Fallen fragment sign is characteristic of:

Ans. B. Simple bone cystSolitary Bone Cyst is also called a simple or unicameral bone cyst and affects children in the first and second decade. They arise in the metaphyses and are central or medullary. The proximal humerus and proximal femur are common sites. An SBC contains serous or serosanguinous fluid. They are seen as osteolytic, expansile lesions causing thinning of the cortex. Often with a fracture in the SBC, a "fallen-fragment" sign is commonly seen.