Sciatic nerve block following piriformis injection under ultrasound and nerve stimulator guidance-a case report

Sheila Clarke, S Muthukrishnan, S. Kanakarajan

Research output: Contribution to journalArticlepeer-review


Purpose/Objective: Piriformis syndrome is thought to cause of 6-8% of sciatica. Injection of local anaesthetic and steroid into piriformis muscle is an established treatment option. A combined technique of ultrasound with motor stimulation has been advocated for accurate confirmation of piriformis pain and avoidance of sciatic nerve block. We report a case of sciatic nerve block despite taking the above precautions. Materials and Methods: The patient was positioned prone with intravenous access and standard monitoring in place. A pillow under the pelvis optimised piriformis visualization. A 2-5 Hz curvilinear probe placed horizontally over the posterior superior iliac spine was moved downwards and laterally to identify piriformis and the sciatic nerve. Under ultrasound guidance a 100mm insulated needle was passed into piriformis. A current of 2mA resulted in contraction of piriformis and pain. No muscle contractions corresponding to tibial or peroneal nerve stimulation were observed. 10ml of 0.25% levobupivacaine and 80mg of triamcinolone were injected. Results: 30 minutes after injection, a sciatic nerve block became obvious. This resolved completely after 8 hours. The patient reported a 70% reduction in her presenting symptoms. Conclusions: Nerve localisation studies have shown that an absence of muscle contraction at 1-2m. A stimulation indicates that the nerve is 0.5-1cm away from the needle tip. However, MRI studies report that a volume of 10mls is required for even spread within the muscle and in 10% of the population, the peroneal portion of the sciatic nerve traverses piriformis. In our case, injectate spread is likely to have caused the sciatic block.
Original languageEnglish
Pages (from-to)E166-E167
Number of pages2
JournalRegional Anesthesia and Pain Medicine
Issue number5
Publication statusPublished - Sep 2013


  • anesthetic agent
  • case report
  • human
  • injection
  • levobupivacaine
  • monitoring
  • muscle
  • muscle contraction
  • needle
  • nerve
  • nerve block
  • nerve stimulation
  • nerve stimulator
  • nuclear magnetic resonance imaging
  • pain
  • patient
  • pelvis
  • peroneus nerve
  • piriformis syndrome
  • population
  • regional anesthesia
  • sciatic nerve
  • sciatica
  • society
  • spine
  • steroid
  • stimulation
  • therapy
  • triamcinolone
  • ultrasound


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