Splint

On each side of the cannon bone is a small bone known as the splint bone. The small splint bones are thin and taper to become a small knob about two-thirds of the way down the cannon bone

A ligament, located between the cannon bone and the splint bones, is quite elastic in young horses. As the horse ages, the ligament ossifies; that is, the ligament is replaced by bone and the three bones fuse. During ossification, there may be inflammation and pain. Jumping, running and working a horse during this time produces further irritation.

Splints usually occur in horses 2 to 5 years old. Most often it is the forelimbs that are affected. They rarely occur in the hind legs. In older horses, the splint bones are fused solidly to the cannon bone. The majority of splint problems occur on the inside splint bone because it has a flat surface next to the knee. The outer splint bone has a more slanted surface. When the weight is transmitted to these bones, the inside splint bone probably bears more weight and therefore the ligament on that side subjected to more stress than the outer ligament.

Signs of splints
Lameness due to splints is most common in 2-year-old horses undergoing training. The lameness is most obvious while the horse is trotting or working or soon thereafter. It may come and go or be present continuously for as long as a year.A large swelling or a number of smaller swellings due to ossification may occur along the length of the splint bones. After the ligament has ossified, the swelling and soreness usually disappears.

Treatment
The horse should be rested and placed on soft ground for at least 30 days. The vet may use medications to help reduce inflammation and help prevent excessive bone growth, but it is true that splint bone disease may heal without medication and treatment. The outlook is good for most horses except those in which the bony growth is large and interferes with the knee joint. Sometimes surgery may be helpful in these difficult conditions.