Wrist drop is due to injury to –
**Core Concept**
Wrist drop, also known as radial nerve palsy, is a condition characterized by the inability to extend the wrist due to weakness or paralysis of the extensor muscles of the forearm. This condition is often caused by trauma or injury to the radial nerve.
**Why the Correct Answer is Right**
The radial nerve is responsible for innervating the extensor muscles of the forearm, including the extensor carpi radialis brevis and extensor digitorum. Injury to the radial nerve at the level of the radial groove in the humerus can lead to wrist drop. This is because the radial nerve is responsible for transmitting motor signals from the central nervous system to the muscles of the forearm, allowing for wrist extension.
**Why Each Wrong Option is Incorrect**
* **Option A:** Injury to the ulnar nerve would result in weakness or paralysis of the intrinsic muscles of the hand, leading to symptoms such as claw hand or interosseous muscle weakness, not wrist drop.
* **Option B:** Injury to the median nerve would result in weakness or paralysis of the flexor muscles of the forearm and thumb, leading to symptoms such as thenar muscle weakness or thumb opposition weakness, not wrist drop.
* **Option C:** Injury to the brachial artery would result in ischemia or infarction of the forearm and hand, leading to symptoms such as pain, pallor, pulselessness, or paresthesia, not wrist drop.
**Clinical Pearl / High-Yield Fact**
It is essential to note that wrist drop can also be caused by other conditions such as polyneuropathy, poliomyelitis, or peripheral neuropathy. A thorough history and physical examination are necessary to determine the underlying cause of wrist drop.
**Correct Answer: D. Injury to the radial nerve.**