Bucked shins are sometimes called 'shin splints,' which involve small stress fractures of the dorsal cannon bone, often seen in race training, and discussed elsewhere.
They narrow as they go from the carpal or tarsal joint down, and form a "button" at the bottom or their length, a few inches above the fetlock.
Splint bones are attached to the cannon by interosseous ligaments, providing some mobility in the young horse.
Direct trauma, such as from an interference injury or a kick from another horse, is a common causes of splints.
The periosteum is damaged by the trauma, and the horse's body lays down new bone in the injured area.
Working a horse on hard surfaces increases the concussion received by the interosseous ligament, which causes tearing.
The uneven loading of the limb in tight circles places excessive force on the medial splint, which can cause it to move excessively relative to the cannon bone, causing tears in the interosseous ligament and periosteal reaction.
Counter-irritants, which increase inflammation, only hinder the formation of bone and can actually prolong the healing process.
Surgery to remove the fractured end of the splint bone, particularly in the lower third, is typically successful.
However, surgical removal of the bone growth in large splints, performed by chiseling it away, usually does not produce satisfying results.