Most common cause of neurological deficit in upper limb is –
**Core Concept**
Posterior interosseous nerve (PIN) palsy is a common cause of neurological deficit in the upper limb, resulting from compression or injury to the deep branch of the radial nerve. This condition leads to weakness of wrist and finger extension.
**Why the Correct Answer is Right**
The PIN supplies the muscles responsible for wrist and finger extension, including the extensor carpi radialis brevis, extensor carpi radialis longus, extensor digitorum, and extensor indicis. Compression of the PIN can occur due to various factors such as ganglion cysts, lipomas, or repetitive strain injuries. This compression can lead to atrophy of the affected muscles, resulting in weakness and loss of function.
**Why Each Wrong Option is Incorrect**
* **Option A:** Suprascapular nerve palsy is a condition that affects the muscles of the rotator cuff, particularly the supraspinatus and infraspinatus. While it can cause shoulder weakness, it is not the most common cause of neurological deficit in the upper limb.
* **Option B:** Ulnar nerve palsy typically presents with symptoms such as claw hand, weakness of the intrinsic muscles of the hand, and sensory changes in the little finger and ring finger. It is not the most common cause of neurological deficit in the upper limb.
* **Option C:** Median nerve palsy can cause weakness of the thenar muscles, leading to difficulty in opposition of the thumb. While it can affect the upper limb, it is not the most common cause of neurological deficit.
**Clinical Pearl / High-Yield Fact**
A key clinical feature of PIN palsy is the preservation of thumb extension, as the extensor pollicis longus muscle is supplied by a separate branch of the radial nerve. This can be used as a useful clinical clue to diagnose PIN palsy.
**Correct Answer:** C.