Regarding the course and anatomical relations of the radial nerve in the arm, all of the following statements are correct EXCEPT:

Explanation

## Radial Nerve Course — Anatomical Landmarks ### Normal Course of the Radial Nerve The radial nerve follows a characteristic spiral path around the humerus: **Key Point:** The radial nerve originates from the **posterior cord** of the brachial plexus (C5–C8, T1) and is the largest branch of the posterior cord. **High-Yield:** In the **arm**, the radial nerve: 1. Lies in the **radial groove** (spiral groove) on the posterior surface of the humerus 2. Runs between the **medial and lateral heads of triceps** 3. Pierces the **lateral intermuscular septum** proximal to the elbow 4. Enters the **anterior compartment** of the arm 5. Descends **anterior to the brachialis** (not posterior), lying **lateral to the biceps** 6. Reaches the **cubital fossa** where it divides into superficial and deep branches ### Analysis of Each Option | Option | Accuracy | Comment | |--------|----------|----------| | Posterior cord origin (C5–C8, T1) | ✓ Correct | Standard anatomy | | Radial groove between triceps heads | ✓ Correct | Classic landmark for nerve location | | Pierces lateral intermuscular septum | ✓ Correct | Transition from posterior to anterior compartment | | Posterior to brachialis, medial to biceps | ✗ **INCORRECT** | Nerve is **anterior** to brachialis, **lateral** to biceps | **Clinical Pearl:** The radial nerve's vulnerable position in the radial groove explains why **mid-shaft humeral fractures** frequently cause radial nerve injury (Saturday night palsy, crutch palsy). **Mnemonic:** **RAD** = **R**adial groove, **A**nterior (after piercing septum), **D**escends laterally