Peripheral nerve injuries: conduction block in neurapraxia: practice question

A Orthopaedics 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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Orthopaedics · Peripheral nerve injuries: conduction block in neurapraxia

Sample item

A patient has a drop of the wrist after prolonged pressure on the arm. Electrical stimulation of the radial nerve proximal to the compression site produces no muscle response, but stimulation distal to it does. What type of injury does this indicate?

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

The answer and the reasoning

A. Neurapraxia

In neurapraxia the axons are intact and only conduction across the injured segment is blocked by local demyelination or ischaemia. The nerve conducts normally distal to the lesion, so recovery is complete and usually takes weeks. In axonotmesis, Wallerian degeneration makes the distal nerve inexcitable after several days.

Option by option

  • A. Neurapraxia (correct)

    Correct. A conduction block with a normal distal response means the axons are intact.

  • B. Complete avulsion of the nerve root

    Root avulsion would show preserved sensory nerve potentials but would not give a localised block at the arm.

  • C. Axonotmesis

    In axonotmesis the distal segment degenerates and stops conducting after a few days.

  • D. Neurotmesis

    Neurotmesis is complete division, and the distal nerve also becomes inexcitable.

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.

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Questions about this Orthopaedics question

What is the answer to this Orthopaedics question?

The best answer is A, Neurapraxia. In neurapraxia the axons are intact and only conduction across the injured segment is blocked by local demyelination or ischaemia.

Why is "Complete avulsion of the nerve root" not the answer?

Root avulsion would show preserved sensory nerve potentials but would not give a localised block at the arm.

Why is "Axonotmesis" not the answer?

In axonotmesis the distal segment degenerates and stops conducting after a few days.

Why is "Neurotmesis" not the answer?

Neurotmesis is complete division, and the distal nerve also becomes inexcitable.

What concept does this question test?

It tests Peripheral nerve injuries: conduction block in neurapraxia in Orthopaedics. The nerve conducts normally distal to the lesion, so recovery is complete and usually takes weeks. In axonotmesis, Wallerian degeneration makes the distal nerve inexcitable after several days.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. 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 Peripheral nerve injuries: conduction block in neurapraxia?

Pair each fracture with its classic complication and nerve injured. Then use the flashcards and the other Orthopaedics 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.