous drug use.

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Diagnostic Imaging 

Imaging studies are not necessary in the first 4 to 6 weeks for most patients with low back pain. Exceptions to this are if malignancy or infection, a compression fracture, trauma, or major neurological deficits are suspected. Risks for or history of cancer, unexplained weight loss, age over 50 years, and nighttime pain are clues to malignancy as a cause. Fevers, intravenous drug use, indwelling catheters, and urinary tract or skin infections raise concerns for vertebral osteomyelitis or epidural abscess. Saddle anesthesia, bowel or bladder dysfunction, bilateral sciatica, and leg weakness strongly suggest cauda equina syndrome, a medical emergency most commonly caused by a tumor or massive herniation. Magnetic resonance imaging is indicated to detect tumors, spinal cord compression, cauda equina syndrome, epidural abscess, osteomyelitis, and herniated disk. Computed tomography scans are useful to detect spinal stenosis and arthritic changes.³ Diagnostic imaging is not helpful in diagnosing PS, although magnetic resonance neurography shows promise.⁴

By using the information in Table 1 as a guide, NPs can distinguish PS in the differential diagnosis of low back with sciatica in primary care.

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References 

1. Boyajian-O'Neill LA , McClain RL , Coleman MK , Thomas PP . Diagnosis and management of piriformis syndrome: an osteopathic approach . J Am Osteopath Assoc . 2008;108(11):657–664
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2. Fishman LM , Dombi GW , Michaelsen C , Ringel S , Rozbruch J , Rosner B , et al.   Piriformis syndrome: diagnosis, treatment, and outcome—a 10-year study . Arch Phys Med Rehabil . 2002;83:295–301
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3. Goroll AH , Mulley AG . In: Primary care medicine: office evaluation and management of the adult patient . 5th ed.. Philadelphia, PA: Lippincott Williams & Wilkins; 2006;p. 955–970
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4. Filler AG . Piriformis and related entrapment syndromes: diagnosis and management . Neurosurg Clin North Am . 2008;19(4):609–622
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