Those are all general tests, and in reality, might be used to rule out almost anything, not osteosarcoma. From what you have described, this still sounds like Osgood Schlatters disease to me. As I'm sure you know, Osgood Schlatters disease is a benign irritation of the attachment site for the patella tendon. It occurs in children because that area is made of uncalcified cartilage and is a result of overuse. Osgood Schlatters is part of a group of common overuse injuries in children known as osteochondroses.