A-12-year-old boy presents with chronic knee pain for 2 years. Knee X-ray is shown. Probable diagnosis:

Ans: (b) OsteosarcomaRef: Fundamentals of Orthopedics by Mohindra and Jain, 2nd edition, Jay pee Publishers, Page 325 and Figs. 11.34-35X-ray shows periosteal reaction around distal femur.Going by the site (distal femur) and age group (2nd decade), answer is osteosarcoma > chronic osteomyelitis (seen in relatively older age group).In osteosarcoma periosteal reaction (bone formation under the periosteum) may take the form of sunray appearance (bone formation along sharpey's fibers) or codman's triangle.The X-ray in question seems to depict sun ray appearance.X-ray Appearance in OsteosarcomaThe X-ray appearances are variable.Hazy osteolytic areas may alternate with unusually dense osteoblastic areas.The endosteal margin is poorly defined.Often the cortex is breached and the tumour extends into the adjacent tissues; when this happens, streaks of new bone appear, radiating outwards from the cortex - the so-called 'sunburst' effect.Where the tumour emerges from the cortex, reactive new bone forms at the angles of periosteal elevation (Codman's triangle).While both the sunburst appearance and Codman's triangle are typical of osteosarcoma, they may occasionally be seen in other rapidly growing tumours.