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Interscalene block distribution — FRCA Primary MCQ

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HardAnatomyInterscalene block distributionFRCA Primary

After an interscalene block for shoulder surgery, the patient has good shoulder analgesia but preserved sensation in the ulnar border of the hand. Which anatomical explanation is best?

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Correct answer: B — Lower trunk is relatively spared

Interscalene block targets roots and trunks of the brachial plexus, but the lower trunk C8-T1 is often relatively spared, preserving ulnar distribution sensation. The median nerve is a terminal branch of the brachial plexus. The musculocutaneous nerve is from the lateral cord, not the sacral plexus. This is why interscalene block is excellent for shoulder surgery but less reliable for hand surgery.

Reference: RCoA Primary FRCA Syllabus; regional anaesthesia anatomy texts