I forget the book name but its written by Brenda Aloff. It's textbook sized with a yellow cover.
It's something like illustrated dog body language maybe?
Anyway in the book it talks about an "i love you stretch"
Both a front leg stretch (similar to a play bow posture) and the hind leg stretch are friendly I like you behaviors. All of my dogs do this to me, to their favorite people at my work, and to each other.
This is not an indication of hip dysplastia. It's ny understanding that it hurts and I can't imagine a dog with hurting hips would purposely stretch themselves in a painful way.
"For the animal shall not be measured by man. In a world older and more complete than ours they move finished and complete, gifted with extensions of the senses we have lost or never attained, living by voices we shall never hear."