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?
A true splint occurs when the interosseous ligament becomes damaged, leading to soft tissue inflammation and lameness with heat, pain and swelling in the area between the splint bone and cannon bones.As the acute inflammation settles and healing proceeds, new bone is laid down in this area, eventually forming a hard, non-painful lump, the size of which depends on the degree of original damage.This is the splint, which will reduce in size over time, but is unlikely to disappear. The new bone stabilises the source of irritation by forming a bridge between the digits.
These splints occur most typically on the inside of the forelimb, or on the outside of the hind limb in young, immature horses in work.
False splints in horses
False splints occur as a result of direct external trauma to the splint bone itself, such as the striking of the inside forelimb with the opposite leg, or kicks to the outside splint bone during field trauma or injuries. A bony lump forms where there has been bruising and damage to the periosteum covering the bone.
Fractures of the splint bone, which are most common in young horses, can also lead to the formation of a splint. Kicks and infected wounds can also cause fractures along the splint bone. There are also some fractures of the distal or thinner lower end of the splint bone that are associated with excess bending of the fetlock, due to weakening of the suspensory ligament caused by desmitis.
Diagnosis and treatment of splints in horses
The diagnosis of a simple splint is usually achieved on clinical signs, but your vet may wish to X-ray, or much less commonly, use other imaging techniques, if complications, such as a fracture, are suspected.
A fractured splint should be suspected, if a horse has an open wound, often from a kick injury, on the side of the cannon bone , which is slow to heal.
In the majority of cases the main forms of treatment are rest and anti-inflammatory therapy, with hydrotherapy used in some chronic cases. Prolonged peroids of rest may be needed.
Once the splint has finished forming, most horses are able to return to work and suffer no on-going problems from a splint, although they can be unsightly and may be considered a significant blemish, particularly in show horses. If the swelling is reduced surgically, there is a high chance of recurrence in operated horses.
The main concern associated with fully formed splints is cosmetic, although a splint positioned close to the knee joints could lead to carpal arthritis or it has the potential to interfere with the soft tissues, although this would be unusual.
The usual complication with almost any splint is the amount of time off required, which can stretch into months and be particularly problematic in older competition horses.
With this in mind, it is worth following these simple steps to lessen the risk of a splint forming in the first place:
- Exercise: don’t do too much too soon, especially on hard ground
- Maintain proper foot trimming and shoeing
- Use exercise boots or bandages to reduce interference injuries
- Manage horses kept together to minimise kick injuries, as much as possible