Bite sign or snow cap sign is seen in which condition?

• A. Osteoarthritis
• B. Avascular necrosis
• C. Bone infarct
• D. Chondrosarcoma

Answer: (B)

Bite sign and snow cap sign are radiographic clues of avascular necrosis, the result of interrupted blood supply to a bone leading to death of bone tissue and potential collapse of the joint surface. On imaging, the bite sign appears as a small, notch-like indentation on the surface of the necrotic area, giving a bite-out appearance. The snow cap sign refers to a thin cap of reactive sclerosis over the necrotic zone, producing a cap-like contrast at the edge of the affected area. These features reflect subchondral involvement in AVN and help distinguish it from degenerative changes of osteoarthritis or from tumors, which show different patterns (OA with joint space narrowing and osteophytes; chondrosarcoma with destructive bone changes and matrix calcifications). In AVN, recognizing these signs supports earlier diagnosis before obvious joint collapse.