"Rolled Barrel" Before.
How to check your horse for this condition;
Horses barrels can be "rolled" in toward either leg.
Is the finger closer to one leg than the other? Is the difference more than 1/2 inch? If it is more than 1/2 inch, and by gently 'rocking' the withers, does the natural position of the horses chest remain closer to one leg? If so, your horse may have a "Rolled Barrel".
I have heard many reasons for this condition the most popular is by Farrier's usual comments are... "One leg is shorter than the other" and sometimes they want to put a shim, between the shoe and the hoof. Or if the horse is barefoot, they will want to try and have that hoof be 'taller'.