Regarding the course and branches of the radial nerve in the upper limb, all of the following statements are correct EXCEPT:

Explanation

## Radial Nerve Course and Motor Supply ### Correct Statements **Key Point:** The radial nerve is indeed the largest terminal branch of the posterior cord (C5–T1) and follows a predictable anatomical course through the upper limb. | Anatomical Segment | Key Features | |---|---| | **Axilla** | Arises from posterior cord; lies medial to axillary artery | | **Spiral groove** | Lies in the groove between lateral and medial heads of triceps; vulnerable to mid-shaft humeral fractures | | **Distal arm** | Pierces lateral intermuscular septum; emerges anterior to lateral epicondyle | | **Forearm** | Divides into superficial (sensory) and deep (motor/PIN) branches | ### Why Option 2 is CORRECT (the exception) **High-Yield:** The radial nerve does NOT innervate pronator teres. Pronator teres is innervated by the **anterior interosseous nerve (AIN)**, a branch of the median nerve. The radial nerve's motor branches in the forearm are: - **Extensor carpi radialis longus (ECRL)** — from the radial nerve proper - **Extensor carpi radialis brevis (ECRB)** — from the posterior interosseous nerve (PIN) - **All other forearm extensors** — from PIN after it passes through supinator **Mnemonic:** **LOAF** = Lateral (thumb) muscles of forearm = Lumbrical, Opponens, Abductor pollicis brevis, Flexor pollicis brevis — all median nerve. Pronator teres is also median (anterior interosseous branch). ### Verification of Other Options 1. **Option 0 (Correct):** Radial nerve arises from posterior cord; C5–T1 is accurate. 2. **Option 1 (Correct):** Spiral groove vulnerability is a classic anatomy fact; mid-shaft humeral fractures cause radial nerve palsy in ~18% of cases. 3. **Option 3 (Correct):** PIN passes through supinator and supplies all extensors (EDC, EIP, EPL, EPB, APL, EIP). ## Clinical Pearl **Radial Nerve Palsy Presentation:** Wrist drop (loss of wrist extension), loss of thumb extension/abduction, sensory loss over dorsal 1st web space. Pronation is preserved because pronator teres (median nerve) and pronator quadratus (AIN) remain intact.