This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
Wrist drop is due to injury of - 
Select and explain. 
A. Ulnar nerve, B. Radial nerve, C. Median nerve, D. Musculocutaneous nerve
B: Radial nerve
Answer: B: Radial nerve 
Explanation: Radial nerve injury
-        High radial nerve palsy- Injury above the spiral groove.
o   Paralysis of all muscles supplied by radial nerve.
o   Clinical features

Wrist drop, finger drop, thumb drop
Extension affected of- elbow, wrist, thumb and fingers
Sensation affected of- posterior surface of arm and forearm and lower lateral half of forearm.

-        Low radial nerve palsy- Injury below the spiral groove.
o   Type I- Injury between spiral groove and elbow.

Elbow extensors are spared- Triceps and Anconeus.
Wrist, thumb and finger extensors paralysed- wrist drop, thumb drop, finger drop.
Loss of sensation on dorsal side of first web space.

o   Type II- Injury below the elbow joint.

Elbow and wrist extensors spared
Thumb and finger extensors paralysed.(extensor digitorum, extensor digiti minimi, extensor indicis, extensor pollicis longus, extensor pollicis brevis)- Thumb drop and finger drop.
Loss of sensation on dorsal side of first web space.