i had a puppy bought to me by a bloke and it had a dodgy front leg and it kept buckling forward found out the whole litter of about 7 had the same problem a couple had the same problem with all 4 legs
its where they never got enough calcium or milk from the mother probably where she was taken away too early when i took it to the vet, said its leg will never heal properly even after an op and it would never be able to run it, said it didnt seem to be in any pain so you might aswell let it be bloke come back for the dog and took it back anyway dont know what happended to the litter