Spine: disc prolapse: 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 · Spine: disc prolapse

Sample item

A 40-year-old man has back pain and weakness of great toe dorsiflexion, with numbness on the dorsum of the foot and lateral leg. The ankle jerk is normal. Which disc prolapse is the most likely cause?

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

The answer and the reasoning

B. Posterolateral prolapse at L4-L5 compressing the L5 root

A posterolateral lumbar disc prolapse usually compresses the root that exits one level below, as it crosses the disc: L4-L5 affects L5 and L5-S1 affects S1. L5 weakness affects great toe extension and foot dorsiflexion, with sensory loss on the dorsum of the foot, whereas S1 compression causes weak plantar flexion, lateral foot numbness and loss of the ankle jerk.

Option by option

  • A. Central prolapse at L2-L3 compressing the L3 root

    L3 compression causes weakness of the quadriceps and a diminished knee jerk.

  • B. Posterolateral prolapse at L4-L5 compressing the L5 root (correct)

    Correct. L5 compression gives weak great toe dorsiflexion, dorsal foot numbness and a preserved ankle jerk.

  • C. Posterolateral prolapse at L5-S1 compressing the S1 root

    S1 compression gives a diminished ankle jerk and weak plantar flexion.

  • D. Prolapse at L3-L4 compressing the L4 root

    L4 compression causes weakness of ankle dorsiflexion and inversion, numbness over the medial leg and a diminished 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 Orthopaedics question

What is the answer to this Orthopaedics question?

The best answer is B, Posterolateral prolapse at L4-L5 compressing the L5 root. A posterolateral lumbar disc prolapse usually compresses the root that exits one level below, as it crosses the disc: L4-L5 affects L5 and L5-S1 affects S1.

Why is "Central prolapse at L2-L3 compressing the L3 root" not the answer?

L3 compression causes weakness of the quadriceps and a diminished knee jerk.

Why is "Posterolateral prolapse at L5-S1 compressing the S1 root" not the answer?

S1 compression gives a diminished ankle jerk and weak plantar flexion.

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

L4 compression causes weakness of ankle dorsiflexion and inversion, numbness over the medial leg and a diminished knee jerk.

What concept does this question test?

It tests Spine: disc prolapse in Orthopaedics. L5 weakness affects great toe extension and foot dorsiflexion, with sensory loss on the dorsum of the foot, whereas S1 compression causes weak plantar flexion, lateral foot numbness and loss of the ankle jerk.

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 Spine: disc prolapse?

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.