Why horses develop splints

Conformation and training schedules can contribute to this common inflammatory condition affecting the horse's cannon bone.
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Question: I have a 6-year-old, off-the-track Thoroughbred that I’m retraining for the hunter show ring. The problem is he keeps popping splints. He’s had three in the past 18 months: two on one leg and one on the other. He goes lame when they first show up and are soft. With ice and bute and rest, the lump hardens and he’s sound again, but we lose a lot of training time. Are recurring splints a sign of weakness in the bone? Will he eventually grow out of this? Is there anything I can do to prevent them?
Name withheld by request

A rider inspects the leg of a bay horse.

Recurrent splints in adult horses can be caused by poor conformation or direct trauma to the limb.

Answer: “Splints” is the colloquial term for a boney reaction involving the small second or fourth metacarpal/ tarsal bones adjacent to the cannon bone. As you correctly state, the condition is often painful initially but typically subsides quickly as new bone is formed to stabilize the area. As for causation, in most cases mild instability between the bones results in inflammation and callus (bump) formation. When these are “set” (that is, a mature bone callus has formed), the “splint” typically doesn’t bother the horse. I’d also note that, as horses age, the ligamentous union between these bones naturally mineralizes so not all splints cause lameness. In your horse’s case, however, acute re-injury seems to be occurring in various areas.

“Bench” knees (offset knees) and other knee conformation abnormalities make splints more likely because they result in asymmetries in the forces traveling down the leg. When recurrent splint episodes occur, especially in adult horses, conformation needs to be assessed to determine the risk of future episodes in the same or other limbs. Input from a remedial farrier may help load the limb differently, reducing the risk of recurrence.

Direct trauma also can cause a splint, especially if the horse interferes with the opposite limb during foot-flight or even in the stall. Trauma can create microfractures, and the resulting instability stimulates inflammation and subsequent callus formation. In these cases, protective boots may be sufficient to prevent recurrence.

Click here to learn what behavior may indicate lameness in horses. 

Less commonly, an underlying condition in the suspensory ligament, which lies to the inside of the splint bones and attaches to borders of these bones, may contribute to the problem. Abnormal strain from the suspensory ligament on the bone can create instability that leads to splints. In your horse’s case, the transition from racehorse to show hunter may be a factor as the bones and interosseous ligaments are being exposed to different strains and loads.

Given that your horse is an off-the-track Thoroughbred, it is unlikely that he has a true bone weakness. It is more typical that, with continued hunter training, potentially adding remedial farriery and/or boots, he will eventually stop “popping splints.”

Jonathan McLellan, BVMS (hons)
MRCVS, Dip ACVSMR
Clinical Director, Florida Equine
Veterinary Associates
Ocala, Florida

Jonathan McLellan, BVMS (hons) MRCVS, Dip ACVSMR,graduated with honors from the University of Glasgow (UK) Veterinary School and undertook a surgical internship at FHB Equine Hospital in Ocala. He is a diplomate of the American College of Veterinary Sports Medicine and Rehabilitation, a Member of the Royal College of Veterinary Surgeons, and an RCVS recognized specialist in equine sports medicine. He has a special interest in challenging lameness diagnostics and the rehabilitation of sports injuries.

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