Fallen fragment sign
MSKRadiograph / CT
A small bone fragment lies dependently within a lucent bone lesion, having fallen to the most dependent part of the cavity.
What it means
A fluid-filled simple (unicameral) bone cyst that has sustained a pathological fracture.
Mechanism
A cortical fragment from a fracture through the thin wall of a fluid-filled cyst sinks to the dependent portion of the cavity.
Associated conditions
- Simple (unicameral) bone cyst
- Pathological fracture
- Proximal humerus lesions
- Proximal femur lesions
Pearls
- The sign confirms the lesion is fluid-filled rather than solid, favouring a simple bone cyst.
- It helps distinguish a simple bone cyst from an aneurysmal bone cyst or solid tumour.
References
- Radiopaedia: Fallen fragment sign
For educational use only. This dictionary is a study aid and reference, not a diagnostic tool, and must not be used to guide clinical decisions or patient care. Imaging appearances vary; always correlate with the full clinical picture and confirm with a qualified radiologist.