Standardbred racehorses are prone to coffin bone wing fractures.
Most horse owners pick up quickly on visible changes to their horses’ hooves. Thrush, cracks, and punctures are issues easily detected and (hopefully) treated. But what happens when injuries occur to structures hidden within the hoof capsule?
The three bones inside the horse’s foot, for instance, can fracture just like any other bone in the body. The coffin bone, the lower end of the short pastern bone, and the navicular bone, which sits behind the coffin bone, articulate together in the coffin joint. Of these three bones, veterinarians say the coffin bone is what horses fracture most commonly.
Reasons for Fracture
The horse’s hoof capsule is designed to protect the bone; the outside horn is hard and immobile, and the sole is tough and resilient. Sometimes, however, this protection is inadequate.
While it’s hard to pinpoint precursors to coffin bone breaks, the primary cause of any foot fracture is excessive impact. “This could be from landing on a rock, or jumping and coming down hard, perhaps with a twist,” says Alicia L. Bertone, DVM, PhD, Dipl. ACVS, Trueman Chair in Equine Clinical Medicine and Surgery at The Ohio State University. “It’s typically a high-impact injury.”
Another reason for fracture could be predisposition; researchers have shown that there are certain risk factors for various areas of fracture. “For instance, Standardbred racehorses are prone to wing fractures,” Bertone explains. “The coffin bone looks somewhat like a horseshoe. Toward the back, one of the ‘wings’ may fracture off.”
Further, cumulative strain can be a culprit in coffin bone stress-type fractures, from speed and repetitive impact rather than a one-point-in-time blow.
Diagnosing a Fracture
Paul Goodness, senior member of a group farriery practice based in Round Hill, Virginia, says coffin bone fractures that do not involve the joint can be tricky to diagnose because the clinical signs (lameness, heat, increased digital pulse, etc.) mimic many other foot conditions. You can suspect a coffin bone fracture right away, however, in any previously sound athlete that comes up lame immediately after exertion, Bertone says.
Generally, veterinarians use nerve blocks and radiographs (X rays) for diagnosis, but Goodness says clinicians might use nuclear scintigraphy, MRI, or a CT scan to pinpoint difficult-to-see fractures. Most owners, however, don’t jump right to these more advanced diagnostic tools because of the expense.
Another diagnostic challenge is that sometimes radiographs won’t reveal a coffin bone fracture (especially hairline or stress fractures) until five to 10 days post-injury, after osteolysis (dissolving of bone) occurs at the fracture site, creating the dark line that is visible on radiographs, Goodness says. But if the horse suffers a fracture down the front of his coffin bone, diagnosis is fairly straightforward. “These horses will be acutely lame, even at a walk,” Bertone says. “There will be heat in the foot, an increase in digital pulses to the foot, and the foot will show positive to a hoof tester examination putting pressure on the foot. These telltale signs would warrant X rays,” which she adds confirm diagnosis in 80% of these cases.
Nathaniel A. White, DVM, MS, Dipl. ACVS, professor of surgery at Virginia Tech’s Marion duPont Scott Equine Medical Center, in Leesburg, says it’s best to radiograph the lame foot immediately, rather than after doing any other diagnostic tests such as nerve blocks. “If it’s a stress fracture that hasn’t separated yet, we don’t want to do a nerve block and jog the horse—because there is a risk of having the bone separate and become fractured,” he explains.
“The horse should have very limited activity so that you don't continue to cause a problem.”
Dr. Nathaniel A. White
The primary goals for treating a coffin bone fracture include immobilizing the bone, reducing inflammation, and limiting the horse’s activity until the fracture heals.
Shoeing/Casting If the bone has not yet separated, treatment generally consists of hoof support using a special shoe such as a bar shoe, says White. This protects the hoof wall and prevents it from flexing and expanding when the horse places weight on it.
Bar shoes with clips and rim shoes are two forms of hoof support when horses fracture the coffin bone.
Photo: Courtesy of Paul Goodness.
“If the fracture goes into the coffin joint, a bar shoe with clips around the hoof is recommended,” White says. “An alternative is a rim shoe filled with acrylic all the way around the foot, to give even support around the entire hoof—the goal is to stop hoof wall movement and use the hoof as a cast (so the joint is immobilized and the fracture can heal). A fiberglass cast can be applied on the hoof initially, to protect it, but a shoe is used for long-term support.”
If the coffin bone is broken into several pieces, there are few treatment options besides attempting to support the foot in a stabilizing shoe. “These (coffin bones with multiple fractures) can heal, but it depends on the amount of joint damage,” says White. The more fractures affecting the joint, the lower the horse’s prognosis for recovery due to the chances of arthritis (joint inflammation) developing.
Reducing inflammation “If the horse is in a lot of pain, anything to make the foot more comfortable is helpful,” says White. Pain-relieving tactics include daily icing and non-steroidal anti-inflammatory (such as phenylbutazone or firocoxib) drug -administration.
Veterinarians frequently inject the coffin joint with hyaluronic acid (HA, which plays a role in joint lubrication) to reduce inflammation. However, “corticosteroids are not recommended for acute fractures because they can inhibit healing (i.e., they mask the pain enough that the horse continues loading the leg normally),” he adds.
Resting the horse Depending on the severity of the fracture, White suggests putting the horse on stall rest and possibly introducing some hand walking. “The horse should have very limited activity so that you don’t continue to cause a problem,” he says. “Stress fracture cracks can take three or four months to fully heal. The horses may be sound in a month or two, but if exercise is started too soon this may create a repetitive problem at that site.”
It’s best to be conservative and have your veterinarian review the healing process. White says regular MRIs to evaluate bone activity, which is evidence of remodeling, can help accurately monitor progress.
If the fracture is a complete break, the horse needs stall rest for two to three months, White suggests. Then if there is no lameness, have your veterinarian radiograph the foot to assess healing and determine if the horse can be turned out. “These fractures can take a long time to heal, often requiring a minimum of six months,” White says. “During turnout the foot is kept in a supportive shoe with clips or acrylic support all the way around the hoof wall. Sometimes a pad is placed under the shoe to protect the bottom of the foot.”
And even if your horse appears sound post-stall rest, a fracture line can sometimes still be seen on radiographs or scintigraphy for up to 22 months. This continued remodeling is yet another reason to take recovery slowly.
Surgical repair When a fracture splits the coffin bone in half from toe to coffin joint, a bone screw across the fracture can provide more stability as it heals, White says. Screws can also help stabilize large fractures at the extensor process, which occur when a piece of bone pulls loose at the top front of the coffin bone where the tendon attaches.
Removing bone chips Chip fractures in the coffin joint at the extensor process—small fragments that are not attached to the tendon—can be removed with arthroscopic surgery. In this procedure the veterinarian inserts a tiny fiberoptic video camera through a roughly one-quarter-inch-long incision to view and remove chips.
Neurectomy In some cases lameness does not resolve completely with other treatments and the veterinarian might perform a neurectomy—cutting the nerves at the heel, which is also called nerving. “This may decrease or eliminate pain from arthritis and is a way to get some of these horses back into exercise when other treatments haven’t worked,” says White.
Bertone has performed neurectomies on many Standardbreds with wing fractures. “After being given 60 to 90 days in rim shoes, with anti-inflammatory treatment, we can nerve them and they go back to the racetrack sooner. The fracture may not be fully healed at that time, but they seem to continue to heal. It appears that racing while the foot continued to heal didn’t make any difference in the final healing,” she says.
Facing These Fractures in Foals
Coffin bone fractures in foals heal swiftly (often with just a month of reduced activity) and generally veterinarians give these patients a good prognosis. “Most foals simply have wing fractures or solar margin fractures,” explains Paul Goodness, senior member of a group farriery practice based in Round Hill, Va. “In these instances we generally don’t do anything special if they can be confined for three or four weeks and are not running and playing at pasture. If we can keep them quiet, with minimal activity, and leave the foot alone, these foals generally heal well. But if they have to be turned out, we must come up with some kind of tiny shoe to help immobilize that foot.”
Young animals generally heal much faster than adults, mainly because their bones are still growing. But this also means the tiny supportive shoe the farrier might put on the foal must be replaced frequently with a larger one. “A rule of thumb when we have to apply a cast or shoe (to a foal) is to remove and replace it every two weeks,” Goodness says. “If you leave one on too long it will do long-term damage by restricting hoof growth.”
Heather Smith Thomas
Because they don’t affect the joint, nonarticular wing fractures and rim fractures normally heal well. There is no associated risk for arthritis development, and the horse can generally return to full soundness.
“Depending on the horse’s use, about 50-60% of (all) coffin bone fractures will heal with resolution of lameness,” says White. Supportive shoeing might help prevent lameness once the horse returns to work.
Fractures affecting the joint, such as a crack down the front center of the bone, take longer to heal and come with more lameness issues. “When these heal, the two pieces tend to form a fibrous union rather than a bony union,” says Bertone. “Several studies have shown that it takes a minimum of 11 months rest, followed by a slow return to activity (to heal). It can be difficult to get these fractures to heal to where the horse might have a chance to be athletic again.”
Generally, the limiting factor is how much arthritis develops in the joint, she notes, which depends on how displaced the pieces are. “It also depends on whether there is fragmentation of bone in the joint,” she says. “A sliver or chunk of bone in the joint can be detrimental. If a person doesn’t rest the horse long enough before trying to get back into work, this type of fracture may not have a chance to heal. Those horses have more risk for arthritis.”
Overall, time and good fortune play a part in prognosis. “There is some luck involved, based on how the fracture was created,” says White. “In any fracture that occurs acutely (with sudden lameness), the sooner it can be looked at, and a decision made regarding treatment, the better.”
Always suspect a fracture should your horse become suddenly lame. Work with your veterinarian to obtain a diagnosis before assuming it’s a stone bruise or abscess, because treatment for these problems are counterproductive for a fracture. Your vet and farrier can help you devise a plan for managing a fracture to give your horse the best chance for optimal recovery.
About the Author
Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog, www.heathersmiththomas.blogspot.com, she writes a biweekly blog at http://insidestorey.blogspot.com that comes out on Tuesdays.