Unicameral bone cyst: Fallen fragment sign

(A) AP humerus – Observe the large metaphyseal unicameral bone cyst with a cortical fracture (arrow). The fractured fragment is demonstrated in the most caudal portion of the radiolucent defect, representing a fallen fragment sign (arrowhead), which is also known as a "fallen leaf" sign.
(B) AP – Observe the radiolucent unicameral bone cyst with soap-bubbled matrix located centrally within the proximal metaphysis of the humerus. There is a small cortical fracture (arrow) with a fallen fragment sign within the cystic radiolucencies (arrowhead). Approximately 10 percent of patients with unicameral bone cyst present with a fallen fragment sign.