
Hi Guest, of course your vet is the best person to ask about this, but I wonder if it could be a patella luxation (slipping kneecap). At 5 months your puppy is growing very fast, and not all the bones grow at the same rate, tibia bones sometimes grow in a twisting pattern at this age and can cause the kneecap to top out of its groove. If this is the problem, it is probably only temporary until the puppy is nearly full height.
Good luck at the Vets. Why not join Champdogs (its free) and you can let us know what the vet has to say.
Dawn R.