Fracture of the humerus at the mid-shaft is likely to cause injury to which of the following nerves?

Appeared in: UPPSC-2021

Explanation

The radial nerve is the correct answer because it runs in the spiral groove on the posterior aspect of the mid-shaft of the humerus.
This close anatomical relationship makes the radial nerve highly susceptible to injury during a mid-shaft humeral fracture.
A classic sign of injury to the radial nerve at this level is 'wrist drop,' which is the inability to extend the wrist and fingers.

Option A: The musculocutaneous nerve supplies the muscles in the anterior compartment of the arm (like biceps brachii) and is not typically injured by a mid-shaft humeral fracture.
Option B: The ulnar nerve passes down the medial side of the arm and is most vulnerable to injury behind the medial epicondyle of the humerus, often referred to as the 'funny bone'.
Option C: The median nerve runs more anteriorly in the arm and is most commonly injured in supracondylar fractures of the humerus, which occur just above the elbow.

Clinical Relevance

Nursing practice connection: Knowing Nerve injury associated with humeral fractures helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
A primary nursing responsibility for a patient with a humeral fracture is performing frequent neurovascular assessments (checking circulation, motion, and sensation) to detect nerve or vessel compromise early.
Recognizing the signs of radial nerve palsy, such as wrist drop, allows for prompt notification of the physician and initiation of appropriate interventions, like splinting, to prevent contractures.
What if? If the fracture was at the surgical neck of the humerus instead of the mid-shaft, the nurse's assessment would focus on the axillary nerve. The key test would be checking for the ability to abduct the arm (deltoid muscle function) and assessing sensation over the 'sergeant's patch' area on the shoulder.

How to Approach the Question

First, identify the key anatomical location mentioned in the question: 'mid-shaft' of the 'humerus'.
Next, recall the major nerves of the upper arm and their specific pathways in relation to the humerus bone.
Associate the radial nerve with its path in the spiral groove on the posterior surface of the humeral mid-shaft.
Evaluate the other options: Musculocutaneous (anterior arm), Ulnar (medial epicondyle), and Median (supracondylar area).
Conclude that due to its direct contact with the bone at the mid-shaft, the radial nerve is the most likely nerve to be injured.
Select the option corresponding to the radial nerve.

Concept Tested & Keywords

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E6 Anatomy Applied Ashalatha 4e p. 435-437

E6 Anatomy Grays 43e Vol 2 Part 2 p. 114-116

E6 Anatomy Workbook HumanAnatomy Vol 1 p. 29-31

Practise the full UPPSC-2021

Attempt every question from this paper in a timed mock, then review the full solution for each one.