Splints in horses are hard lumps, which are actually bony enlargements found on the side of the horse’s leg between the knee and the fetlock joint, located where the splint bone runs down on either side of the cannon bone.
What are the splint bones?
The medial and lateral splint bones are the remains of the second and fourth digit of the horse’s five-toed prehistoric ancestor. Digits one and five disappeared during evolution, while two and four become splint bones, with the middle digit forming the weight-bearing cannon bone.
The upper two thirds of each splint bone is attached to the cannon bone by dense fibrous tissue called the interosseous ligament. The lower section flares away from the cannon bone slightly and is connected to the surrounding structures by soft tissue. The lower end of the splint bone has a small pea-like “button” which can be felt through the horse’s skin.
In most horses the interosseous ligament gradually changes with age as the splint bones fuse to the cannon bone at around three to four years. This process is normal and has no clinical signs.
What causes splints in horses?