Brachial plexus: posterior cord: 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: posterior cord

Sample item

A man has a stab wound in the axilla. He has wrist drop, weak abduction of the arm beyond 15 degrees, and weak adduction and internal rotation of the arm. Biceps function and the intrinsic hand muscles are normal. Which part of the plexus is injured?

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

The answer and the reasoning

D. Posterior cord

The posterior cord gives the upper and lower subscapular nerves, the thoracodorsal nerve, the axillary nerve and the radial nerve. A lesion therefore paralyses the extensors of the wrist and fingers, deltoid and teres minor, subscapularis, teres major and latissimus dorsi. Biceps is supplied by the lateral cord and intrinsic hand muscles by the medial cord.

Option by option

  • A. Medial cord

    A medial cord lesion produces a claw hand and medial sensory loss.

  • B. Lateral cord

    A lateral cord lesion weakens biceps, brachialis and coracobrachialis through the musculocutaneous nerve.

  • C. Upper trunk

    An upper trunk lesion causes Erb palsy with weak abduction and elbow flexion but no wrist drop.

  • D. Posterior cord (correct)

    Correct. The combination of radial, axillary and subscapular nerve deficits localises the lesion to the posterior cord.

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 D, Posterior cord. The posterior cord gives the upper and lower subscapular nerves, the thoracodorsal nerve, the axillary nerve and the radial nerve.

Why is "Medial cord" not the answer?

A medial cord lesion produces a claw hand and medial sensory loss.

Why is "Lateral cord" not the answer?

A lateral cord lesion weakens biceps, brachialis and coracobrachialis through the musculocutaneous nerve.

Why is "Upper trunk" not the answer?

An upper trunk lesion causes Erb palsy with weak abduction and elbow flexion but no wrist drop.

What concept does this question test?

It tests Brachial plexus: posterior cord in Anatomy. A lesion therefore paralyses the extensors of the wrist and fingers, deltoid and teres minor, subscapularis, teres major and latissimus dorsi. Biceps is supplied by the lateral cord and intrinsic hand muscles by the medial cord.

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 Brachial plexus: posterior cord?

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.