The surgery was about three weeks ago. Our vet said she didn't see any more damage than what was done to the abdominal muscles and the punctured vein. He had quite a bit of blood loss and had to have a transfusion. She said she wasn't sure about the leg. When she did the x-ray there weren't any fractures. She said to just give it time to see what happens. He doesn't act like the leg bothers him at all. And he can feel when we touch it so I am confident it isn't paralysis. He hasn't really used it since the injury.
To a certain exent it probably is, and could do with physiotherapy...but then are you certain there wasn't some other damage? What did the vet say at the time? Also, how long ago was the surgery? If quite recent, then it could take some time to get back to normal.
On the other hand there may be something else going on as well. I think you really ought to dicuss this with your vet.
If it's simple, and general muscle atrophy from not being used -and that's that...then the vet should be able to recommend some physio that you could help your Yorkie with, to gradually strengthen the leg muscles. I would ask.