Splints refer to swellings that develop on the splint or cannon bones, that are caused by repetitive strain during exercise or trauma at the site. When a splint first occurs, it presents as an inflammed and painful swelling. Over time, the swelling may ossify and form a bony prominence at the site. The splint bones, known as the second and fourth metacarpals, are narrow bones that run down the back of the horse's leg, on either side of the cannon bone.
Horses that develop splints on both front legs or both hind legs, found at the same locations, it is usually the result of concussion from working on too hard of a surface. When splints develop on one leg, it is most likely caused by trauma as a result of a direct kick from another horse, interference with the opposite foot, or some other trauma. Horses with splints may or may not show evidence of lameness.