I've read a lot about this disease and I am so sorry for what you have gone through. I'm new to the Yorkie world - my baby will be two next month. With my Bailey, I worried about the worst and hoped for the best - so far, we have dodged every yorkie scare - including Legg Perthes.
The only reason I am posting to this thread is that Bailey does the exact same thing when she pottys. She raises her rear right leg and puts all her weight on the left - she always pees at a tilt. Also, we have two steps from the deck to the patio and when going up those steps she slightly raises her right leg and launches off her left. (I wonder if this makes Bailey is left legged??
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I don't know if this is what your baby is doing - but I can tell you that my baby does it all the time.
Best wishes to you and Chloie!!!