An eight years old boy presents with progressive swelling around the knee joint of two months duration following mild trauma . Local examination reveals an irregular bony swelling over the upper end of tibia, with raised local temperature and of variable consistency and defined margins. The most likely diagnosis is -

The clinical presentation in question can occur both in Ewing's sarcoma and osteosarcoma. History of trivial trauma Progressive swelling Raised local temperature Variable consistency ill defined margins. However, swelling is around the knee joint at upper end of tibia, which favours the diagnosis of osteosarcoma (metaphyseal lesion). Ewing's sarcoma usually occurs in the diaphysis of the bone (middle of the shaft).