Question

Fallen fragment sign is seen in -

• A. Simple bone cyst
• B. Osteosarcoma
• C. Adamantinoma
• D. Aneurysmal bone cyst

Hint:

Which hollow, fluid-filled lesion lets a broken fragment drop freely inside it?

Answer 1

The Correct Option is A

Step 1: The fallen fragment sign describes a small bone fracture fragment that drops and rests dependently within a fluid-filled cystic bone lesion. It is best seen on a radiograph when the patient changes position and the fragment settles at the dependent part of the cavity.
Step 2: This sign is considered pathognomonic for a simple (unicameral) bone cyst that has sustained a pathological fracture. Because a simple bone cyst is hollow and fluid-filled, a broken cortical fragment can fall freely into the cavity - hence option a is correct.
Step 3: Osteosarcoma and adamantinoma are solid tumours, so a fragment cannot fall through them. An aneurysmal bone cyst is multiloculated and blood-filled with septa, so a fragment cannot drop freely; this is why options b, c and d are wrong.
Step 4: Although rare reports describe the sign in other cystic lesions such as eosinophilic granuloma, for examination purposes the fallen fragment sign points to a simple bone cyst.