It could be genetic but I've had that happen to adult birds... Think it's a few slipped tendons out of place, since they were fine before. It doesn't seem to be painful or a problem, but trying to fix it could be. I've tried in vain, with endless splinting, to get a chooks' main leg tendon back into place... Gave up, the tendon would go back but not stay when unsplinted, he grew up with a leg sticking out to the side. :S