Fractures and dislocations: lag screw technique: 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 · Fractures and dislocations: lag screw technique

Sample item

A surgeon fixes an oblique fracture of the lateral malleolus with an interfragmentary lag screw. What is essential for the screw to compress the fracture?

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

The answer and the reasoning

B. The threads grip only the far fragment, and the near cortex is overdrilled as a gliding hole

A lag screw compresses because the head pulls the near fragment toward the far fragment. This requires the threads to purchase only in the far fragment, with the near fragment drilled larger (gliding hole) or a partially threaded screw. A partially threaded screw, or a fully threaded screw in an overdrilled near cortex, achieves the same effect.

Option by option

  • A. A fully threaded screw is placed through a tight hole in the near cortex

    A tight near-cortex hole with threads engaging it would stop the near fragment from sliding towards the far one.

  • B. The threads grip only the far fragment, and the near cortex is overdrilled as a gliding hole (correct)

    Correct. Threads in the far fragment alone, with a gliding hole in the near one, produce interfragmentary compression.

  • C. The screw must run parallel to the fracture line

    A screw parallel to the fracture line gives no compression across the fracture.

  • D. The threads must engage both fragments

    If the threads grip both fragments they hold the gap open and prevent compression.

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, The threads grip only the far fragment, and the near cortex is overdrilled as a gliding hole. A lag screw compresses because the head pulls the near fragment toward the far fragment.

Why is "A fully threaded screw is placed through a tight hole in the near cor…" not the answer?

A tight near-cortex hole with threads engaging it would stop the near fragment from sliding towards the far one.

Why is "The screw must run parallel to the fracture line" not the answer?

A screw parallel to the fracture line gives no compression across the fracture.

Why is "The threads must engage both fragments" not the answer?

If the threads grip both fragments they hold the gap open and prevent compression.

What concept does this question test?

It tests Fractures and dislocations: lag screw technique in Orthopaedics. This requires the threads to purchase only in the far fragment, with the near fragment drilled larger (gliding hole) or a partially threaded screw. A partially threaded screw, or a fully threaded screw in an overdrilled near cortex, achieves the same effect.

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 Fractures and dislocations: lag screw technique?

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.