This foal suffers from a flexural deformity of the distal interphalangeal, or coffin, joint.
Flexural deformities can be congenital or acquired. Most acquired deformities are considered part of the developmental orthopedic disease complex. It is thought that in fast-growing foals (determined by genetics and nutrition) the elongating growth of bones is greater than the associated muscle-tendon unit's ability to keep up.
In this case, functional shortening of the deep digital flexor tendon unit is applying excessive tension on the distal phalanx (coffin bone), resulting in palmar rotation of the entire hoof. In time in cases like this, the hoof takes on a club-foot shape. Some cases, if addressed early, will respond to nutritional management, therapeutic shoeing (toe extensions), analgesics, and physiotherapy. Others will require desmotomy of the accessory ligament (distal check) of the deep digital flexor tendon along with medical therapy. If not corrected early in its course, the deformity can worsen and lead to permanent changes of the regional soft tissues and bone remodeling.