Presentation
Child presenting with severe pain in arm following a minor fall.
Patient Data
Two x-rays of the right humerus demonstrate a lucency within the proximal diaphysis with slight expansion and a fracture. Lying medially within the cyst is a fragment of cortex.
The so-called fallen fragment sign is specific for a unicameral bone cyst, with a pathological fracture. Part of the thinned cortex 'falls' into the cyst, thus indicating that the lucency is A) fluid B) uni-loculated.
Distribution of unicameral bone cysts. Layout and distribution: Frank Gaillard 2012, Line drawing of skeleton: Patrick Lynch 2006, Creative Common NC-SA-BY
Case Discussion
Typical appearances of a large unicameral bone cyst with a pathological fracture and fallen fragment sign.
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