Lower limb: lumbar disc and nerve roots: 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 · Lower limb: lumbar disc and nerve roots

Sample item

A 38-year-old man lifts a heavy box and develops back pain radiating down the posterolateral thigh and lateral leg to the dorsum of the foot, with weak great toe extension. A posterolateral disc prolapse is suspected. Which level and root are most likely involved?

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

The answer and the reasoning

C. L4-L5 disc compressing the L5 root

A posterolateral prolapse compresses the root that traverses the disc space on its way to exit below, so the L4-L5 disc affects the L5 root. L5 compression causes pain in the lateral leg and dorsum of foot with weak extensor hallucis longus. The L4 root has already left the canal above the L4-L5 disc and is affected only by a far-lateral prolapse.

Option by option

  • A. L4-L5 disc compressing the L4 root

    The L4 root exits above the L4-L5 disc and is affected only by a far-lateral prolapse.

  • B. L5-S1 disc compressing the S1 root

    An L5-S1 prolapse compresses S1, which causes lateral foot pain, weak plantar flexion and an absent ankle jerk.

  • C. L4-L5 disc compressing the L5 root (correct)

    The L5 root crosses the posterior aspect of the L4-L5 disc and is compressed by a posterolateral prolapse.

  • D. L3-L4 disc compressing the L4 root

    An L3-L4 prolapse compresses L4, causing medial leg pain, weak knee extension and a reduced knee jerk.

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 C, L4-L5 disc compressing the L5 root. A posterolateral prolapse compresses the root that traverses the disc space on its way to exit below, so the L4-L5 disc affects the L5 root.

Why is "L4-L5 disc compressing the L4 root" not the answer?

The L4 root exits above the L4-L5 disc and is affected only by a far-lateral prolapse.

Why is "L5-S1 disc compressing the S1 root" not the answer?

An L5-S1 prolapse compresses S1, which causes lateral foot pain, weak plantar flexion and an absent ankle jerk.

Why is "L3-L4 disc compressing the L4 root" not the answer?

An L3-L4 prolapse compresses L4, causing medial leg pain, weak knee extension and a reduced knee jerk.

What concept does this question test?

It tests Lower limb: lumbar disc and nerve roots in Anatomy. L5 compression causes pain in the lateral leg and dorsum of foot with weak extensor hallucis longus. The L4 root has already left the canal above the L4-L5 disc and is affected only by a far-lateral prolapse.

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 Lower limb: lumbar disc and nerve roots?

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.