OP, we had exactly this situation. At 10 weeks' old our puppy had a freak accident slipping off the sofa (whilst crawling over us) and managed to fracture his hind leg. It was a very complex twisted fracture as well. I have no idea how it happened! One minute he was on top of us and the next he was screaming and jumping on 3 legs 😭He was only a tiny baby. It was so so awful taking him to the hospital
The vet said they cannot operate on a puppy so small because the bone will completely shatter if they tried to put metal screws in there. BUT luckily he sent the X-rays to Davies Veterinary Specialist clinic (in Hitchin) and their specialist orthopaedic team agreed to operate. I really cannot recommend them enough if you are anywhere near them. They are true miracle workers. Not only was the surgery a success, but he recovered very quickly and now no one could ever tell that he had ever fractured his leg. He is sooo fast and agile, loves racing big dogs and agility.
If you are anywhere near them, I would ask your vet for a referral just to get a second opinion. They are specialists in orthopaedics.
As for recovery- our dog refused to stay in the carte. He would cry and jump on his hind legs to get out, which defeated the purpose. So we just carried him everywhere and kept him on a short leash in the house to prevent him running.
It took about 6-8 weeks to fully heal, but puppies' bones do heal well and the fractured bones once healed will actually be much stronger.
He is now 16 months and the friendliest most loving dog, so the horrible experience and slightly delayed socialisation clearly didn't do any lasting damage.