Wrist drop is due to injury of -

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.