Radial nerve: level of injury: practice question

A Anatomy question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Anatomy · Radial nerve: level of injury

Sample item

Two patients have wrist drop. Patient A fell asleep with the arm hanging over a chair back and has compression of the nerve in the spiral groove of the humerus. Patient B has used a badly fitted crutch pressed into the axilla for several weeks. Which finding is expected in patient B but not in patient A?

AWeakness of finger extension at the metacarpophalangeal jointsBWeakness of wrist extensionCSensory loss over the dorsum of the first web spaceDWeakness of elbow extension from paralysis of triceps brachii

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

D. Weakness of elbow extension from paralysis of triceps brachii

The radial nerve gives its branches to the long and medial heads of triceps in the axilla and upper arm, before it enters the spiral groove. A midshaft lesion therefore spares elbow extension, while a high lesion in the axilla paralyses triceps as well as every muscle below. Wrist drop and loss of sensation over the first dorsal web space occur in both.

Option by option

A. Weakness of finger extension at the metacarpophalangeal joints
Extensor digitorum is supplied by the posterior interosseous nerve, so finger drop occurs in both patients.
B. Weakness of wrist extension
Wrist extensors are supplied below the groove, so both patients lose wrist extension.
C. Sensory loss over the dorsum of the first web space
The superficial radial nerve is a continuation of the radial nerve below the groove, so sensory loss occurs in both.
D. Weakness of elbow extension from paralysis of triceps brachii (correct)
Correct. The triceps branches arise proximal to the groove and are affected only by the axillary lesion.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is D, Weakness of elbow extension from paralysis of triceps brachii. The radial nerve gives its branches to the long and medial heads of triceps in the axilla and upper arm, before it enters the spiral groove.

Why is "Weakness of finger extension at the metacarpophalangeal joints" not the answer?

Extensor digitorum is supplied by the posterior interosseous nerve, so finger drop occurs in both patients.

Why is "Weakness of wrist extension" not the answer?

Wrist extensors are supplied below the groove, so both patients lose wrist extension.

Why is "Sensory loss over the dorsum of the first web space" not the answer?

The superficial radial nerve is a continuation of the radial nerve below the groove, so sensory loss occurs in both.

What concept does this question test?

It tests Radial nerve: level of injury in Anatomy. A midshaft lesion therefore spares elbow extension, while a high lesion in the axilla paralyses triceps as well as every muscle below. Wrist drop and loss of sensation over the first dorsal web space occur in both.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Radial nerve: level of injury?

Learn every nerve by its route, its muscles and what a lesion looks like at the bedside. That one habit answers a large share of questions. Then use the flashcards and the other Anatomy questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.