Well it's hard to see him dragging his body without seeing a video. I think his legs look ok. In the one picture I thought they looked a little weird, but they look ok in the others so maybe it is just the angle. If he does have the start of MBD, you could easily correct that with proper calcium and uvb if he has been deprived that so far. He is still quite young and if there is any damage, it should be minimal because of his age. Do you know anything about his history?