Is the bone showing through the skin? If so dart the buck and get him sleeping so you can get a good look. Amputate or dress the wound depending on how severe. If the leg appears to be a minor interior break, I have just let them go and only gave banamine (asprin for deer) for a couple days to help with pain and swelling. I have found that broken legs tend to heal very fast on whitetails, even with no splints.