An 11-year-old boy presents with shoulder pain after minor trauma. X-ray of the proximal humerus shows a centrally located radiolucent lesion in the metadiaphysis with a thin sclerotic rim, and a bony fragment lying dependent in the lower part of the cavity. This fragment sign indicates:

• A Pathological fracture through an aneurysmal bone cyst
• B Osteomyelitis with sequestrum formation
• C Fracture through a unicameral (simple) bone cyst ✓
• D Fibrous dysplasia with fracture

Explanation

The fallen fragment sign is pathognomonic of a pathological fracture through a unicameral bone cyst. Because the cyst contains fluid rather than solid tissue, a cortical fragment fractured off can fall by gravity to the dependent part of the cavity. In solid lesions such as ABC, fibrous dysplasia, or osteomyelitis with sequestrum, the fragment remains at the fracture site because there is no free fluid to allow it to sink.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.