A patient with leprosy presents with clumsiness of hand. His ulnar nerve is affected. Clumsiness is due to palsy of which muscle –
**Core Concept**
Leprosy, a chronic bacterial infection caused by *Mycobacterium leprae*, can lead to peripheral neuropathy, particularly affecting the ulnar nerve, resulting in motor and sensory deficits. The ulnar nerve innervates several muscles in the forearm and hand, controlling fine motor movements.
**Why the Correct Answer is Right**
The ulnar nerve controls the intrinsic muscles of the hand, including the interosseous muscles, lumbricals, and the hypothenar muscles. The primary muscle responsible for fine motor movements of the hand, particularly the opposition of the thumb, is the adductor pollicis, which is innervated by the ulnar nerve. Clumsiness of the hand in this patient is due to the palsy of the adductor pollicis muscle, leading to weakness in thumb opposition.
**Why Each Wrong Option is Incorrect**
* **Option A:** The flexor carpi ulnaris muscle, also innervated by the ulnar nerve, is primarily responsible for wrist flexion and forearm rotation, not fine motor movements of the hand.
* **Option B:** The flexor digitorum profundus muscle, innervated by the ulnar nerve, is responsible for finger flexion, but not specifically thumb opposition.
* **Option C:** The extensor digitorum muscle, innervated by the radial nerve, is responsible for finger extension, not fine motor movements of the hand.
**Clinical Pearl / High-Yield Fact**
The ulnar nerve is commonly affected in leprosy due to its susceptibility to compression and damage in the arm and forearm, leading to weakness and clumsiness of the hand.
**Correct Answer:** D. Adductor pollicis.