Musculoskeletal imaging: double-line sign: practice question

A Radiology 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.

Try it

Radiology · Musculoskeletal imaging: double-line sign

Sample item

A T2-weighted MRI of the hip in a 38-year-old man on long-term steroids shows a serpiginous band at the margin of a segment of subchondral marrow, with an inner high-signal line and an outer low-signal line. Which condition does this sign indicate?

AOsteoarthritis of the hipBSeptic arthritis of the hipCOsteonecrosis of the femoral headDSubchondral insufficiency fracture

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

The answer and the reasoning

C. Osteonecrosis of the femoral head

The double-line sign is specific for osteonecrosis. The inner bright line is vascular granulation tissue and the outer dark line is a sclerotic reactive rim around the necrotic segment.

Option by option

A. Osteoarthritis of the hip
Osteoarthritis shows joint-space narrowing, osteophytes and subchondral cysts, not a serpiginous double band.
B. Septic arthritis of the hip
Septic arthritis shows a joint effusion with synovial enhancement and marrow oedema, without this band.
C. Osteonecrosis of the femoral head (correct)
Correct. An inner bright and outer dark line around necrotic marrow is the double-line sign of osteonecrosis.
D. Subchondral insufficiency fracture
A subchondral insufficiency fracture shows a single low-signal line with surrounding marrow oedema.

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.

Questions about this Radiology question

What is the answer to this Radiology question?

The best answer is C, Osteonecrosis of the femoral head. The double-line sign is specific for osteonecrosis.

Why is "Osteoarthritis of the hip" not the answer?

Osteoarthritis shows joint-space narrowing, osteophytes and subchondral cysts, not a serpiginous double band.

Why is "Septic arthritis of the hip" not the answer?

Septic arthritis shows a joint effusion with synovial enhancement and marrow oedema, without this band.

Why is "Subchondral insufficiency fracture" not the answer?

A subchondral insufficiency fracture shows a single low-signal line with surrounding marrow oedema.

What concept does this question test?

It tests Musculoskeletal imaging: double-line sign in Radiology. The inner bright line is vascular granulation tissue and the outer dark line is a sclerotic reactive rim around the necrotic segment.

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 Musculoskeletal imaging: double-line sign?

Learn signs with the image, and the disease they point to. Then use the flashcards and the other Radiology 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.