Brachial plexus: lower trunk 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 · Brachial plexus: lower trunk injury

Sample item

A 25-year-old man falls from a tree and grabs a branch, suffering a violent upward pull on his arm. He later has a clawed hand, loss of sensation along the medial forearm and hand, and a drooping right eyelid with a small pupil. Which part of the plexus is injured?

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

The answer and the reasoning

A. Lower trunk (C8 and T1), with involvement of T1 sympathetic fibres

Klumpke paralysis follows forced hyperabduction of the arm, which stretches the C8 and T1 roots or the lower trunk. The small muscles of the hand are paralysed, giving a claw hand, and sensation is lost on the medial side of the arm and forearm. Damage to T1 sympathetic fibres causes ipsilateral Horner syndrome (ptosis and miosis).

Option by option

  • A. Lower trunk (C8 and T1), with involvement of T1 sympathetic fibres (correct)

    Correct. A lower trunk lesion produces a claw hand, medial sensory loss and Horner syndrome from T1.

  • B. Posterior cord

    A posterior cord lesion causes wrist drop and weak shoulder abduction, not claw hand or Horner syndrome.

  • C. Upper trunk (C5 and C6)

    An upper trunk lesion (Erb palsy) gives the waiter's tip posture with shoulder abduction and elbow flexion lost.

  • D. Lateral cord

    A lateral cord lesion weakens elbow flexion and forearm pronation, with lateral forearm sensory loss.

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 Anatomy question

What is the answer to this Anatomy question?

The best answer is A, Lower trunk (C8 and T1), with involvement of T1 sympathetic fibres. Klumpke paralysis follows forced hyperabduction of the arm, which stretches the C8 and T1 roots or the lower trunk.

Why is "Posterior cord" not the answer?

A posterior cord lesion causes wrist drop and weak shoulder abduction, not claw hand or Horner syndrome.

Why is "Upper trunk (C5 and C6)" not the answer?

An upper trunk lesion (Erb palsy) gives the waiter's tip posture with shoulder abduction and elbow flexion lost.

Why is "Lateral cord" not the answer?

A lateral cord lesion weakens elbow flexion and forearm pronation, with lateral forearm sensory loss.

What concept does this question test?

It tests Brachial plexus: lower trunk injury in Anatomy. The small muscles of the hand are paralysed, giving a claw hand, and sensation is lost on the medial side of the arm and forearm. Damage to T1 sympathetic fibres causes ipsilateral Horner syndrome (ptosis and miosis).

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 Brachial plexus: lower trunk 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.