im quite sure this is what mine had in a hind foot although its common in front feet.
She only randomly had it in one and you wouldn't have known from the out side it was only after x raying it showed at 4 degrees negative with apperatly is quite a lot. she had wedges on for about 6 months and the farrier had to alter the way he shod her so now she looks like she has one more upright foot than the other but internaly they now match!
She now no longer needs the wedges.
She has several other larger issues which means she is now only a happy hacker but the foot issue is no longer a problem although we do feel it could have been the result of some of her other issues