History: 24 yo with knee swelling (be specific)
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Dense ossified mass arising from the posterior metaphysis of the distal femur in a 20-ish yo person.
Classic age, Classic location, Classic appearance for parosteal type
Parosteal arises from the outer fibrous periosteum so sometimes you can see a slight cleavage plain between the mass and the cortex (not here).
Actually low grade so better than the classic osteosarcoma and the rarer periosteal type