A splint occurs when the horse gets an enlargement on the splint bone between the knee and the fetlock.

The use of splint boots can protect the inside of the leg if the horse’s action causes him to strike the area with the other foot.

Splints are enlargements that can occur along the length of a horse’s splint bones, two slender bones that begin under the horse's knee and continue down the cannon bone. These enlargements, often referred to as the horse “popping a splint” because the splint bone looks larger on the leg, indicate that the area has been inflamed.

Most splint problems are easily seen as a swelling along the course of the splint bone. The area will feel warmer than normal and be painful until this inflammation quiets down. During the healing process, the body’s reaction is to lay down more bone in an attempt to better stabilize the splint bone. This produces a permanent enlargement along the splint bone. In time, these bony enlargements can remodel and shrink to some degree, but they will always be present.

Inflammation can result from several sources: a kick or other trauma (the usual cause when the outside/lateral splint is involved), if the horse interferes and hits the splint area, or simply if a young horse is worked too hard and overstretches the ligament between the splint bone and the cannon bone.

Splints can also develop if you allow a young horse to get overweight. Mineral deficiencies, excesses or imbalances, especially of calcium and phosphorus, may also predispose a horse to splints. Medial or inside splints can develop if the cannon bones are offset to the outside, not perfectly lined up underneath the knee above them. Hooves that are not correctly balanced can result in uneven weight distribution and pressures along the leg, predisposing to many lameness problems, including splints.

Avoiding Splints

Make sure the feet are meticulously balanced. Don’t allow the horse to get overweight. Check that the diet contains adequate levels of calcium and phosphorus, and in the correct amounts (ideal of 1.2 to 2 times as much calcium as phosphorus). Avoid overworking young horses. Avoid speed work with young horses. Use splint boots if your horse has a tendency to wing his feet in rather than move them forward in a straight line.

Splint Complications
A blind splint is inflammation that occurs very high along the length of the splint bone and along its inner edge  (toward the cannon bone). In these cases, the swelling cannot usually be seen because it is located inside the connective tissue that stabilizes the knee joint. An experienced vet can detect the problem by carefully palpating in this area.

Splints that occur very high on the medial/inside splint bone carry a risk of also involving the knee joint in the inflammation because the head/top of this splint bone forms part of the knee joint. Large splints that involve the inner edge of the splint bones can also irritate and cause inflammation in the suspensory ligament.

When the stress on the splint bone is severe, or if a horse continues to work without letting the inflammation from a splint have a chance to quiet down, the splint bones may break. Fractured splint bones are more painful and produce a greater bone reaction, with a higher risk of involving the suspensory ligament.

Treating Splints
The most important part of treating splints is rest. The horse should be confined to a generously sized box stall or a small paddock until the inflammation has quieted down. This can take anywhere from two weeks to two months, and there’s no way to rush it along. Working the horse again too soon will only make things worse.

A Look at the Splint Bones

The splint bones are two very slender, splinter-like bones that begin under the horse’s knee and travel down the back of the cannon bone. At their top/knee end, splints have a knob-like head, with the bone beneath gradually tapering down until it is very slender at the end. In the young horse (under the age of about 5), the splint bones are attached to the cannon bone by ligamentous tissue. As the horse matures, the splints become fused to the cannon by bone. The suspensory ligament travels down the back of the cannon bone in the space between the two splint bones.

Having your veterinarian examine the leg is a good idea for several reasons. He/she will be able to assess if other structures may be involved, check for other problems that may be going on at the same time and give you some idea of how long it will probably take before the horse should be worked again.

For the first few days to a week, frequent cold-water hosing or ice packing of the leg will help tremendously in getting control of the inflammation. When cosmetic appearance is a major consideration, the vet may choose to inject a small amount of corticosteroid in an attempt to minimize how large the healed splint will be. However, this also slows healing, can make the horse comfortable by blocking inflammation (which could make you think it’s safe to work him again before it really is) and always carries some risk of infection.

After the acute inflammatory phase, mild counterirritants to encourage good blood supply are often used in hopes of improving healing. Although never scientifically proven, this is a popular practice and does no harm if used correctly. One of the most popular products is Splintex, from Horse Systems Inc., www.splintex-horsesysinc.com, $24.50/bottle. Consult with your vet before using a product like this, and anytime you think the healing process might not be going along like it should (e.g., if the leg stays hot and very swollen longer than a few days to a week, or if the pain, heat or swelling worsens).