Nerve injuries: EMG timing: 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 · Nerve injuries: EMG timing

Sample item

A patient has foot drop after a knee dislocation. A nerve conduction study done on day 3 is normal below the injury. When do fibrillation potentials typically appear on EMG after a complete axonotmesis?

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

The answer and the reasoning

B. About 3 weeks after injury

Fibrillation potentials and positive sharp waves indicate denervation and take about 3 weeks to appear on EMG. Early studies can therefore be normal or show only reduced recruitment. Studies repeated at 3 weeks or later help distinguish neurapraxia from axonotmesis.

Option by option

  • A. Within the first hour

    Denervation potentials do not appear in the first hour.

  • B. About 3 weeks after injury (correct)

    Correct. EMG denervation changes become detectable at about 3 weeks.

  • C. They never appear in axonotmesis

    Fibrillation potentials are the hallmark of denervation after axonotmesis.

  • D. After 6 months

    Waiting 6 months is far too late to guide management.

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 B, About 3 weeks after injury. Fibrillation potentials and positive sharp waves indicate denervation and take about 3 weeks to appear on EMG.

Why is "Within the first hour" not the answer?

Denervation potentials do not appear in the first hour.

Why is "They never appear in axonotmesis" not the answer?

Fibrillation potentials are the hallmark of denervation after axonotmesis.

Why is "After 6 months" not the answer?

Waiting 6 months is far too late to guide management.

What concept does this question test?

It tests Nerve injuries: EMG timing in Orthopaedics. Early studies can therefore be normal or show only reduced recruitment. Studies repeated at 3 weeks or later help distinguish neurapraxia from axonotmesis.

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 Nerve injuries: EMG timing?

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.