This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Fallen fragment sign is a feature of ? 
Select and explain. 
A. Simple bone cyst, B. Aneurysmal bone cyst, C. Giant cell tumor, D. Fibrous dysplasia
A: Simple bone cyst
Answer: A: Simple bone cyst 
Explanation: Ans. is 'a' i.e., Simple bone Simple bone cyst (Solitery/Unicameral bone cyst) Simple bone cyst occurs before the age of 20 years The most common site is proximal humerus (50%)followed by Proximal femur (25-30%). Radiological features are : - Concentric Metaphyseal Expansile lucent (lytic) Well defined border with sclerotic margin Fallen Fragment sign : - Coical fragment of pathological fracture settles in the most dependent poion. Hinged fragment sign : - Sometimes fractured fragment does not separate from adjacent coex.