Question

A small boy with multiple fracture of Humerus following which there is loss of sensation over lateral side of forearm, difficulty in flexion of elbow & supination of forearm.

• A. Musculocutaneous nerve
• B. Median nerve
• C. Median nerve
• D. Radial nerve

Answer 1

The Correct Option is A

The clinical triad in this case -- loss of lateral forearm sensation, weak elbow flexion, and weak supination -- points to injury of the $\text{Musculocutaneous nerve}$ (roots $C_5$--$C_7$).

Anatomy of the Musculocutaneous nerve:
- Arises from the lateral cord of the brachial plexus
- Motor: coracobrachialis, biceps brachii, brachialis
- Sensory: continues as the lateral cutaneous nerve of forearm, supplying the lateral aspect of the forearm

Functional correlation:
- Biceps brachii = primary supinator + elbow flexor
- Brachialis = elbow flexor
- Lateral cutaneous nerve of forearm = lateral forearm sensation

Why not others?
- Median nerve injury: loss of thumb opposition, pronation, wrist flexion; no lateral forearm numbness
- Axillary nerve: deltoid weakness, lateral arm numbness
- Radial nerve: wrist drop, finger drop

\[\boxed{\text{Musculocutaneous nerve}}\]