By Justin High, DVM
In the grand scheme of things, splint bones perform a useful function in horses. Whether on the front or hind limb, splint bones help form the base of support for the lowest joint in the carpus (knee) or the hock.
There are medial and lateral (inside or outside) splints that have an articular component at the top of the bone that supports joint stability, and then run approximately 80 percent of the length of the cannon bone tapering down to a thin sliver of bone at the tip called the “button.” The splint is held tightly to the cannon bone by the interosseous ligament, with only skin protecting it from the outside world.
The reason my first sentence stated splints actually perform a useful function is because most horse owners get introduced to them at the vet when they go lame from “popping” one that causes an obvious lameness. Fractures from kicking the stall wall, or interference with an opposing leg during work, are other sources of injury. Like a lot of things in life, big problems can come from small sources and splints often fit that bill.
The X-ray is an oblique view of the RH leg of a 3-year-old colt that has obviously fractured the bottom tip or “button” off his outside splint bone. He presented with a mild lameness, but fairly significant, localized swelling over the outside of his lower cannon bone/fetlock area. The X-ray shows an excellent view of the relationship of the larger cannon bone to the smaller splint bone with the fracture actually displaced off the plane of the bone’s normal alignment. For more orientation, the top end of the fetlock joint is visible at the bottom of the picture.
As far as splints go, this is a fairly easy diagnosis. The gray area comes in when you begin to start talking about treatment. In all fairness, there are entire chapters in books devoted solely to the problems that come from splints, so for the sake of time let’s just talk about this one. The colt is a pretty salty 3-year-old that is doing well and on track to show in the open of the NCHA Futurity (no pressure there). The pressure comes in when you look at the calendar and it is October 25 (now there’s pressure).
This may sound like a joke, but it’s not. As long as you don’t let a surgeon look at that X-ray, you’ll be fine. I like doing surgery, but I’m not a surgeon, and that X-ray is like taking candy from a baby for someone who likes to cut on horses. Small incision, the bone comes out easily, suture things up, and everyone is happy. The problem comes in when you add the tight time frame on top of the post-op healing. For this horse, we made sure there were no other sources of lameness first. After that, he got the week off with a firm support/sweat bandage, pain meds, etc. and came back like nothing ever happened. Granted, he was watched like hawk, re-X-rayed after almost every work, and babied by the young lady who took care of him, but never missed a beat.
The key to success in this particular case was that the fragment never moved, and it never sequestered. A sequestrum is formed when a piece of bone loses its blood supply by fracture or trauma, and acts like a foreign body causing a wound with drainage from the dead bone. If the fragment had moved towards the flexor tendons/suspensory ligament, or sequestered the horse would have unequivocally required surgery. Thankfully, it never moved a millimeter and I never let him see his own X-rays, so everything turned out great in the end. That was last year, by the way. Still looks the same today.
Dr. Justin High is a veterinarian and partner in Reata Equine Hospital in Weatherford, Texas. He graduated vet school from Texas A&M University and completed an internship at The Littleton Equine Medical Center in Denver, Colo. High’s years of practice focuses on the Western performances horse. Send any comments or questions firstname.lastname@example.org.