Popped Splint—Fragile Legs Supporting a Big Body

Jill Thornton

Writer’s Comment: When Dr. Marlene Clarke assigned a lay audience paper in UWP 104F (Writing for the Health Sciences), I was intimidated. Faced with the challenge of taking the complexity of a disease or ailment and making it accessible for a lay audience, I stuck with what I know: horses. Having had these majestic animals commandeer my life for the past 12 years, I was familiar with not only their strength, but also their frailty. I chose to discuss popped splints in this paper because it is an example of how something so small, and seemingly self-resolving, can grow to be detrimental to a horse’s career. In an effort to be as clear and direct as possible, I modeled the paper after a magazine article, breaking it down into sections based on description, prevention, diagnosis, and treatment. With this lay audience paper, I wanted to present the technical aspects of the injury in a way that made the information accessible to not only the average horse owner, but the average person as well.

Instructor’s Comment: For the fourth major assignment of UWP 104F (Writing in the Health Professions), I ask students to take a health-related topic about which they know (or will come to know) a great deal and explain that topic to a lay audience composed of college-educated adults with areas of expertise outside of the sciences. Conceptually the topic is not difficult. But many students who have been immersed in the sciences for two or three years find themselves “dumbing down” their subject or forgetting their readers’ lack of scientific knowledge. Jill avoids both of these pitfalls, and conveys her considerable knowledge of equine anatomy to help the lay reader—perhaps a horse owner or novice trainer—understand a topic that may be of critical importance. Hers is also the kind of lucid and articulate explanation that will, I’m certain, appeal to even those Prized Writing readers without Jill’s knowledge of and experience with horses.
—Marlene Clarke, University Writing Program

10–11 THORNTON_Figure 1.jpg

Hoping for a relaxing ride after a stressful day, you head to the barn, eager to put your worries aside and spend time with your horse. You arrive only to discover he is hobbling around his stall with a brand new lump on the inside of his leg. 

Immediately your mind runs wild at the possibilities: torn tendon, fracture, ligament strain. Anxiety consumes you as the competition season seems to slip down the drain. In all the frenzy you can easily overlook one of the most common and probable answers to your horse’s injury, a popped splint.

Caused by the fusion of two bones, a popped splint is a hard, bony growth that typically affects the inside of the foreleg. While popped splints are common in horses and don’t typically result in long-term complications, early detection and proper treatment can help ensure a full recovery. 

In this article you will find ways to recognize the signs of a popped splint, learn why they occur, and discover new treatments to get your horse back in action. 

A Popped What?

To fully understand what causes and creates this bony growth, some background on the foreleg anatomy is required. Like a human shinbone, the cannon bone lies between the horse’s knee and ankle, or fetlock. Flanking either side of the cannon bone are the splint bones. These are the root of the problem. As remnants of the ancient horses’ toes, the splint bones bear no weight and serve no function in the modern horse’s physiology, but that doesn’t mean they can’t be painful when damaged. 

So What Goes Wrong? 

There is an extremely delicate border between the splint bones and the cannon bone, and in the event of trauma or chronic concussion that fragile contact between the two bones is disturbed. This disruption causes the ligament between the bones to solidify, and a bony growth begins to appear at the junction. To an owner, it may seem that this bony lump appears almost randomly, without 10–11 THORNTON_Figure 2.jpgprovocation, but a number of factors may contribute to the likelihood of splint formation. 

Direct Trauma: Whether a horse is out playing in pasture, working in the arena, or even moving around in his stall, he is an athletic animal that must coordinate his legs appropriately. Much as we can sprain an ankle in our own clumsiness, he can easy smack the inside of his front leg with the other leg. Horses carry so much force behind their movements that if their legs knock together at the right spot, that knock has enough power to seriously disrupt their splint bone, causing those bones to fuse. In most cases the splint bone is displaced enough that it pushes against the ligament between it and the cannon bone. This causes that ligament to harden and new bone to be laid down between the bones, effectively fusing them together. Popped splints are more prevalent in younger horses who are often more active and less careful than older horses.

Concussive Force: As horses move they bear most of their weight on their lower limbs. The cannon bone, the tendons around it, and the joints below work like shocks in a car to absorb the jarring motion that comes with pushing off the ground. The better the horse’s leg is at absorbing some of the motion, the less vibration disrupts the splint bone-cannon bone interface. Two factors influence the overall concussion affecting a horse’s legs: hard footing and conformation. 

Much as a treadmill or cushioned track offers enough give to bring comfort to a runner with bad knees, softer footing can provide a cushion that absorbs some of the vibration of the working horse. If the horse is being worked on extremely hard surfaces over an extended time, eventually the rough and abrasive concussion will cause popped splints. In cases like these the splint bone and cannon bone will fuse on not just one leg, but on all four. 

A horse’s body arrangement, or conformation, also plays a big role in the amount of concussive force the splint bone is exposed to. As mentioned earlier, the cannon bone, the tendons around it, and the joints below it function as the shock absorbers. The angle at which the cannon bone attaches to the joints and bones below it (the fetlock and pastern bone) can result in better or worse shock absorption. A horse with a steeper slope in his foot and ankle conformation isn’t able to flex as much as needed to offset the concussion with the ground, causing a more abrasive motion. 

Conformation: The angles at which horses’ legs are put together affect more than just the concussion. They can change the weight bearing forces as well. The direction the toes are facing, the placement of the cannon bone under the knee, and the closeness of the two front feet can all lead to a predisposition for a popped splint. If both toes are splayed inward or are too close together, the horse is at a greater risk for interference between the legs. If the cannon bone is placed more towards the outside of the knee, it causes weight to be distributed unevenly. The unevenness results in a weakness to the inside of the front legs, making fusion more likely. The necessary balance is much like when constructing a tower out of blocks, the bottom block, or the cannon bone, should be placed directly under the block above it, the knee. If the blocks are placed too far in one direction, any additional weight added, like the horse’s body, will not be supported evenly and can result in instability. 

What Can I Do to Prevent It?

While many of us would like to cover our horses in bubble wrap to prevent all leg injuries, there is no absolute prevention for popped splints. The best thing you can do is have your horse wear splint boots or exercise boots when he is worked or in pasture. Boots add padding and support in the event of interference between legs or of direct trauma. As previously mentioned, to aid in the shock absorption, your horse must be worked on good footing. In addition, popped splints can also be avoided in young horses through proper training. If owners gradually strengthen their young horses’ muscles and tendons, there will be less force on their bones and therefore less of a chance for those bones to fuse. 

How Do I Know for Sure My Horse Popped a Splint? 

As with any injury to your horse, it is always best to consult your veterinarian. Luckily, splints are very easy to 10–11 THORNTON_Figure 3.jpgdiagnosis definitely. Because the main problem area deals with bone growth, a popped splint can be confirmed through X-rays of the leg. 

In addition, ultrasound can give you and your veterinarian more information on where the bony growth is in relation to the tendon and ligaments that run along the back of the cannon bone. Through these techniques a popped splint can be diagnosed quickly and with little doubt. 

My Horse Already Popped a Splint. Now What? 

The fusing of the cannon bone and the splint bone occurs in stages. At the initial fusing, the splint is deemed a Hot Splint because of all the inflammation and active growth surrounding the bones. This is typically the stage in which you begin to see symptoms. Your horse may be extremely tender in the area around the swelling. That sensitive area can often be associated with limping or lameness. At this phase the main priority is reducing the inflammation and swelling. The longer that area is inflamed, the more growth and fusion the bones may undergo, causing an increased risk of complication. At this stage, a splint will often be iced and wrapped with a compression wrap to prevent and reduce inflammation. To prevent any more trauma or concussion to the already aggravated bones, you should reduce your horse’s workload for the next 1 to 3 weeks until the splint reaches the Cold Splint stage. 

The Cold Splint stage occurs when the bones are no longer actively growing and fusing. For the majority of cases, this is the final stage. At this point all the heat is gone but a bony growth remains. Over the next few months to years, the area where the bones fused will continue to change as the body attempts to smooth over the growth, much like a carpenter sanding over the rough edges of a newly built table, to align with the cannon bone once again. This is an extremely long process and the leg might not ever look completely normal; however, at this point in most cases the growth become more of a cosmetic blemish than a functional problem. 

While most cases follow a clear progression from hot splint to cold splint, some extreme cases fail to follow the pattern. As mentioned earlier, in the hot splint stage it is essential to stop the bones from continuing to grow and fuse. This is important to prevent the bony growth from interfering with the tendons and ligaments that run down the back of the cannon bone. For the most part, as the bones fuse and a growth protrudes, the growth stays to the inside of the leg, away from the delicate tendons. However, in some cases, the bone grows more towards the back of the cannon bone, often brushing up against the tendons and ligaments.

While this would not be a problem if the bone surface were smooth and easy for the tendons to slide against, these bones are actively changing, so the surface is extremely abrasive. The contact between bone and tendon becomes like sliding silk against sand paper. With each step, the tendons move against the abrasive bone, causing tiny tears along the tendon. Naturally this process is extremely painful to the horse and often makes him limp or renders him lame for life. Unfortunately without any additional treatment, he will be unable to move comfortably. 

There are two basic treatments for extreme, chronic cases: shockwave therapy and/or surgery. Shockwave therapy uses high intensity pressure waves to stimulate healing. Shockwave therapy is administered through a portable machine and is performed once a week for a period of a few months (depending on the degree of trauma). The machine delivers pressure waves at a certain pulse frequency and energy level specific to the type of injury. In the case of popped splints, the goal of shockwave therapy is to numb for pain relief, increase blood circulation, encourage the bones bordering the tendons to smooth out, and heal any micro tears in the tendon. 

In cases where shockwave therapy isn’t successful, surgery is necessary to return the horse to his healthy and rideable condition. The goal of surgery is to do for the horse what his body can’t by smoothing out and eliminating the splint bone where it is impinging on the tendons. This requires breaking off the splint bone below the area that has fused to the cannon bone and gently shaving down the rest so it is flush with the cannon bone. 

Unfortunately in the past, even with surgery, the bone growth around the tendons has often returned. However, new technology has made it possible to irradiate the bone directly after surgery to prevent more growth. After the surgery is complete, the horse’s leg is placed under a linear accelerator and the bone is irradiated. This prevents the bone from actively growing again by killing some of the cells on the surface of the newly altered splint bone. After surgery the horse is confined to his stall for a month before he can slowly return to his normal state of exercise.

It is surprisingly easy for us to get carried away at the sight of any blemish on our beloved four-legged friends, particularly if it is on one of their legs. But a popped splint doesn’t have to mean the end of your horse’s career. Through early detection and proper treatment your horse should be able to recover fully. In the unlikely event that complications arise, new technologies including shockwave therapy or surgery may make it possible for you and your horse to be back in the show arena in no time.

10–11 THORNTON_Figure 4.jpg

King C, Mansmann R. Lameness: Recognizing and Treating the Horse’s Most Common Ailment. Guilford, CT: The Lyons Press (Equine Research); 1997.

Hedge J. Horse Conformation: Structure, Soundness, and Performance. Guilford CT: The Lyons Press (Equine Research); 1999.

Tufts.edu Massachusetts: Tufts University Evolution and Science: 2000 [Cited 15 May 2011] Available from: http://chem.tufts.edu/science/evolution/HorseEvolution.htm

Stomatex.com. United Kingdom: Liverpool: 2004 [Cited 15 May 2011] Available from: http://www.stomatex.com/applications.htm

Vetlearn.com. Washington: Washington State University Veterinary Medicine: 2010 [Cited 15 May 2011] Available from: http://www.vetlearn.com/Portals/0/PV0410_Fidel_TIP.pdf

Veterinarynews.dvm360.com. 2005 [Cited 15 May 2011] Available from:


Kristen Merala (photos)
University of Missouri Extension (leg anatomy)