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Double Crush Neuropathy — FRCA Final MCQ

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HardRegional AnaesthesiaDouble Crush NeuropathyFRCA Final

A 55-year-old man with diabetes and peripheral neuropathy is having foot surgery under a popliteal sciatic nerve block. Post-operatively he cannot dorsiflex his foot (foot drop). This was not present pre-operatively. The pre-existing peripheral neuropathy is relevant because:

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Correct answer: E — Pre-existing neural compromise increases susceptibility to further nerve injury from block (double crush phenomenon)

The 'double crush' hypothesis explains why patients with pre-existing neuropathy (diabetic, chemotherapy-induced, hereditary) are more susceptible to nerve injury from peripheral nerve blocks. A nerve already compromised at one site (e.g., by diabetes) is more vulnerable to a second insult (local anaesthetic neurotoxicity, mechanical needle trauma, ischaemia from adrenaline). Risk mitigation: use lower concentrations of LA, avoid adrenaline-containing solutions, use short-acting agents, and ensure informed consent includes discussion of the increased risk.

Reference: RCOA – 2023 – Regional anaesthesia complications; Barrington MJ – 2020 – Nerve injury after PNB