Oh My GOSH!! I have Rocco who has a bad leg like that!!! WOW You are the only one I know who has another dog like that! His back leg is straight but it does bend but it bends at the hip- it's his left back leg and when he runs, he tucks it up underneath him. He is 2 now and weighs around 15 pounds! I'm attaching a pic of him - its over a year old but if you look at his back leg its straight as an arrow. And I have 4 yorkies and he runs faster than all of them lol! I found him by chance in an on line ad when I was looking for estate auctions to go to. The breeder was trying to find him a home without having to put him down. He's incredible! The most loving dog and his favorite game is fetch! He loves to play that game and I think he would play it until he collapses so we have to watch that, lol. My vet took xrays when I first got him and said it was a birth defect and nothing could be done. When we first got him his back legs dragged behind him, he was pitiful looking. But after about 3 weeks of having a house to run around in he was up and running with the rest of the pack! Welcome to YT! I'm excited there's someone else here like my Rocco.