I doubt we will ever find a definite answer but I'm wondering if anyone has seen this before? Because of Holly's heart issues we won't be sedating her to do X-rays but my vet is fairly certain she has Hip dysplasia (or possible a deformity in her hip that she was born with). When she is standing she always holds her hips at a funny angle. Kinda turned outwards. I never realized just how bad it was until my vet showed me how she should be standing. I was actually shocked I didn't notice just how much her differently she stands. As soon as my vet released her hips they went out again. She can't keep her hips in the proper position at all. Holly has always been very sensitive on her lower back (near her tail) and if you put light pressure she seems a little uncomfortable. In every day life it doesn't seem to bother her unless I try to groom her or mess with her back legs. She still runs and plays. My vet doesn't seem to think I should worry about it at the moment as there is little we can do to fix it.

Does this sound like something that can be caused from SM? Or does it sound more like Hip dysplasia?

She also can't sit still on any kind of slippery surface. Here is a video of her trying to sit on our kitchen floor. She is constantly sliding. It's more noticeable on slippery floors but she still moves a lot when she tried to sit on carpet. None of my other dogs "slide" around like she does on the slippery floor. Any ideas?