Upper limb: posterior interosseous nerve: 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 · Upper limb: posterior interosseous nerve

Sample item

A 40-year-old woman has a slowly growing lipoma near the head of the radius. She cannot extend the metacarpophalangeal joints of her fingers and thumb, but when asked to extend the wrist it deviates radially. Sensation over the dorsum of the hand is normal. Which statement best explains these findings?

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

The answer and the reasoning

B. The deep radial branch is compressed in the supinator, sparing extensor carpi radialis longus

The posterior interosseous nerve, the continuation of the deep radial branch, passes through supinator and supplies the finger and thumb extensors and extensor carpi ulnaris. Extensor carpi radialis longus is supplied before the division, so wrist extension remains with radial deviation. As it is purely motor, there is no sensory loss, which separates this from a high radial nerve lesion.

Option by option

  • A. The radial nerve is injured in the spiral groove of the humerus

    A spiral groove lesion causes full wrist drop and numbness over the first dorsal web space.

  • B. The deep radial branch is compressed in the supinator, sparing extensor carpi radialis longus (correct)

    Correct. The pattern of finger drop, radial deviation on wrist extension and no sensory loss is typical of posterior interosseous palsy.

  • C. The ulnar nerve is compressed behind the medial epicondyle

    An ulnar nerve lesion produces claw hand and ulnar-sided sensory loss, with intact finger extension.

  • D. The anterior interosseous nerve is compressed between the heads of pronator teres

    An anterior interosseous lesion weakens flexion of the thumb and index terminal phalanges and does not affect extension.

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 B, The deep radial branch is compressed in the supinator, sparing extensor carpi radialis longus. The posterior interosseous nerve, the continuation of the deep radial branch, passes through supinator and supplies the finger and thumb extensors and extensor carpi ulnaris.

Why is "The radial nerve is injured in the spiral groove of the humerus" not the answer?

A spiral groove lesion causes full wrist drop and numbness over the first dorsal web space.

Why is "The ulnar nerve is compressed behind the medial epicondyle" not the answer?

An ulnar nerve lesion produces claw hand and ulnar-sided sensory loss, with intact finger extension.

Why is "The anterior interosseous nerve is compressed between the heads of pr…" not the answer?

An anterior interosseous lesion weakens flexion of the thumb and index terminal phalanges and does not affect extension.

What concept does this question test?

It tests Upper limb: posterior interosseous nerve in Anatomy. Extensor carpi radialis longus is supplied before the division, so wrist extension remains with radial deviation. As it is purely motor, there is no sensory loss, which separates this from a high radial nerve lesion.

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 Upper limb: posterior interosseous nerve?

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.