The radial nerve emerges from the posterior cord of the brachial plexus and spirals around the shaft of the humerus in the radial groove. At what level does the radial nerve typically exit the spiral groove to enter the anterior compartment of the arm?

## Radial Nerve Course Through the Arm **Key Point:** The radial nerve spirals posteriorly around the humerus within the radial groove (also called the spiral groove or musculospiral groove) and exits to enter the anterior compartment at the junction of the middle and distal thirds of the humerus. ### Anatomical Sequence 1. **Origin:** Posterior cord of the brachial plexus (C5, C6, C7, C8, T1) 2. **Course in spiral groove:** Travels with the profunda brachii artery (superior radial collateral artery) 3. **Exit point:** Middle-to-distal third junction — pierces the lateral intermuscular septum 4. **Anterior compartment:** Descends between brachialis and brachioradialis muscles 5. **Forearm entry:** Passes anterior to the lateral epicondyle and divides into superficial and deep branches **High-Yield:** This exit point is clinically significant because: - Fractures of the distal humerus (supracondylar fractures) occur below this point and typically spare the radial nerve - Mid-shaft humeral fractures are the classic site of radial nerve injury - The nerve is vulnerable in the spiral groove to compression or stretch injury **Clinical Pearl:** Fractures at the junction of middle and distal thirds of the humerus have the highest risk of radial nerve injury because the nerve is tethered in the spiral groove at this exact location. ### Mnemonic **RADIAL GROOVE EXITS:** **M**iddle-to-**D**istal junction = **MD** (Medical Doctor — remember the initials!) ## Why This Matters for NEET PG The exact exit point of the radial nerve from the spiral groove is a high-yield anatomical landmark tested frequently in anatomy and orthopaedic surgery sections. It correlates with fracture patterns and nerve injury risk.