A 10-year-old child presented with a swelling and mild pain around knee joint along with muscle wasting. X ray: there was a lesion arising from epiphysis. Biopsy was done from the lesion and HPE examination was done. What is the diagnosis?

The age being less than 18yrs (age of skeletal fusion), epiphyseal lesion with internal speckled calcification, chicken wire calcification and giant cells suggest chondroblastoma. Chondrosarcoma is seen in adults arising from flat bones like pelvis. It shows speckled or popcorn or arc and ring calcification. Osteosarcoma has diffuse calcification, arises from metaphysis and is usually seen in 2nd decade. Osteoblastoma usually arises from posterior column if spine.