Question:medium
The fallen fragment sign is characteristic of:
The fallen fragment sign is characteristic of:
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A chip sinks through clear fluid - a single-cavity unicameral cyst.
Updated On: Jun 24, 2026
- Simple bone cyst
- Osteosarcoma
- Adamantinoma
- Aneurysmal bone cyst
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The Correct Option is A
Solution and Explanation
Step 1: Think physically about what the sign requires: a detached bone fragment must be able to sink under gravity, which is only possible inside a cavity filled with thin fluid and no solid tumour matrix or thick septa.
Step 2: A simple (unicameral) bone cyst is a single fluid-filled cavity. When it fractures, a chip of its thin wall breaks off and gravitates to the most dependent part of the cyst, producing the fallen fragment sign. This appearance is regarded as diagnostic of a simple bone cyst.
Step 3: Rule out the rest: osteosarcoma and adamantinoma are solid lesions through which nothing can fall; an aneurysmal bone cyst is multiloculated with blood-fluid levels rather than one open fluid space, so a fragment cannot freely descend. The classic teaching ties the sign to the simple bone cyst.
\[\boxed{\text{Simple bone cyst}}\]
Step 2: A simple (unicameral) bone cyst is a single fluid-filled cavity. When it fractures, a chip of its thin wall breaks off and gravitates to the most dependent part of the cyst, producing the fallen fragment sign. This appearance is regarded as diagnostic of a simple bone cyst.
Step 3: Rule out the rest: osteosarcoma and adamantinoma are solid lesions through which nothing can fall; an aneurysmal bone cyst is multiloculated with blood-fluid levels rather than one open fluid space, so a fragment cannot freely descend. The classic teaching ties the sign to the simple bone cyst.
\[\boxed{\text{Simple bone cyst}}\]
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