A 17-year-old girl presents with night pain and swelling near her knee. An X-ray shows periosteal lifting. Which of the following findings is likely to be seen on the X-ray?

• A. Onion skin periosteal reaction
• B. Fallen leaf sign
• C. Ground glass appearance
• D. Codman's triangle

Answer: (D)

The presence of night pain and swelling near the knee, along with X-ray findings of periosteal lifting, suggests a potential underlying process like an osteosarcoma or other aggressive bone lesions. In this context, the finding of Codman's triangle on the X-ray is particularly relevant.

Codman's triangle occurs when there is an elevation of the periosteum due to aggressive processes such as tumors or infections. It is characterized by the triangular area of new bone formation that forms at the periphery of the lesion where the periosteum has lifted away from the underlying bone. This is often associated with osteosarcoma, which is one of the most common bone cancers in adolescents and can manifest in this age group.

Other findings mentioned, such as the onion skin periosteal reaction, typically represent a more gradual and less aggressive process like Ewing's sarcoma or reactive periostitis. The fallen leaf sign is associated with specific conditions such as a unossified bone cyst, and the ground glass appearance often relates to fibrous dysplasia. These conditions would not typically present with the same acute symptoms and aggressive features as suggested by the presented case.

In summary, Codman's triangle is indicative of an aggressive bone pathology with periosteal reaction, aligning