I have talked about this issue since the early 1990's. I presented a Powerpoint lecture on Retracted Soles at the 2012 International Hoofcare Summit in Cincinnati, Ohio. The article from that lecture was published in the September/October 2012 issue of the American Farriers Journal. Link to article.
Retracted soles are a condition that several equine professionals have seen, but has yet been defined or described in any equine medical dictionary. There are only a few published or electronic references to retracted soles that can be found and only one source for pictures and radiographs.
Medically, retraction or retracted is the act of drawing back, or a condition of being drawn back. The soles of a horse with retracted soles are drawing back or rather up and away from the ground. The soles appear to be being sucked up into the hoof. During this process the soles become overly thin causing the horse to be very sensitive to the slightest sole pressure. Therefore, a good definition for retracted soles may be soles that are thin and abnormally cupped. The appearance cannot be mistaken for any other sole issue. Instead of having a nice sole concavity, the sole appears to drop off from the white line. Retracted soles that go unnoticed by a farrier during the trimming process can result in overly trimming the hoof wall thus causing the horse to become extremely painful due to sole pressure.