I would not amputate that leg unless ALL options have been considered. If that ortho vet you are using is not a Board Certified Vet Surgeon, I suggest going to one for a second opinion.
It is true that splinting will not repair these fractures.
It only works in 5% of cases!! I wish vets would tell people that before they put these pups and the owners through it. We did get a pup that had been through it and the surgeon we use was able to save her leg. She did require bone grafting. We also had another pup in another state who sadly lost his leg in the end. But we tried everything first!
These bones are very tiny so there is not as much blood flow, hence the healing issues; but they can often be saved.
You can find a board certified surgeon at this link:
www.acvs.org
Feel free to message me if you have any questions. I have dealt with many orthopedic cases and personally have only lost one limb and that was because the pup had sciatic nerve damage and had chewed his foot off before he came to me.