A dropped sole is a 'flat foot'. It can be caused by breeding but this shoe was more likely to have been made for a horse that worked in wet and muddy conditions and the condition, if neglected can cause severe pain. The 'coffin' bone in the horses hoof becomes flat so excessive pressure is placed on the softer underside of the foot. Laminitis can also develop. Heart bar shoes can be used to alleviate the condition.