Paralysis of which nerve produces 'Ape thumb deformity?

Question

Question

This question was previously asked in

KGMU Nursing Officer 2023 Memory-Based Previous Year Paper

Answer 1

Correct Answer: Median Nerve

Rationale:

The "Ape thumb deformity" is caused by paralysis of the median nerve. This deformity is characterized by the inability to oppose or abduct the thumb, resulting in the thumb being aligned in the same plane as the fingers, resembling an "ape-like" appearance.
The median nerve is responsible for innervating muscles in the anterior forearm and some intrinsic muscles of the hand, including the thenar muscles, which control thumb movements like opposition and abduction.
Damage to the median nerve can occur due to trauma, compression (e.g., carpal tunnel syndrome), or systemic diseases like diabetes.

Additional Information:

The thenar muscles, which include the abductor pollicis brevis, flexor pollicis brevis, and opponens pollicis, are primarily controlled by the median nerve. Paralysis of these muscles leads to functional impairment of thumb movements.
Other symptoms of median nerve damage include sensory loss in the thumb, index finger, middle finger, and the radial half of the ring finger, as well as weakness in forearm pronation and wrist flexion.

Explanation of Other Options:

Axillary Nerve

Rationale: The axillary nerve innervates the deltoid and teres minor muscles, which are involved in shoulder abduction and external rotation. Damage to this nerve results in shoulder weakness and sensory loss over the deltoid region but does not affect thumb movements.

Radial Nerve

Rationale: The radial nerve controls the muscles responsible for wrist and finger extension. Paralysis of this nerve results in "wrist drop" but does not cause the "ape thumb deformity," as it does not innervate the thenar muscles.

Ulnar Nerve

Rationale: The ulnar nerve innervates many intrinsic hand muscles, including the hypothenar muscles and the interossei. Damage to this nerve can cause claw hand deformity but does not lead to "ape thumb deformity," as it does not primarily innervate the thenar muscles.

Conclusion:

The median nerve is responsible for the proper functioning of the thenar muscles, which are essential for thumb movements like opposition and abduction. Paralysis of this nerve results in "ape thumb deformity," making it the correct answer among the given options.