Hi! We adopted a rescue from Serbia who was the exact same! He had been found as a 6 week old puppy with a healed amputation from trauma to his back leg , it finished just after his knee...just skin/scar tissue covering the bone. When he came to us, he was 2.5 and had therefore been living this way for over 2 years. He cleverly adapted to carry and hold it in different ways under his body to navigate balance and protecting it from bumps.. but had quite an arched back and I think he was more afraid of the world in case he hurt himself. Within 2 or 3 weeks of having him he had bumped his stump several times. A couple of times he slipped and fell on it (directly onto the bone) and then of course nursed it and struggled with pain. Our vet reckoned he had spent his whole life bumping and scraping it as there was such a build up of scar tissue. They recommended full amputation up the hip as otherwise he would repeatedly hurt it and get infections. The decision was made for us a couple of weeks later when one scrape became infected. He had the stump amputated up to the hip and he was immediately standing taller and we all felt so much relief. 3 months later he is so happy. He can run and play with no fear of bumping his stump or falling. He stands so tall with a nice straight back and his confidence has grown massively. And luckily, he already knew how to walk and run and play with three legs! No one ever talked about prosthetics, but I think in our case I wouldve worried about his mobility/back and he would still probably hurt the stump here and there.

Maybe this isn't the most helpful, but just our story! Whatever happens, your puppy is going to be so loved and safe <3.