A 14-year-old presents with a 3-month history of bone pain around the knee. X-ray shows a destructive lesion in the distal femoral metaphysis with periosteal elevation forming a Codman's triangle and a 'sunburst' spiculation pattern. Serum alkaline phosphatase is markedly elevated. The most likely diagnosis is:
- A Osteosarcoma ✓
- B Ewing's sarcoma
- C Giant cell tumour
- D Chondrosarcoma
Correct answer: A. Osteosarcoma
Explanation
Osteosarcoma is the most common primary malignant bone tumour in adolescents and typically occurs in the metaphysis of long bones around the knee (distal femur most common, followed by proximal tibia). The sunburst pattern of periosteal new bone formation and Codman's triangle (elevation of periosteum at tumour margin) are classic radiological signs. Elevated alkaline phosphatase reflects osteoblastic activity. Ewing's sarcoma has an 'onion-skin' periosteal pattern and is usually diaphyseal.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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