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Too much, too young: Splints

© Sally White

Many years ago, I used to run a lot. I pounded the streets for seven or eight miles at a time, convinced I was getting myself fit, but in fact I was slowly but surely jarring and bruising my shin bones until in the end they started, literally, cracking up with a stress fracture. It was sheer agony, and ironically ended up in my taking so much time off exercising that I was as unfit as I had been to begin with.

Why am I telling you this? Because something very similar can happen to young horses. The effect of long, hard training on bones which are still forming is similar to miles of jogging on hard surfaces, and young legs just can't cope. Splints, as they are known, are the most common cause of lameness in young horses, and usually happen when the horse begins serious work.

What are splints?

The problem can arise on both forelimbs and hindlimbs. The splint bones flank each side of the cannon bones, and are long, thin, slightly curved bones which taper down towards the fetlock and end a little way above. They are attached to the cannon bones by very flexible ligaments in young horses, but as the horse grows older become unified with the bone.

Splints form when the tissue which lines the splint bones becomes damaged and inflamed. The body reacts by producing new bone to compensate, usually rougher and less dense than the original bone. There is also further swelling and pain around the formation of this bony lump. Eventually the new bone becomes visible under the skin of the leg, in a lump known as a splint. This lump, once it has formed, may change shape and become smoother, but it is permanent.

Splint bones can also fracture - much as my own shin bones did! - but this causes a widespread swelling and the horse is more lame, for a longer period.

Splints form in three ways, known as true, false and blind splints.

A true splint is when the ligament between the splint bone and cannon bone tears. The swelling will appear on the groove between the splint and cannon bones.

A false splint is caused by concussion or other trauma to the cannon bone, and is seen on the outside surface of the splint bone. This kind is usually caused by kicks.

A blind splint occurs on the inside surface of the splint bone, and is very difficult to detect as there is no outward swelling as there is with other splints.