A splint is a periosteal new bone formation, also called periosteal exostosis, that originates from the cannon and/or the splint bones.
What causes it?
The periosteum is a special membrane that covers the outer surface of bones. It nourishes the bone, protects it and repairs the bone when it’s damaged. The cannon, splint bones and periosteum can get damaged and inflamed in different ways. External trauma, for example when a horse bumps its own leg with its foot during exercise, can cause a bruise in the periosteum or a crack in the splint bone. Excessive training or bad conformation can cause internal trauma, leading to splints.
The splint bones run from the carpus/hock down and end a few inches above the fetlock. They are attched to the cannon via a ligament. At the carpus/hock, the splint bones are part of the weightbearing system. Here they take weight, which is transmitted via the ligament down to the cannon. When excessive strain is put on this weightbearing system, the ligament of the splint bones can tear or become inflamed. Excessive training, especially involving high shock-absorbtion, can therefore lead to periosteal inflammation and splints. As the horse gets older, the ligament between the splint bones and the cannon ossifies, meaning it becomes bone as well. This makes the connection between the cannon and the splint bones stronger with age, which means that the splint bones can endure more which decreases the risk of splints developing.
When the periosteum becomes inflamed, the area will first swell up leaving a painful lump. Over time, the periosteum starts to make new bone through mineralisation of the swelling. When this happens, the lump becomes permanent. The periosteal new bone formation (splint) can irritate the surrounding soft tissue, such as the suspensory ligament that runs between them, and cause lameness depending on the size, shape and location of the splint. The suspensory ligament and the check-ligament are most often affected. If the splint is located very close to the carpus or hock, it may lead to arthritis in these joints.
The periosteum is very sensitive and will be painful in the acute stage, but bone itself is not sensitive. Once new bone formation has occurred and the inflammation is gone, the splint will not be painful or cause lameness as long as it doesn’t interfere with any tendons or ligaments. It can be hard to predict whether a splint is going to cause lameness, in which case we can only do our best to treat the splint and wait for the outcome.
A splint looks like a swelling in the area of the cannon or splint bones. In the acute phase it is warm and painful and may cause lameness. After a while the swelling can become a bit smaller and less painfull, because the swollen soft tissue is transformed into the less sensitive new bone. Lameness may persist if the splint is pressing on to tendons or ligaments. If a horse is not rested and treated appropriately, a splint may become progressively larger. Splints can occur on any leg, but occur most often in young sport horses on the inside of the front legs.
There are different ways of diagnosing a splint. In some cases the clinical signs may be enough. The splint can also be visualized using radiography or ultrasound. These techniques help determine:
- the location and size of the splint internally
- the amount of mineralization: is the swelling soft tissue inflammation or has new bone already started to form?
- whether there is a fracture
- whether the tendons have been damaged
The sooner a proper treatment plan is applied, the better the chances of limiting new bone formation. Your vet will determine the right protocol. This often consists of rest, frequent cooling and anti-inflammatories. Anti-inflammatories may be oral products, injectables or applied on the skin. Depending on the type and severity of the splint, a horse may be boxed for 4-6 weeks, combined with daily treatment protocols. If the horse is not rested properly, the damaged tissues can not recover, inflammation will continue and the splint will become larger. If some new bone formation occurs, leg protectors should be chosen so that they don’t rub or press on the splint too much during exercise. If a splint is too excessive it may be surgically removed, especially if the slint is interfering with the tendons. If one of the splint bones has been fractured, this will need to be addressed as well.
By using leg protectors during exercise, trauma to the cannon / splint bones can be prevented. However, leg protectors do not protect against the strains put on the tissues by excessive exercise. A training program should always be tailored to the individual to prevent issues such as splints, shin splints or other lamenesses. Always make sure you give your horse a good warming up and cooling down. Hose your horse’s legs down after exercise. It is also very important that the horse’s feet are trimmed correctly to prevent uneven strain on the tissues.
If you think your horse may have a splint, or if you have any questions about splints, please don’t hesitate to contact us.