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

Question

Accepted Answer

B. The radial nerve descends posterior to the brachialis muscle and medial to the biceps before reaching the cubital fossa. ## 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

Answer

A. The radial nerve pierces the lateral intermuscular septum proximal to the elbow and enters the anterior compartment of the arm

Answer

C. The radial nerve lies in the radial groove on the posterior surface of the humerus between the medial and lateral heads of triceps

Answer

D. The radial nerve arises from the posterior cord of the brachial plexus (C5–C8, T1)

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

Analysis of Each Option

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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