Haemodynamics: decompression sickness: practice question

A Pathology 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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Pathology · Haemodynamics: decompression sickness

Sample item

A commercial diver who ascended rapidly has acute joint pain. Years later he develops progressive hip pain, and radiographs show a subchondral lucent crescent in the femoral head. What is the mechanism of the chronic bone lesion?

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

The answer and the reasoning

C. Nitrogen bubbles obstructing the nutrient vessels of bone, causing ischaemic necrosis of the femoral head

On rapid decompression, dissolved nitrogen comes out of solution as bubbles that block small vessels. In the acute phase this causes the bends and chokes. Bone ischaemia may lead years later to avascular necrosis (dysbaric osteonecrosis), typically in the femoral head, humeral head and tibia.

Option by option

  • A. Immune complex deposition in the synovium causing erosive arthritis

    Immune complex synovitis produces erosive joint disease and not a subchondral crescent sign with a collapsing femoral head.

  • B. Chronic pyogenic infection seeded through the bloodstream during diving

    Pyogenic osteomyelitis presents with fever and inflammatory change, and is not linked to ascent from a dive.

  • C. Nitrogen bubbles obstructing the nutrient vessels of bone, causing ischaemic necrosis of the femoral head (correct)

    Correct. Gas bubbles in nutrient vessels cause avascular necrosis of bone.

  • D. Secondary hyperparathyroidism causing subchondral bone resorption

    Secondary hyperparathyroidism causes subperiosteal resorption in renal disease, which is not part of this history.

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 Pathology question

What is the answer to this Pathology question?

The best answer is C, Nitrogen bubbles obstructing the nutrient vessels of bone, causing ischaemic necrosis of the femoral head. On rapid decompression, dissolved nitrogen comes out of solution as bubbles that block small vessels.

Why is "Immune complex deposition in the synovium causing erosive arthritis" not the answer?

Immune complex synovitis produces erosive joint disease and not a subchondral crescent sign with a collapsing femoral head.

Why is "Chronic pyogenic infection seeded through the bloodstream during divi…" not the answer?

Pyogenic osteomyelitis presents with fever and inflammatory change, and is not linked to ascent from a dive.

Why is "Secondary hyperparathyroidism causing subchondral bone resorption" not the answer?

Secondary hyperparathyroidism causes subperiosteal resorption in renal disease, which is not part of this history.

What concept does this question test?

It tests Haemodynamics: decompression sickness in Pathology. In the acute phase this causes the bends and chokes. Bone ischaemia may lead years later to avascular necrosis (dysbaric osteonecrosis), typically in the femoral head, humeral head and tibia.

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 Haemodynamics: decompression sickness?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.