Piriformis Syndrome

Pain in the buttock, with or without sciatic type referral down the leg, attributed to compression or irritation of the sciatic nerve by the piriformis muscle in the deep gluteal space. It is a form of deep gluteal syndrome.

• It is a controversial and probably overdiagnosed condition, accounting for about 0.3 to 6% of cases of low back pain and sciatica in clinical series, and is more common in women (about 6 to 1) and in the fourth and fifth decades.
• Causes:
  • Primary (anatomical variant): the sciatic nerve passes through or splits the piriformis muscle in about 10 to 15% of people, but only a few develop symptoms.
  • Secondary: trauma to the buttock (a fall onto the buttock, with haematoma and scarring), repetitive hip rotation and sitting on hard surfaces (cyclists, runners, rowers, drivers, wallet sitting), muscle hypertrophy or spasm, hip or sacroiliac pathology, leg length discrepancy, and post-surgical scarring.
  • Other deep gluteal space causes: ischiofemoral impingement, proximal hamstring tendon pathology, gemelli obturator internus entrapment, vascular lesions and masses.
• Risk factors: prolonged sitting, repetitive hip external rotation, trauma, and gluteal muscle imbalance.

• Deep, aching buttock pain, sometimes burning or electric, radiating to the posterior thigh and occasionally to the calf and foot, mimicking sciatica. Pain increases with prolonged sitting (the commonest feature), climbing stairs, squatting, hip flexion with adduction and internal rotation, running, and rising from a chair. Relief on standing or walking, or lying on the unaffected side. Coughing does not usually aggravate it.
• Neurological examination is usually normal, with possible mild sensory change in the sciatic distribution. Muscle weakness and reflex loss are uncommon and suggest an alternative cause.
• Examination: deep tenderness over the greater sciatic notch and piriformis (palpable tender cord on rectal or vaginal examination in some), pain on resisted abduction and external rotation of the hip in sitting, and positive provocative tests:
  • FAIR test: pain with passive flexion, adduction and internal rotation of the hip.
  • Pace sign: pain and weakness on resisted abduction and external rotation of the flexed hip while seated.
  • Freiberg sign: pain on passive internal rotation of the extended hip.
  • Beatty manoeuvre: pain on lifting the flexed knee of the affected leg toward the ceiling while lying on the unaffected side.
  • Seated piriformis stretch test and active piriformis test.
• Differential diagnosis: lumbar disc herniation with radiculopathy, lumbar spinal stenosis, facet joint syndrome, sacroiliac joint dysfunction, gluteal tendinopathy, proximal hamstring tendinopathy, ischiofemoral impingement, hip osteoarthritis and labral tear, lumbosacral plexopathy, pudendal neuralgia, ischial bursitis, coccydynia, tumour, vascular claudication (gluteal), endometriosis, and pelvic mass.
• Red flags: cauda equina features, progressive weakness, fever, weight loss, history of cancer, and severe night pain.
• Complications: chronic pain, sciatic nerve injury (rare), disability, and delayed diagnosis of other conditions.

• Clinical and largely a diagnosis of exclusion. Exclude lumbar radiculopathy first, with a lumbar spine MRI when sciatica is prominent.
• MRI of the pelvis or magnetic resonance neurography shows piriformis asymmetry or hypertrophy, sciatic nerve signal change or compression, and other deep gluteal lesions. Ultrasound can show muscle bulk and guide injection.
• Electrodiagnostic testing: the FAIR test with H-reflex delay (a prolongation of 1.86 ms or more of the peroneal or tibial H-reflex in the FAIR position) supports the diagnosis, though it is not widely available. Electromyography to exclude radiculopathy and plexopathy.
• Diagnostic injection of lidocaine into the piriformis muscle with relief of pain supports the diagnosis.
• Pelvic and rectal examination, and imaging when a mass or gynaecological cause is suspected.

• Conservative treatment (first line, most patients improve in 6 to 12 weeks):
  • Avoid aggravating activities (prolonged sitting, hip adduction, running on hills, wallet in the back pocket), use a cushion with a cut out, change position every 20 to 30 minutes, and sleep with a pillow between the knees.
  • Heat before stretching, ice after activity.
  • Analgesia: paracetamol 1 g orally 6 hourly. NSAIDs for 1 to 2 weeks (ibuprofen 400 mg 8 hourly with food, naproxen 500 mg 12 hourly, or diclofenac 50 mg 8 hourly). Topical diclofenac 1% gel. A muscle relaxant for 5 to 7 days (tizanidine 2 mg at night increasing to 2 to 4 mg 8 hourly, or cyclobenzaprine 5 to 10 mg at night). Neuropathic agents for persisting sciatic pain: gabapentin 300 mg at night increasing to 900 to 1800 mg daily in divided doses, or amitriptyline 10 to 25 mg at night.
  • Physiotherapy: piriformis and hip external rotator stretching (supine figure four stretch, seated cross leg stretch, held for 30 seconds, repeated 3 to 5 times, 2 to 3 times daily), strengthening of the gluteus maximus, medius and core, hip mobilisation, soft tissue release, and correction of gait and posture. Strengthening of the hip abductors and extensors should be emphasised, because stretching alone is often insufficient.
  • Dry needling and manual trigger point release provide short term benefit.
• Injection therapy for refractory pain after 6 to 8 weeks, with ultrasound, fluoroscopic or CT guidance for accurate needle placement (blind injections miss the muscle in a high proportion of cases):
  • Local anaesthetic with corticosteroid: lidocaine 1% 3 to 5 mL (or bupivacaine 0.25 to 0.5% 3 to 5 mL) with triamcinolone acetonide 40 mg (or methylprednisolone acetate 40 mg), injected into the belly of the piriformis. Relief lasts weeks to months. Risk: sciatic nerve injury or block (transient leg weakness, so warn about driving), infection, bleeding, and fat atrophy.
  • Botulinum toxin type A: 100 units (range 50 to 200 units) of onabotulinumtoxinA into the piriformis under guidance, with relief for 2 to 4 months in about 60 to 70% of patients in small studies. Use is specialist and off label, with evidence limited.
  • Prolotherapy and platelet rich plasma have limited evidence.
• Surgical treatment for failure after 6 months of conservative and injection treatment, or when an anatomical cause is found: endoscopic or open piriformis tendon release and sciatic nerve decompression, with resection of fibrous bands, or removal of an offending mass, with 60 to 80% improvement in selected patients. Rehabilitation takes 6 to 12 weeks.
• Special groups:
  • Pregnancy: positioning, stretching and physiotherapy, and paracetamol. Avoid NSAIDs after 20 weeks, and avoid injection with steroid unless essential.
  • Athletes (runners, cyclists, rowers): correct technique, bike fit, training load, and hip abductor strength.
  • Elderly: search for lumbar stenosis and hip disease before assigning pain to the piriformis, and avoid sedating relaxants.
  • Anticoagulation: ultrasound guided fine needle with pressure afterwards, or defer.
  • Renal impairment: avoid NSAIDs, and reduce gabapentin dose.
• Follow up: review at 4 to 6 weeks. Refer to sports medicine, pain medicine, neurology or orthopaedic surgery for failure of 3 months of therapy, neurological deficit, or diagnostic doubt.