By Dean Sinclair CJF, FE, DipWCF

Splint bones play an important role in supporting the horse’s lower limbs. But what are these evolutionary remnants of ancient toes, and what does it mean when a horse “pops a splint”?

Splint bones, which are the second and fourth metacarpal bones in the front limbs and the second and fourth metatarsal bones in the hind limbs, are thin, long bones that lie along both sides of the cannon bone (third metacarpal). The splint bones support the cannon bone and form the base of support for the knee (carpus) and hock (tarsus) joints. Splint bones are the remnants of the second and fourth toes that horses had before evolving to a single toe per limb. These bones are attached to the cannon bone by the interosseous ligament in young horses. As the horse matures, the splint bones eventually fuse to the cannon bone when the horse reaches five or six years old.

Splint boots protect the lower limbs from potential injury due to a horse’s own hooves striking the opposite limb. Photo: iStock/Vicvaz 

The terminology used to identify the condition can vary. A true splint refers to the tear or sprain of the interosseous ligament. The veterinary term for a popped splint in horses is exostosis, which is a bony growth on the splint bone. Interosseous desmitis is the inflammation of the ligament occurring between the splint bone and the cannon bone. Splints can be caused by several activities and conditions. Splints are more common on the medial side (inside) of the front limb but can occur on the hind as well.

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Causes

Trauma — A splint can result from a kick from another horse that lands on the splint bone and bruises or fractures the bone, as well as from limb interference on a front or hind limb (a horse striking its opposite leg). Limb interference is common with young Standardbred racehorses in training.

Nutrition — A nutritional imbalance or excessive feeding of nutrients such as calcium and phosphorous has been implicated in the development of splints.

Working on hard surfaces — Too much work on a hard surface can result in damage to the interosseous ligament. This damage can lead to a bone reaction (periostitis) on the surface of the splint bone resulting in a visible lump known as an exostosis.

Conformation — Poor conformation along with uneven weight-bearing can cause splints. Horses with toed-out or base-wide conformation are predisposed to medial (inside) splints, while horses with toed-in or base-narrow conformation are more likely to develop lateral splints (outside of the limb).

Treatment

Most cases respond well to rest. This can range from two weeks to three months depending on the severity of the injury and the horse’s recovery. Ice, cold-hosing, and supportive wraps can also aid in the recovery process. Your veterinarian may also prescribe anti-inflammatory medication. Regular and balanced trimming can prevent undue strain on ligaments and reduce the risk of splints. Return to work should be gradual and splint boots can be used to protect the horse’s lower limbs from injury.

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 Cold-hosing helps reduce inflammation and provides pain relief. Photo: AdobeStock/XtravaganT

Prevention

• Condition by increasing the workload slowly and gradually, and avoid working on hard or deep surfaces, especially with young horses.
• Maintain proper farrier care. Routine and correct trimming and shoeing can address confrontational faults that could predispose a horse to splints.
• Provide leg protection. Splint boots provide both support and protection against impact during exercise and turnout.

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More by Dean Sinclair

Main Photo: Splint on a three-year-old warmblood as a result of being worked too hard at a young age. Photo courtesy of Dean Sinclair.