As this chick is the only one to hatch from a whole clutch that failed to break out of the eggs, it's very likely that it's going to always be disabled to some extent, whatever you do. You know all about the social problems of trying to raise a single chick, and if it lives you will end up with a bird that is not pefectly healthy and normal, so you couldn't breed from it, and there may be other underlying problems as well as lameness. I hope I don't sound too hard hearted when I say there is no point in raising any chick that isn't strong and apparently normal in every way, or in inflicting treatment which may distress the chick and probably not work. Nature may be telling you something if this hatch from an elderly cockerel was not successful, and if you want your flock to improve rather than to weaken, it should be survival of the fittest only, I feel.