They act like splints on both sides of the cannon bone. When a horse strains or damages the connection between the splint bone and the cannon bone, swelling and inflammation of the splint is called a 'true splint' and is commonly seen with mild to moderate lameness, heat, swelling and tenderness. Sometimes the damage to the ligament is not as severe, and the swelling occurs between the splint bone and the cannon, so that is much harder to see or feel. OK, as to your question, there are a number of causes for splints and factors that contribute to them. Conformation abnormalities that increase the stress on either the inside or outside of the leg can predispose to splints.
Splints are more of a condition in young, growing horses.
Imbalance in nutrition or overfeeding can also lead to splints. It occurs more during periods of rapid growth because the bones are not strong yet, and the horse's weight on those soft bones is increasing. I'm not saying Clyde did anything wrong. But certain horses tend to have uneven growth to their feet, and need constant attention to make the hoof land level. I can't tell you exactly what caused your horse to pop a splint, but think about the causes I've mentioned and see if they apply.