Ape hand deformity, characterized by an inability to oppose the thumb, is caused by compression or injury to… - KGMU 2023

KGMU 2023

Applied Anatomy

Easy

Appeared in: KGMU 2023

Explanation

The median nerve is responsible for the motor innervation of the thenar muscles, which include the opponens pollicis, abductor pollicis brevis, and flexor pollicis brevis.
These muscles are essential for the opposition of the thumb, a movement that allows the thumb to touch the tips of the other fingers.
Injury or compression of the median nerve leads to paralysis and subsequent atrophy (wasting) of the thenar muscles.
This muscle wasting causes the thenar eminence to flatten, and the thumb falls back in line with the other fingers, losing its ability to oppose. This clinical sign is known as 'Ape Hand Deformity'.

Option A: Injury to the radial nerve affects the extensor muscles of the forearm, not the thenar muscles responsible for thumb opposition.
Option C: Ulnar nerve injury affects the intrinsic muscles of the hand, particularly those controlling the 4th and 5th digits, leading to a different type of deformity.
Option D: The axillary nerve innervates muscles around the shoulder joint, and its injury does not cause hand deformities.

Visual 1: Diagram - A clear illustration comparing a normal hand with a hand showing Ape Hand Deformity, highlighting the atrophied thenar eminence.
Visual 2: Anatomical Chart - A chart showing the pathway of the median, ulnar, and radial nerves in the arm and hand, with the muscles they innervate clearly labeled.
Visual 3: Comparative Table - An infographic visually comparing the classic hand deformities associated with major nerve injuries: Ape Hand (Median), Claw Hand (Ulnar), and Wrist Drop (Radial).

Clinical Relevance

Nursing practice connection: Knowing Peripheral Nerve Injury and Associated Deformities helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses must be able to recognize specific hand deformities like Ape Hand as it points directly to a significant neurological deficit (median nerve palsy), requiring prompt assessment and physician notification.
A thorough neurological assessment for a patient with suspected median nerve injury includes testing motor function (thumb opposition), sensory function (sensation in the thumb, index, middle, and half of the ring finger), and observing for thenar muscle wasting.
What if? If a patient with a wrist fracture develops an Ape Hand deformity and also complains of numbness and tingling in the little finger, it suggests a more complex injury involving both the median and ulnar nerves, which requires urgent and comprehensive evaluation.

How to Approach the Question

First, identify the key clinical sign described in the question stem: 'Ape hand deformity' and 'inability to oppose the thumb'.
Recall the anatomy and function of the hand muscles. The movement of thumb opposition is primarily controlled by the thenar muscles.
Connect the muscles to their nerve supply. Remember that the median nerve innervates the thenar muscle group.
Therefore, a deficit in thumb opposition (Ape Hand) points directly to an injury of the median nerve.
Eliminate the other options by recalling the classic signs of their injury: Radial nerve -> Wrist drop, Ulnar nerve -> Claw hand, Axillary nerve -> Shoulder abduction weakness.

Concept Tested & Keywords

Concept Tested: Peripheral Nerve Injury and Associated Deformities
Stem keywords: Ape hand deformity, inability to oppose the thumb, nerve compression, nerve injury
Lead-in keywords: which nerve
Negative lead-in flag: false

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