What is the most likely diagnosis for a 17-year-old girl with night pain, swelling near the knee, and Codman's triangle on X-ray?

• A. Osteoid Osteoma
• B. Enchondroma
• C. Multiple Myeloma
• D. Osteosarcoma

Answer: (D)

The symptoms and findings described for the 17-year-old girl align closely with a diagnosis of osteosarcoma. Osteosarcoma is a primary malignant bone tumor typically occurring in adolescents and young adults, often around the knee joint, which correlates with the patient's age and the location of the swelling.

Night pain is a common symptom associated with osteosarcoma, as the tumor can cause significant discomfort, which tends to be more pronounced at night. Furthermore, the presence of swelling near the knee suggests an aggressive process, which is characteristic of osteosarcoma.

Codman's triangle, visible on an X-ray, is a classic radiological sign associated with osteosarcoma. It appears as a triangular area of new bone formation that occurs at the periphery of a bone lesion. The presence of this finding, combined with the clinical symptoms of night pain and swelling, strongly supports the diagnosis of osteosarcoma.

In summary, the combination of the patient's age, the location of symptoms, night pain, swelling, and the identification of Codman's triangle on imaging work together to establish osteosarcoma as the most likely diagnosis in this case.