An axillary brachial plexus block provides excellent anaesthesia for hand and forearm surgery, but a specific terminal branch is consistently missed because it has already left the neurovascular sheath at the coracobrachialis muscle. Failure is noticed when the patient feels the tourniquet or incision over the lateral forearm. Which nerve is this?

• A Medial cutaneous nerve of forearm
• B Radial nerve
• C Musculocutaneous nerve ✓
• D Ulnar nerve

Explanation

The musculocutaneous nerve leaves the brachial plexus sheath proximally, piercing the coracobrachialis muscle, so it lies outside the perivascular compartment when an axillary block is performed. It supplies the biceps and brachialis and continues as the lateral cutaneous nerve of the forearm, explaining failure of lateral forearm anaesthesia. It must be blocked separately by injection into the substance of coracobrachialis. The radial, ulnar, and medial cutaneous nerves all travel within the axillary sheath alongside the axillary artery and are reliably blocked.

Reference: Hadzic's Peripheral Nerve Blocks and Anatomy for Ultrasound-Guided Regional Anesthesia, 3rd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.