By Sharon Biggs(Transcribed from the January, 2006 issue of The Horse: Your Guide to Equine Health)
Looking at a horse's delicate limbs, it's a wonder that those bones can put up with any sort of pressure at all. Equine bones are very tough, but fractures still happen. When they do, even the most stoic of horse owners can feel desperate. But a fracture doesn't necessarily mean the death of a loyal companion or promising athlete. Orthopedic techniques have advanced greatly in the human world in the last three decades, and the equine world has moved in step. Technology has progressed so far that many times even the worst of injuries can be repaired.David Nunamaker, VMD, is the Jacques Jenny Professor of Orthopedic Surgery at the University of Pennsylvania School of Veterinary Medicine's New Bolton Center and a leading researcher in the field of equine orthopedics. He says that whether a horse with a fractured limb lives is based more on economic reality then repair feasibility."It can be an expensive decision for people, and they often decide to cut their losses and move on to a new horse," says Nunamaker. "Even if it's a severe injury, we can often save the horse's life, but we may not be able to get him back to that same competitive level. And the owners may decide to have the horse put down."Simple fractures can set an owner back a few thousand dollars, but complicated fractures can be extremely costly depending on length of surgery, techniques used, and hospitalization. There can be further complications after the fracture is repaired, such as infection. Antibiotics are expensive and dosage is the same as with people--by body weight. Since horses weigh 10 times as much as people, the antibiotic will cost 10 times as much."It's also a quality of life issue," adds surgeon Brad Jackman, DVM, MS, a partner in Pioneer Equine Hospital in Oakdale, Calif. "Fractures in joints can lead to problems later on in life. Also, there are many horses who won't tolerate a long lay-up."Types of Fractures
Not all fractures carry a grim prognosis. All are different, and some are more repairable than others. Fractures in the bones of the foot, such as the navicular and coffin bones, are often the easiest to repair and can be managed through rest and corrective shoeing at a minimal cost.The most common long bone fracture that Nunamaker sees, and the easiest to repair, is the lateral condylar fracture (fracture of the third metacarpal or cannon bone on the distal or lower end). "Although this is commonly seen here at the University of Pennsylvania, fractures in other parts of the country and in other parts of the world are in fact different. It's all based on training, the surfaces animals race and work on, as well as what kind of shoes they wear," says Nunamaker.The lateral condylar fracture, usually seen in racehorses, runs from the front to the back of the leg and up the lateral side (outside). This can often be repaired well enough so that horses can go back to work just as strong as before the injury."This fracture is usually repaired through the use of screw fixation," says Nunamaker. "In other words, we take the piece of bone and press it against the parent bone and stabilize it with screws. If it's displaced, we have to reduce the fracture and apply the fixation."Reducing a fracture simply means putting it back into its original position, a difficult job in itself. The ends override and the muscles are stronger than the veterinarian. Surgeons have to try to get the ends to meet well enough to place screws and plates. It's very time-consuming and requires advanced techniques.Jackman sees his fair share of fractures; however, as he's based in a more performance and competition-oriented area, he sees fewer catastrophic fractures than Nunamaker. "We see mostly Western performance horses, hunter/jumpers, and dressage horses," says Jackman. "Because of this, we see a number of fractures of the second phalanx, which is the second pastern bone. Those (fractures) are relatively common in Western performance horses and usually are caused by a torque-type situation. The pastern is a low-motion joint, and most repairs involve fusing the pastern joint."Fusing a joint might sound daunting, but the pastern is responsible for only 3-5% of the flexion motion of a leg. The coffin joint has significantly more, with the fetlock carrying most of the flexion."A horse can lose 3-5% and still retain athletic function," says Jackman. "When fixing a fracture, it is important to have enough bone above and below the fracture to hold the implants (bone plates and screws). In the pastern, this is achieved by using both the first and second phalanges, which means that you have to span the pastern joint. At the time of surgery, the cartilage in the pastern joint is removed so that once healing occurs, the first and second phalanges become one bone structure."Less easy to repair is the fracture of the first phalanx, which is the first pastern bone. "Often this is in two pieces, but it can also be comminuted, which means the bone can be in three pieces or as much as 500 pieces, kind of like a bag of crushed ice, which will require an external fixator," says Nunamaker. The fewer the pieces, the better the prognosis and the quicker the horse can return to work. The greater the number of pieces, the more likely the animal will be only a breeding animal or will require a change in occupation.Beyond any repair is the comminuted humeral fracture. The humerus lies in the front leg and connects the shoulder to the elbow. In youngsters, this repair can be done, but it is an impossible task in adults. A major nerve runs alongside the bone, and after the bone breaks, the nerve is usually damaged beyond repair. This fracture is most commonly seen on the racetrack.Diagnosis
A catastrophic fracture is often so obvious that a handler or rider can diagnose it himself. The character of the fracture is then further diagnosed via X ray. However, nuclear scintigraphy (nuclear bone scan) has been very useful in diagnosing fractures before they happen, particularly with lateral condylar fractures, P1 fractures, and repetitive motion injuries."We can see something is brewing by noticing the remodeling of bone in the nuclear scan," says Nunamaker. "This has been really effective in reducing the injury rate and preventing fractures. We can see bone lesions, which tells us that a horse's schedule needs to be changed so that the bone can remodel and heal before a fracture actually happens." Remodeling indicates that a bone's changing its composition in response to stress; during the early part of this process, the bone actually gets weaker before getting stronger. Stressing this weakened area can result in a fracture.For example, in the past if a horse demonstrated soreness, veterinarians would suggest a few days of rest. After the rest a horse would be put back into training, and since the bone hadn't had enough time to recover, it would break. Nuclear scans can show these potential hot spots and help a vet understand how long a rest is needed in order to allow a bone to repair.Repair Techniques
Internal fixation is a combination of screws and plates inserted in and around the damaged bone. These techniques allow horses to bear full weight after surgery. The original technology of internal fixation came from the Swiss group called the Association for the Study of Internal Fixation (ASIF), which started for human bone repair in the 1950s. Nunamaker's mentor, Jacques Jenny, DrMedVet, was a Swiss veterinarian who came to the United States in the 1950s and is considered the father of equine orthopedics. Nunamaker took an ASIF course in the early 1970s and began to use the technology in small and large animals. The plates originally created for dogs and cats were then adapted for human use.Internal fixation works well for one or two fractures, but things get a bit tricky when the bone is in more than two pieces. At New Bolton Center, Nunamaker and his colleagues have carried on Jenny's work of developing an external fixation device for horses. This device is most commonly seen in human orthopedics. With horses, the external fixation device acts as a total support so the horses can stand and walk immediately after it is applied."The pins are placed in the bone above the fractured bone, which is the cannon bone, and the device goes all the way down and is glued onto the bottom of the hoof with a metal plate," says Nunamaker. "The device bypasses the fracture and the horse can stand and walk while the fracture heals. The fracture is immobilized and the leg is supported much like a non-weight-bearing cast, but in this case the horse can be weight-bearing."Casts are still used in horses, but today they are made of lightweight fiberglass instead of plaster. Casts are used along with internal fixation to add support when horses are waking up from anesthesia. They are also used with non-displaced fractures when internal fixation isn't needed.Gene therapy research is ongoing, and researchers are learning how to unlock the power of the gene to make fractures heal more quickly by themselves. Nunamaker says some proteins that genes make are effective in making fractures heal."In the future, I think we'll see a lot of proteins being used to try to speed up fracture healing," says Nunamaker. "Eventually those proteins being made within the body by the animal's own genes will be switched on so that fractures will heal faster."Challenges
Recovery from anesthesia is one of the issues researchers continue to study. At this time, new drugs are being developed to help horses wake up without struggling. This is the most dangerous time for re-injury of a fracture."A horse is an animal of flight, so he wants to get up and run away as soon as he can," says Nunamaker. "Generally a horse will try to get up long before he is awake enough to stand. He'll thrash around in the stall, and if he hits the sides of the stall he can actually injure himself and break what vets have just spent hours repairing."Most surgeries have rubber-lined recovery stalls, but at the New Bolton Center, Jenny developed a way to avoid fracture re-injuries due to anesthesia emergence."We have a recovery swimming pool where the animal is picked up by a sling, goes along a mono-rail, and is set onto a giant raft," says Nunamaker. "His limbs are encased in long sleeves that hang into the water. The horse recovers in the swimming pool, and once he's wide awake, he's lifted out of the pool with a sling and set on his feet in his stall. When horses wake up in the pool, they might struggle, but they don't hit anything. Plus they are already right side up with their legs underneath them, so they tend to feel calmer."Open fractures have a high rate of infection and are very difficult to treat successfully. The prognosis goes down with open fractures, particularly with comminuted fractures that occur on racetracks when horses are running 30-40 miles per hour. Racehorses are difficult to stop in the heat of the moment and will often keep running on a fracture."When this happens, the soft tissues will be in terrible shape, the bone will be contaminated, and there will be racetrack material driven into the wound," says Nunamaker. "Infection can be a fatal complication."Horses have recovered from fractures such as these, but they are usually too injured to return to racing and often become breeding animals. This type of injury holds a 10-20% survival rate.Infection can develop with a closed fracture as well. Bones breaking inside the skin go off like a gunshot and cause soft tissue injury. "Sometimes the soft tissues aren't capable of keeping the bacteria out and infections occur," says Nunamaker.Even though implants have come a long way, rigid immobilization is hard to obtain in a horse. "Horses are so powerful that it's hard to get those little edges of the bone to remain together," says Jackman. "Horses have to stand after surgery, and therefore there is usually some motion that occurs in the repair. When a horse walks there is going to be microscopic movement of those bones, which inhibits healing."The personality of the horse is also a factor in healing and recovery. "Some horses know you're trying to help them," says Jackman. "They tolerate the confinement and the aid; some horses just won't tolerate it."Foundering on the opposite foot, called contralateral limb laminitis, is a mechanical stress that occurs from overloading the non-injured foot and is a constant issue during recovery. Arthritis is also a threat further down the line. "Bone is the only tissue in the body that actually heals without a scar," says Nunamaker. "So healing of the bone isn't usually the bad outcome. It's fractures into joints that can cause arthritis."Aftercare
Hospital stays can vary according to the type of fracture and owner ability. Owners have to be prepared to check casts daily and change bandages or splints. The horse's temperature must be taken every day. With external fixators, owners are taught about pin care and can nurse the horse at home until the device is removed. Stall rest is generally prescribed once the horse leaves the hospital, although Nunamaker says it doesn't often afford a great deal of immobilization as horses can still walk around their stalls.Prognosis
The prognosis directly depends on the fracture. With non-displaced lateral condylar fractures, around 70% of horses can go back to racing. Open comminuted fractures are the most difficult and hold the worst prognosis for survival, around 10%. "I think it's important that fractures are correctly diagnosed, and then managed for referral to a surgical hospital so that everything is done to try to limit further damage," says Jackman. "Then we just try to give information to the owner as to what they can expect from an expense standpoint, quality of life standpoint, and usage standpoint. Then it's left to the owners to make the decision."