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Background and Aims Above-knee amputation (AKA) under regional anaesthesia alone can pose multiple challenges to anaesthetists [1]. For AKA, ultrasound-guided selective sciatic nerve, posterior femoral cutaneous nerve (PFCN), femoral, lateral femoral cutaneous, and obturator nerve blockade provide satisfactory anaesthesia.

Methods A 52-year-old woman with ischemic heart disease, atrial fibrillation on therapeutic anticoagulation, chronic kidney disease stage 3, poorly controlled diabetes mellitus, anaemia, and heart failure (ejection fraction 25-30%) was scheduled for an urgent left AKA under regional anaesthesia block due to ascending infection. Considering the high risk, a suprainguinal fascia iliaca block with a perineural catheter was performed under ultrasound. Visualisation of the sciatic nerve and the PFCN was unsuccessful as the neurosonoanatomy was undetectable. The motor response using a nerve stimulator to the suspected sciatic nerve failed, too. 0.5% levobupivacaine 20ml was administered in the area of the suspected nerves using piriformis and other sonoanatomical landmarks. Amputation was carried out without additional analgesia or sedation.

Results Intraoperatively, the sciatic nerve was found to be distorted macroscopically due to liquefactive necrosis. Postoperatively in HDU, her pain control was satisfactory with perineural infusion.

Conclusions The inability to identify the sciatic nerve due to liquefaction is a peculiar encounter in this patient. Still, it hints at an unusual cause for difficult peripheral nerve visualisation and stimulation. Due to the fact that the sciatic and PFCN lie closer when they exit the sciatic foramen under piriformis (2), a sufficient volume of local anaesthetic during sciatic nerve block may spread around and anaesthetise PFCN.