After an axillary brachial plexus block performed with a nerve stimulator, the patient has complete anaesthesia of the hand and medial forearm but cannot flex the elbow against gravity and has absent biceps contraction. Which nerve was most likely missed, and why?

• A Radial nerve, because it lies posterior to the axillary artery outside the sheath
• B Ulnar nerve, because it lies superficial to the artery and is poorly stimulated
• C Median nerve, because it runs deep to the fascia between artery and vein
• D Musculocutaneous nerve, because it leaves the sheath proximal to the axilla within coracobrachialis ✓

Explanation

The musculocutaneous nerve branches from the lateral cord and exits the axillary sheath early, piercing coracobrachialis before entering the axilla. It supplies biceps, brachialis and coracobrachialis plus the lateral cutaneous nerve of forearm, so an axillary block commonly spares elbow flexion and sensation over the lateral forearm. Adding a separate subcutaneous injection into the body of coracobrachialis covers it. Radial, median and ulnar nerves remain around the axillary artery within the block territory.

Reference: Hadzic's Peripheral Nerve Blocks and Anatomy for Ultrasound-Guided Regional Anesthesia, 2nd ed.

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Written and medically reviewed by the StethoPrep medical team.