The best solution is taking it to a vet and he will be able to help you thoroughly. Accepting answers from blurtit may be incorrect and may even worsen your puppy's condition.
Your other question was how to tell if it's broken and you wouldn't want to assume a sprain or anything else and be wrong. You would need to see the vet to determine the problem and what needs to be done for your pup. You don't want to do the absolute wrong thing for your baby by not consulting a doctor first and make things worse. They will know more once they are able to examine your pup and talk to you about everything. Give them a call and/or set up an exam before you do anything other than restrict activity (kennel rest) and then the vet will let you know what you can do from there. Good Luck.
You just have to massage it in a few secs. Then let the puppy go. It will be okay in a few minutes,