When the Bone Breaks
They shoot horses, don't they? We all know about the rather depressing traditional "cure" for a horse with a broken leg. But there's good news--they "shoot" them a lot less often these days. The reason is that remarkable advances in equine fracture repair now mean that many horses which in years past could not have been saved, are not only recovering from their injuries, but are going on to successful performance careers, even on the racetrack.
Alicia Bertone, DVM, PhD, Diplomate ACVS, an equine orthopedic surgeon at The Ohio State University, attributes the change in prognosis for fracture patients to a combination of factors.
"Certainly," she says, "the equipment we're using has improved, and we have more accredited surgeons now who are better trained in the techniques needed for fracture repair. But we also have better anesthesia techniques and recovery facilities. It's the assembly of the team for managing these injuries that has improved so much.
"As owners become more aware that many fractures are now repairable, they're requiring their veterinarians to become more educated as to how to manage a fracture injury and get the horse to a surgical center in better condition. The cleaner and more immobile the fracture site when the horse arrives, the easier it is to repair the damage."
Most racetracks now have equine ambulances and trained emergency technicians equipped with sedatives and commercially available splints like the Kimzey leg saver (designed specifically for catastrophic injuries of the fetlock) and the Farley boot (which resembles a ski boot). Equipment like this can be a tremendous boon in immobilizing a fractured limb before the horse does further damage to the ends of the bone, the skin, and the surrounding blood vessels, and can vastly improve his chances for recovery.
"A fracture is a catastrophic injury," Bertone affirms, "and nine out of 10 cases should have some surgical intervention to assure correct healing. But bone is one of the fastest-healing tissues in the body--it heals faster than tendons or ligaments, and study after study has demonstrated that it heals to 100% of its previous strength. With correct care, most fractures heal within four months, and horses are often back up to their previous athletic potential within a year."
Bertone, who has been doing orthopedic surgeries for more than 15 years, notes that Ohio State has one of the longest histories in the country for dealing with equine fractures. Albert Gabel, DVM, now retired from OSU, was a pioneer in fracture repair, and Larry Bramlage, DVM, Diplomate ACVS, now considered one of the pre-eminent equine orthopedists in the United States, trained under Gabel and was based for many years at the university, where he was instrumental in making fracture repair a viable alternative.
"I consider myself part of the next generation of orthopedists here," she says. "For us, fracture repair is now mainstream; OSU even hosts the annual international fracture fixation course for both large and small animals."
Fracture Hows And Whys
A fracture might be the result of a single, violent event--such as being kicked by another horse--or it might be the end result of repeated wear and tear that outstrip the body's attempts at repair. "Microfractures" in the bone structure are a common response to exercise stress, and if the horse is allowed sufficient recovery time between high-stress efforts, his system will repair these tiny fissures in the bone, reinforcing and remodeling the matrix so it can better cope with repeated stresses. (This process can go on for years--studies examining cross-sections of cannon bones taken from British steeplechase horses have indicated that bone thickening and remodeling can continue until the horse is 10 or more years of age.)
If the bone is subjected to enough force before the body has had time to mend these microfractures, they can multiply, until finally the bone cracks or shatters.
(In addition to stress fractures and those that are the result of sudden trauma, horses can suffer "chip" fractures of the knee, fetlock, or hock joint. Chips sometimes are the result of subchondral bone cysts stemming from developmental orthopedic disease, and often are easily dealt with by arthroscopic surgery.)
Diagnosis of fractures is remarkably similar in the vast majority of cases. Most people report hearing a loud popping or cracking noise when the injury occurs. Soon after, swelling and significant pain occur at the site, along with the inability of the horse to bear weight on the limb. These factors, in addition to radiographic confirmation, all point to a fracture.
Among major fractures, Bertone names several types as being common in racehorses (generally considered the most highly stressed equine athletes).
"Breakdown fractures are the classic racehorse fractures," says Bertone. "A breakdown occurs when the support structures of the fetlock give way, tearing the suspensories and fracturing the sesamoid bones on the back of the ankle as they hit the ground surface."
Typically occurring in Thoroughbreds, breakdown fractures are repairable if the joint is immobilized before the horse does more damage to it. Often, the problem is that the horse continues to gallop on it for a few strides before his rider can pull him up, each stride grinding together bone fragments and damaging the blood supply and the surrounding skin, essentially making hamburger of the area and causing too much injury for the surgeon to repair.
Temporary splints like the Kimzey leg saver, however, have improved the chances of saving horses with this type of injury. Bertone says that through the use of a technique called fetlock arthrodesis, plates and screws can be attached to the bone to help stabilize the joint and eventually fuse it. The result is usually a horse which is sound only for breeding, not performance, but which will be comfortable on the limb.
Another typical injury for Thoroughbred racehorses is the condylar fracture of the cannon bone. Typically seen in the left front leg, a condylar fracture shows up on radiographs as a crack that goes laterally up the cannon from the fetlock joint and out the side of the bone, essentially "knocking a corner" off the cannon bone--a piece sometimes up to six inches long. Condylar fractures also are seen in Standardbreds, typically as a left front lateral injury, or on the right hind cannon in a medial position.
"The hind cannon fractures tend to spiral and go higher up the cannon bone," Bertone notes, "which is unique to harness racing athletes."
Most condylar fractures are the direct result of repeated racing stress.
"Condylar fractures can be incomplete and non-displaced, meaning that the bone fragment hasn't broken away from the cannon and is still in its original position," says Bertone, "or they can be complete and displaced, which is the worst-case scenario. If the fracture is complete and displaced, it's often visible under the skin as a painful bump--and when we incise the area for repair, there will be bleeding and hemorrhage."
Repair for a condylar fracture involves using multiple stainless steel screws inserted in a lag fashion, which compresses the bone fragment up against the parent bone as snugly as possible.
"The goal is to stabilize the fetlock joint for fast healing," says Bertone, "and to align the fetlock correctly so that there are no protruding bits of bone which could later contribute to arthritis."
Even if the fracture is incomplete, Bertone recommends the use of screws as the best method of repair. Depending on the degree of displacement and the amount of damage to the surrounding blood vessels (which are crucial points to healing), condylar fractures usually resolve fairly well, and the prognosis is often good for a return to performance the following year.
Sagittal fractures of the P1 (long pastern bone) are another serious fracture common to Thoroughbreds and Standardbreds.
"This is a fracture straight down the front of the P1 bone," Bertone says. "Just like the condylar fracture, this injury can be either incomplete and non-displaced, or complete and displaced."
A sagittal fracture can also be "comminuted" or in many pieces. A comminuted fracture usually is the result of the bone's shattering during a burst of peak speed.
Repairing a sagittal fracture also is done by inserting screws lag fashion, squeezing the bone fragment up tightly against the parent bone to leave little or no gap, and aligning the joint as smoothly as possible.
"If a fragment is displaced," explains Bertone, "we have to do what's called 'reducing' the fracture, which means we try to replace the fragment exactly where it belongs so that the joint can work correctly when it's healed."
With a badly comminuted fracture, she continues, "you can't always put all the fragments back where they belong, but you do the best you can."
Some fragments might have to be removed. Then the injury is usually fitted with a cast to stabilize it. Bertone estimates that 85% of horses with sagittal P1 fractures can return to their racing careers--an encouraging prognosis.
Dorsal cortical fractures are stress fractures of the front of the cannon bone--bucked shins taken to their injurious extreme. On X rays, a crack on the cannon bone usually will be clearly visible, most often in the middle or the upper third of the bone.
"That area of the bone takes a lot of stress," Bertone says, "and the bone tries to respond by becoming stronger and thicker."
But if the stresses are greater than the time available for healing, something has to give. Dorsal cortical fractures are one of the few types of equine fractures in which the horse might be willing to bear some weight on the injured leg, but the bump on the front of the bone usually is easy to feel with the fingers. One or more screws generally are used to repair this type of fracture, and the prognosis generally is very good for a full return to athletic performance.
Splint bone fractures are another common injury associated with the cannons; they can occur on either the distal (lower) or proximal (upper) portions of the splint bone, with the former being far more common. Although many distal fractures will resolve on their own with four to six months of stall rest, the large bump that results prompts many owners to opt for removal of the fractured portion of the bone instead. This is an uncomplicated surgery with a good prognosis for a full return to work.
Much more catastrophic are cannon bone fractures that shatter the bone across the middle.
"In these cases, you see a loose, dangling leg," says Bertone. But she assures us that some of these injuries, despite their shocking looks, are repairable. "It depends on how much damage has been done to the arteries and the skin of the leg. If the horse keeps galloping on it, the blood supply will be damaged and the leg will be left open to infection, making for a poor prognosis. But some of these injuries are repairable with plates and screws, and sometimes the horse even returns to full soundness if the injury doesn't involve any joints. The best results occur when this sort of injury happens to a foal, because the limb has to bear less weight while it heals."
Performance Horse Injuries
In addition to all of these fracture types which occur in racehorses, there are several others that are more likely to show up in performance horses. One is a fracture of the P2 (short pastern bone), which tends to occur in working Quarter Horses which are asked to perform sliding stops. The hind pasterns are most often involved.
In the case of a P2 fracture, arthrodesis is the treatment of choice.
"We do that because if you just fix the fracture, you always get significant arthritis in the pastern joint later," says Bertone. "Instead, we use plates and screws to help fuse the joint. The pastern is a low-motion joint, so you can fuse it and not change the gait of the horse; in fact, this surgery is about 80% successful.
"What limits it is whether the coffin joint is involved. It's difficult to work with coffin joint fractures because access is limited--you have to work from above, and it's difficult to get the alignment of the joint just right or get a screw exactly where you want it to be."
Fractures of the coffin bone (P3) itself are tackled slightly differently. Bertone says she has seen this injury in virtually every type of horse, from jumpers to draft horses, and that the cause is often unclear. She conjectures, however, that extremely sharp turns, or chance circumstances like landing on a rock, could be to blame for at least some coffin bone fractures.
There actually are two types of coffin bone fractures: the sagittal type, which Bertone describes as "straight down the middle" (most often seen in jumpers and event horses), and "wing" fractures, in which a section from the inside or outside "wing" of the bone cracks or snaps off. "This is more commonly seen as a racing injury," she says, "as a result of galloping on turns. They're trickier because they often involve the joint."
Most coffin bone fractures are treated not with plates or screws, but by immobilizing the foot initially with a cast, then replacing the cast in one to two weeks with a heavy support shoe and thick leather sole pads. Multiple clips, or a metal rim that goes all the way around the wall of the hoof, help the shoe restrict the natural expansion and elasticity of the hoof, essentially acting as a cast. A horse shod in this fashion and rested for about five months, then shod with a lighter shoe that often includes bar support for the sole, has a good prognosis, but coffin bone injuries are slow to heal, and sometimes never resolve entirely.
"Some of these horses have to wear bar shoes all their lives," says Bertone. "I've had better outcomes for (coffin bone fractures) in young animals--from weanlings up to about 2-year-olds. When I see it in a 15-year-old jumper, I have to say the prognosis isn't quite as good."
Some sagittal coffin bone fractures can be repaired with screws. A hole is drilled laterally in the hoof wall to gain access to the bone, and the screw is placed behind the hoof wall--almost as you would countersink a screw in wood.
"The coffin bone is about an inch into the middle of the hoof," Bertone explains, "so you don't see anything once the screw is in place. Pink granulation tissue will quickly fill the hole in the hoof wall, and, as the hoof grows down, you lose the hole and the screw is buried in the center of the hoof. It's tricky, though, because there is a risk of fluid buildup."
Immediate attention to immobilizing the hoof is critical with a coffin bone fracture. Unfortunately, because there is no swelling or obvious fracture site, this injury often is mistaken for any of a number of other types of lamenesses. A bounding digital pulse, an inability to bear weight on the foot, and a sore reaction to hoof-testers usually tell the tale.
A break common to foals and weanlings is a fracture of the olecranon (the point of the elbow), often the result of a kick during rambunctious play, or of falling over backwards, something to which foals are more prone than adult horses.
"Many people don't even see it happen," says Bertone. "They just discover the result--a foal who has a classic 'dropped elbow' stance, and won't bear weight on the limb. It's repairable with plates and screws, and the prognosis is good in young horses," with many going on to exhibit no signs of the injury as adults.
Using screws and plates on the bones of a young growing horse can be a tricky procedure because placement across the growth plates can contribute to abnormalities as the horse matures.
"We try not to place the plates so that they interfere with the growth plates if at all possible," says Bertone, who notes that if this is accomplished correctly, the plates need not be removed as the horse grows.
Other Common Fractures
Two more common injuries of pleasure and performance horses include fractures of the long bones of the upper limbs (the humerus in the forelegs, and the femur behind), and fractures of the tuber coxae, often called a "knockdown hip" or "dropped hip." Fractures of the long bones, usually caused by some catastrophic event such as being hit by a car, a trailer accident, or a violent kick by a pasture-mate, generally demonstrate what Bertone describes as "massive swelling," and unfortunately have a poor prognosis in adult horses, since these bones are
crucial to weight-bearing. (Bertone noted that horses suffering from this sort of injury often suffer laminitis in the opposite, supporting limb.) In foals, the outlook is a bit more promising, although the risk of problems with the "good" leg remains along with the risk of long-term growth deformities.
A knockdown hip, on the other hand, often heals on its own. Usually the result of the horse's banging a hip on a doorframe and fracturing the ilium of the pelvis, a knockdown hip is easy to spot, since the bone fragment tends to sink in and down in the flesh. The injury is non-weight-bearing at first, but since it doesn't affect the hip joint itself, the prognosis is generally good for a return to light athletic work. (Because the major gluteal muscles do originate at the ilium, however, Bertone suspects that a horse affected by this injury would be unlikely to have enough power in his hindquarters for a successful return to racing.) The hip might take as much as six months to heal, however, and the area will never look normal--the depression is permanent.
Naturally, there are a number of other potential sites for fractures, with varying prognoses for recovery. But the techniques for repairing these injuries are, for the most part, very similar--although there is something of an art to placing screws in living bone at exactly the right angles to best encourage correct healing of a fracture.
Methods Of Repair
Bertone says that the fracture repair team at OSU works almost exclusively with specially designed stainless steel screws.
"They're well-designed for the purpose," she says, "and we have had good success with them."
In some cases, the screws are placed permanently, while in other instances, the screws are removed once the fracture is resolved.
"In condylar fractures," she says, "the screws are sometimes removed--depending on the severity of the original injury and how well it has healed. I rarely remove them for sagittal P1 fractures. And in dorsal cortical fractures--which are sometimes treated with a combination of screws and a technique called osteostyxsis, in which small holes are drilled into the bone's marrow cavity to encourage the development of new blood vessels and healing cells--I usually remove the screws eventually."
When plates are involved in a fracture repair, their removal depends on the horse's eventual use.
"I might remove a plate for a top athlete, because extreme exercise might cause pain at the site. But for a pleasure horse who's only being used lightly, I'd probably leave it in there," says Bertone.
Removal of screws or plates might require a second full surgery, but the OSU team has found that many screws can be removed with the horse standing, with the help of sedatives--a far less stressful procedure. Screws are most often removed if an infection has developed, or when they have worked themselves loose and cause irritation and pain. As long as they remain tightly in place, they should cause no problems within the bone, despite the fact that they are considerably stronger and more rigid than the bone tissue surrounding them.
Two new products offering promise for certain types of fracture repair are the lactic acid bioabsorbable screws detailed in last month's issue, and titanium screws, which have the potential to be less corrosive, and more flexible, than their stainless steel counterparts--in short, more compatible with the natural properties of bone.
"I haven't used them (titanium screws) myself," says Bertone, "but they are supposed to interface better with the bone. They are still rather experimental, though, and they're pricey ($300 or more per screw, as compared to about $25 per screw for stainless steel)."
A horse which has undergone surgery for fracture repair might or might not receive a cast to help immobilize the injury.
"We sometimes put a cast on just for recovery (from the anesthesia), sometimes for a bit longer, and some surgeries are fine with just a light support bandage over the sutures," Bertone explains. "We cast only if necessary to establish weight-bearing on the limb, which needs to happen as soon as possible so that the horse doesn't develop laminitis in the opposite leg."
The casting material of choice for horses is a light fiberglass resin, which is waterproof and fast-drying. A new development is a casting foam that molds to the horse's leg and stays soft and malleable. Used under the fiberglass cast, it improves the comfort of the apparatus and helps immobilize the injury site at the same time.
Fracture repair is a field that has grown by leaps and bounds in the last 20 years, and new research is improving the prognosis for horses every day. The best part is that these injuries, which once were death sentences for a horse, now are routinely repaired, saving careers and lives.
About the Author
Karen Briggs is the author of six books, including the recently updated Understanding Equine Nutrition as well as Understanding The Pony, both published by Eclipse Press. She's written a few thousand articles on subjects ranging from guttural pouch infections to how to compost your manure. She is also a Canadian certified riding coach, an equine nutritionist, and works in media relations for the harness racing industry. She lives with her band of off-the-track Thoroughbreds on a farm near Guelph, Ontario, and dabbles in eventing.