Hi again NYC. When I got Butch from the shelter I notice that when I pinched his back legs, I could feel my fingers through the muscle. I was like, WTH?? After I had him about a month, he was running around playing and jumping up and down off the sofa and all of a sudden started screaming. Scared the holy crap out of me. I immediately took him to the vet, his knee had slipped out and would not stay in place. After xrays, they discovered that both knees where bad, in fact, the other one was worse than the newly injured one, but had just healed incorrectly, so we scheduled him for surgery. That was probably why he was at the shelter, they didn't want to pay to fix him. It's not cheap surgery, but if you can find a good vet that has done several surgeries, that would be your best bet. He has pins to keep his knees in place and afterwards, his back legs musceled right up. You might be able to find a vet that knows Chi's. Their little legs are so small, the vet needs to be experienced with Chi's.