Does it eat will it drink? Are you shure its leg was broken? I've seen lots of turtles missing one or more feet and parts of legs that were chewed off. Somehow they heal and the animal survives. If Its been broken for so long there is not much that be done other than break it again and set it if its not right. Is the bone sticking out the skin? does it look infected? If its just not using it while it heals keep it alone and quiet and if its eating it should be OK. If its not eating or drinking for a long time or it is showing some other distress you should bring it to a reptile vet or give it to someone else don't just let it languish in a corner till it dies. The unfortunate reality of many of our reptile friends.