Popliteal Block Coverage — FRCA Final MCQ

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ModerateRegional AnaesthesiaPopliteal Block CoverageFRCA Final

A 40-year-old man is undergoing ankle arthroscopy. An ultrasound-guided popliteal sciatic nerve block is performed with 20 mL of 0.375% ropivacaine. Ultrasound confirms local anaesthetic spread around both the tibial and common fibular divisions, and the block is clinically successful. Which cutaneous area will remain unanaesthetised by this block alone?

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Correct answer: B — Skin immediately anterior to the medial malleolus

A successful popliteal sciatic block anaesthetises the tibial and common fibular divisions. The tibial nerve covers the plantar forefoot; the deep fibular nerve supplies the first dorsal web space; the sural nerve supplies the lateral foot; and the superficial fibular nerve supplies most of the dorsum. The skin immediately anterior to the medial malleolus is supplied by the saphenous nerve, a terminal sensory branch of the femoral nerve, so it is outside the popliteal sciatic block. Clinical evidence demonstrates anteromedial ankle breakthrough pain after popliteal sciatic block when the saphenous nerve is not effectively blocked. A supplementary saphenous nerve block is therefore required when medial ankle coverage is needed.

Reference: Bjørn S, Wong WY, Baas J, et al. The Importance of the Saphenous Nerve Block for Analgesia Following Major Ankle Surgery: A Randomized, Controlled, Double-Blind Study. Regional Anesthesia and Pain Medicine. 2018;43(5):474-479. https://pubmed.ncbi.nlm.nih.gov/29667940/