The horse has three bones in the lower leg, with the cannon bone the largest and the main support. Equally important are the two small finger-sized splint bones that course down along the back of the cannon bone.
The splint bones taper down gradually, ending about two-thirds of the way down the cannon bone just above the fetlock joint. These small leg bones act as a brace, supporting the knee/hock and serve as an anchor for connective and supporting tissues.
In young horses, each long, slender splint bone is tied firmly against the cannon bone by strong, elastic tissue called the interosseous ligament. As the horse matures into his fifth and sixth year, the ligament calcifies, fusing the splint bones to the cannon bone.
Until the splint bones undergo this bony fusion and complete attachment, there is the possibility of getting a “splint.” Whenever there is too much stress/strain on the front legs of a young horse, the interosseous ligament may be stretched, torn or pulled. The body recognizes this as instability, and begins repair work which involves the formation of new bone that, in essence, prematurely fuses the splint bone to the cannon bone. This may cause heat, pain and a bony swelling ranging in size from a pea to a chicken egg on the insides of the cannon bone.
This bony enlargement is referred to as a “splint.” Splints may, or may not, result in lameness, and usually only affect the forelimbs.
Resting the horse allows the body to repair the instability and firmly reattach or calcify the splint bone to the cannon bone. Veterinarians may use many different methods to treat splints, but most would agree that the horse be rested and if possible placed on soft ground for at least 30 days. Veterinarians may also use medication to help reduce inflammation and prevent excessive bone growth. However, splints can heal without medication and treatment as well.
Persistent swelling, heat, pain and lameness is suspect for more troublesome involvement such as a fractured splint bone or accompanying soft-tissue injury. These horses may require veterinary guidance and intervention to attain the most favourable outcome.
Can splints be prevented? Yes, in a number of cases. Ageappropriate training in young horses is necessary to maintain a lifetime of soundness.
Per iods of rest are best included along the way. A heavy training regime for young two-year- old horses is often more than their legs can handle.
Growth spurts can temporarily render a young horse clumsy and even for the moment, conformationally incorrect until the whole body adjusts to the new changes. Work on hard concussive surfaces, and work at speed or in tight circles further compounds undue strain. Improper shoeing causing inappropriate hoof flight is best corrected immediately.
Malnutrition can also be a contributing factor. Conversely, a rich diet can play a role if it causes bones to develop too rapidly or the horse to gain more weight than their limbs can tolerate.