Radial nerve: posterior interosseous syndrome: 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.

Try it

Anatomy · Radial nerve: posterior interosseous syndrome

Sample item

A 45-year-old man develops inability to extend the fingers at the metacarpophalangeal joints after a fracture of the proximal radius. When he extends the wrist it deviates radially. There is no sensory loss. What explains these findings?

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

The answer and the reasoning

C. Posterior interosseous nerve lesion, with extensor carpi radialis longus spared because it is supplied before the nerve enters the supinator

The posterior interosseous nerve is the deep motor branch of the radial nerve that pierces supinator. Extensor carpi radialis longus is supplied by the radial nerve above this level and keeps the wrist extending, though radial deviation occurs because extensor carpi ulnaris is paralysed. The nerve has no cutaneous branch, so sensation is normal.

Option by option

  • A. Anterior interosseous nerve lesion, with wrist extensors supplied by the median nerve

    The anterior interosseous nerve supplies deep flexors, not extensors, and the wrist extensors are radial nerve muscles.

  • B. Superficial radial nerve lesion, with extensor digitorum supplied by the deep branch

    The superficial radial nerve is sensory only, and the extensor digitorum is supplied by the posterior interosseous nerve.

  • C. Posterior interosseous nerve lesion, with extensor carpi radialis longus spared because it is supplied before the nerve enters the supinator (correct)

    Correct. A purely motor branch below the origin of extensor carpi radialis longus explains finger drop with preserved wrist extension and sensation.

  • D. Radial nerve lesion in the spiral groove, with wrist extensors supplied by the superficial branch

    A lesion in the spiral groove would cause complete wrist drop and sensory loss over the dorsum of the hand.

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.

More Anatomy questions

Questions about this Anatomy question

What is the answer to this Anatomy question?

The best answer is C, Posterior interosseous nerve lesion, with extensor carpi radialis longus spared because it is supplied before the nerve enters the supinator. The posterior interosseous nerve is the deep motor branch of the radial nerve that pierces supinator.

Why is "Anterior interosseous nerve lesion, with wrist extensors supplied by…" not the answer?

The anterior interosseous nerve supplies deep flexors, not extensors, and the wrist extensors are radial nerve muscles.

Why is "Superficial radial nerve lesion, with extensor digitorum supplied by…" not the answer?

The superficial radial nerve is sensory only, and the extensor digitorum is supplied by the posterior interosseous nerve.

Why is "Radial nerve lesion in the spiral groove, with wrist extensors suppli…" not the answer?

A lesion in the spiral groove would cause complete wrist drop and sensory loss over the dorsum of the hand.

What concept does this question test?

It tests Radial nerve: posterior interosseous syndrome in Anatomy. Extensor carpi radialis longus is supplied by the radial nerve above this level and keeps the wrist extending, though radial deviation occurs because extensor carpi ulnaris is paralysed. The nerve has no cutaneous branch, so sensation is normal.

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: posterior interosseous syndrome?

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.