Conditions of the splint bone are very common, with smaller splints considered perfectly acceptable in the older performance horse. But what exactly are splints and when are they a problem? To answer this we need to understand how the horse’s leg evolved.

Originally the horse’s ancestor had 5 toes, but during evolution the horse became weight bearing on just the middle digit of each limb (the cannon bone). Digits 1 and 5 disappeared, with 2 and 4 reducing in size to form the functionally redundant medial and lateral splint bones.

The upper 2/3rds of each splint bone is attached to the cannon bone by dense fibrous tissue called the interosseous ligament. The lower section flares away from the cannon bone slightly and is connected to the surrounding structures by soft tissue. The lower end of the splint bone has a small pea-like “button” which can be felt through the horse’s skin.

In most horses the interosseous ligament gradually disappears with age as the splint bones fuse to the cannon bone. This process is normal and has no clinical signs.

True splints

These occur when the interosseous ligament becomes damaged, leading to soft tissue inflammation and lameness with heat, pain and swelling in the area between the splint bone and cannon bones.

As the acute inflammation settles and healing proceeds, new bone is laid down in this area, eventually forming a hard, non-painful lump, the size of which depends on the degree of original damage. This is the splint, which will reduce in size over time, but is unlikely to disappear. The new bone stabilises the source of irritation by forming a bridge between the digits.

These splints occur most typically on the inside of the forelimb, or on the outside of the hind limb in young, immature horses in work. Poor conformation, mineral imbalance in the diet, excessive weight of horse or rider, work on hard and uneven going, and unbalanced hooves can all lead to splints forming.

False splints

These occur as a result of direct external trauma to the splint bone itself, such as the striking of the inside forelimb with the opposite leg, or kicks to the outside splint bone during field scuffles. A bony lump forms where there has been bruising and damage to the periosteum covering the bone.

Fractures of the splint bone, which are most common in national hunt horses and young eventers, can also lead to the formation of a splint. Kicks and infected wounds can also cause fractures along the splint bone.

Diagnosis and treatment of splints in horses

The diagnosis of a simple splint is usually quite straightforward, but your vet may want to use additional techniques, such as X-raying, ultrasound or scintigraphy if complications, such as a fracture, are suspected.

The treatment of true splints tends to be governed by personal preference, and there are no proven treatment regimes that will work quickly and effectively. In most acute cases rest and anti-inflammatory therapy are the main forms of treatment, with hydrotherapy and counter-irritation therapy used in some chronic cases.

While the main concern associated with fully formed splints is cosmetic, a splint positioned close to the knee joint could lead to carpal arthritis, while any splint is likely to require the horse to have time off. With this in mind, it is worth following these simple steps to lessen the risk of a splint forming in the first place:

  • Diet – feed according to work done and check the mineral balance
  • Exercise – don’t do too much too soon, especially on hard ground
  • Maintain proper foot trimming and shoeing
  • Use exercise boots or bandages to avoid interference injuries

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