Splints

Splints is an ailment of the horse or pony, characterized by a hard, bony swelling, usually on the inside of a front leg, lying between the splint and cannon bone or on the splint bone itself. It may be "hot," meaning that it occurred recently and is still painful; or "cold," meaning that the splint has completely recovered and there is not longer any swelling or pain associated with it.

The splint bones, remnants of two of the five toes of prehistoric horses, run down either side of the cannon bone. They narrow as they go from the carpal joint down, and form a "button" at the bottom or their length, a few inches above the fetlock. Splint bones are attached to the cannon by the interosseous ligament, although they still have some mobility.

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Causes of splints

Direct trauma, such as from an interference injury or a kick from another horse, is a common causes of splints. The periosteum is damaged by the trauma, and the horse's body proceeds to lay down new bone in the injured area. Splints caused by trauma is usually a little lower down the leg than one caused by concussion. The splints may occur in a front leg or hind, in one leg or both. If in both legs, the splints are probably in different areas along the splint bone.

Concussion is another cause of splints. Concussive forces run up into the splint bones through the interosseous ligament. This tends to cause splints to occur in the narrowing of the splint bone, a few inches below the knee. Working a horse on hard surfaces increases the concussion received by the splint bone. Splints caused by concussion is usually found on both front legs, most commonly on the inside of the leg a few inches below the knee.

Overworking young or unfit horses at speed may cause splints. It takes several weeks for a bone to become denser and stronger, therefore, a horse that is overworked at speed before its bones have increased their density is more likely to develop splints.

Blind splints

Because the splint bone does have some mobility independent of the cannon bone, it can cause tension and strain on the periosteum of the splint bone where the interosseous ligament attaches. The horse will then lay down new bone and the area will become inflamed. This "blind splints" is named because the bony changes occur between the splint and cannon bones, rather than on the outside of the splint bone. "Blind splints" is difficult to diagnose.

Signs of splints

Splints usually cause mild lameness (a grade of 1-2 out of 5). The injured area is hot, painful, and inflamed with a small bony swelling. However, splints do not always cause lameness, especially once "cold".

Splints that occurs on the splint bone is usually longer and narrower than one that involves the cannon bone or the interosseous ligament.

"Blind splints" usually produce mild lameness that is difficult to pinpoint because there is not obvious swelling, pain, or bony changes related to the splint bone. When the horse is radiographed, it is possible to seen the calcification of the interosseous ligament. However, mature horses often have calcified interosseous ligaments naturally, that have occurred with age, so it can be difficult to diagnose blind splints in an adult horse.

The body will eventually absorb some of the bone it placed down in the splint, flattening out the splint over several weeks and possibly making it completely disappear. A splint involving the cannon is most likely to disappear than one involving the splint bone itself.

Treatment of splints

The horse should have a reduced workload for 1-3 weeks. If a trainer does not decrease the workload sufficiently, and the splint bone continues to receive concussion, the injury is likely to continue or worsen. Light exercise on soft ground is best for a horse with splints, as work can help encourage the needed bone growth to heal the splint. Those trainers concerned with the cosmetic appearance of their horse usually prefer to hand-walk twice daily and keep the animal stalled until the splint is resolved, eliminating the chance that the splint will accidentally be knocked during work and the swelling increased.

Several days of cold therapy, sweats, and NSAIDs can help a "hot" splint. NSAIDs can help reduce the inflammation and help the bone growth by doing so. However, none of these treatments are incredibly effective. The most important factor is time. Counter-irritants, which increase inflammation, only hinder the formation of bone and can actually prolong the healing process.

Surgical removal of the bone growth in large splints, performed by chiseling it away, usually does not produce satisfying results. Often, bone growth is stimulated by the surgery, and the size of the splint is increased. Only about a third of the time is surgery at all successful.

Prognosis for splints

Prognosis is excellent. The horse will be able to return to full work once the inflammation and pain ceases. Although the horse usually recovers quite quickly, horses with "blind splints" may take longer because the interosseous ligament must calcify completely. The calcification of the splint is usually a permanent blemish, though over a period of many years, the excess calcification may be reabsorbed to some degree, occasionally to the point that the splint is no longer visible.

Sources

King, Christine, BVSc, MACVSc, and Mansmann, Richard, VDM, PhD. "Equine Lameness." Equine Research, Inc. 1997. Pages 752-757.