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 no longer any swelling or pain associated with it. Bucked shins are sometimes called 'shin splints,' which involve small stress fractures of the dorsal cannon bone, often seen in race training, and discussed elsewhere.

The splint bones, (metacarpal or metatarsal II and IV), which are 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 or tarsal 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, providing some mobility in the young horse. As the horse ages, the interosseous ligament is typically replaced by bone. In some older horses, the cannon and splint bones may become completely fused.

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 lays down new bone in the injured area. Splints caused by trauma are more commonly seen lower down the leg than ones caused by strain. The splints may occur in a front leg or hind, in one leg or both. Severe enough trauma can fracture the splint bone. If minimally displaced, and in the lower portion, some heal well. Others may need surgical removal of a portion of the damaged splint bone.

Concussion is another cause of splints. Concussive forces run from the carpus or tarsus into the splint bones. Working a horse on hard surfaces increases the concussion received by the interosseous ligament, which causes tearing. Splints caused by concussion are 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 or in tight circles may cause splints. The uneven loading of the limb in tight circles places excessive force on the medial splint, which can cause it to move excessively relative to the cannon bone, causing tears in the interosseous ligament and periosteal reaction.

Bench-kneed conformation causes excess loading of the medial splint bone, which can lead to splints.

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