By Dwight Bennett, DVM, Ph.D.
Equine fractures are more difficult to repair and heal more slowly than human or small animal fractures. As recently as 30 years ago, most horses with severe fractures were euthanized or, at best, retired, largely because you couldn’t ask a horse to stay in bed or use crutches to keep his weight off of a fracture while it healed. Today, internal fixation, using screws and bone plates, permits a horse to stand on a broken leg while it heals, often making previously life-threatening fractures treatable. Additionally, new anesthetics and methods of bringing a horse out of anesthesia greatly reduce the probability of developing new fractures and refractures during recovery. However, it’s still an anxious time when a horse whose fracture has just been repaired gets to his feet.
Due to increasing competitive intensity, fractured legs in performance horses are more common than ever. The chance of a successful repair often depends largely on how the horse is handled before he gets to the operating table. If a horse is forced to walk on the broken bone or if he’s transported to the hospital without a proper splint, what began as a relatively simple fracture might be irreparable.
An incomplete fracture, sometimes called a stress or “green stick” fracture, occurs when the bone splits or cracks but doesn’t break into separate pieces. Such a fracture is caused by long-term, repeated stress that weakens the bone, as opposed to a single traumatic event that breaks the bone. Incomplete fractures are fairly common in performance horses.
A complete fracture separates the bone into pieces. A simple complete fracture means the bone breaks into two pieces, neither of which penetrates the skin. A fracture in which the bone breaks into more than two pieces is called a comminuted fracture. Complete fractures commonly occur during intense exercise (e.g. when a racehorse breaks down), or result from a kick or severe accident.
A compound fracture means the end of a broken bone penetrates the skin. Equine skin is thin and easily penetrated by sharp bone fragments.
Most complete fractures are fairly obvious. The fracture sight generally swells quickly, and the horse shows immediate distress. The leg might hang crookedly or an end of a bone might penetrate the skin. A horse with a complete fracture often attempts to move on three legs. Incomplete fractures, however, can be difficult to detect, because they usually cause only mild lameness. Early diagnosis is critical, because an incomplete fracture can lead to a complete fracture. The possibility of an incomplete fracture is one reason that it’s important to have your veterinarian promptly examine any lame horse. A stress fracture can be difficult to detect even on x-rays.
Nuclear scintigraphy (the use of nuclear scanners to detect radioactive materials that, when injected intravenously, accumulate in diseased or traumatized areas of the body) is a highly useful technique a veterinarian can use to detect a hidden fracture. If detected in time, an incomplete fracture seldom requires splinting and generally heals with stall rest alone.
Complete-Fracture First Aid
Horses, unlike smaller quadrupeds, don’t move well on three legs. The inability to use his broken leg, along with the attendant pain, can cause considerable anxiety for a horse with a fracture. Frantic attempts to use his broken leg or to regain balance can cause the horse to damage his leg beyond repair. A horse can turn a simple fracture into a comminuted or compound fracture. Movement of the broken bones’ jagged edges can irreparably damage muscles and nerves. Arteries can stretch and be damaged to the point that the blood flow, which carries factors necessary for healing, to the fracture site is impaired. Fortunately, severe bleeding is unusual even with compound fractures.
Complete-fracture first aid requires prompt stabilization to reduce the horse’s anxiety, thus avoiding further damage. Stabilizing or splinting the fractured limb reduces the horse’s anxiety, because it allows him to regain control of the leg even though he can’t put any weight on it. Once the limb is stabilized, most horses will rest the leg rather than try to use it for support. Whenever possible, a veterinarian should apply a splint to a horse’s fractured leg. He’ll generally stabilize the leg even before taking x-rays or performing any other diagnostic procedures. In some cases it might be necessary for the veterinarian to sedate the horse to relax him for sufficient splinting. However, if the veterinarian can’t come immediately, or if you must transport the horse to the veterinarian, you may have to splint the leg yourself. You will need at least one assistant who’s a competent horseman to help restrain and calm the horse.
Follow these steps to safely splint the horse’s leg.
1. Apply the bandage. Never place wood or other stiff splinting material directly against the horse’s skin. Instead, place a bandage under the entire length of the rigid splint. For a fracture at the fetlock or below, apply a single layer of roll cotton over the skin. Wrap gauze smoothly and tightly over the cotton, then wrap it with elastic tape. A fracture that lies from mid-cannon-bone upward requires several layers of cotton bandage, each layer being no more than an inch thick. Individually cover each layer with gauze and elastic tape. If the layer of the padding is too thick, or if several layers of cotton are tightened with just one layer of gauze and tape, the padding will shift and bunch rather than lie smoothly. The total bandage diameter should be approximately three times the limb’s diameter. Such a thick, layered bandage is called a Robert Jones bandage.
2. Apply the splint. Any lightweight, relatively strong, rigid material, such as wood or PVC pipe split lengthwise, makes an effective splint. Place the rigid material over the bandage and tape it in place with nonelastic adhesive tape. (Elastic tape allows the splint to shift its position.) A splint isn’t meant to align the bones’ broken ends. It severs to take weight off the broken bones and hold in a straight line any joints whose movement might cause further damage. The bones’ fractured ends grind against each other when weight is placed on the leg or when the leg is flexed and extended, thus the rigid materials must extend across all joints immediately above and below the fracture. For example, if the fracture is near the fetlock or pastern, the front surfaces of the cannon and pastern bones should be held in a straight line by splints extending from just below the knee or hock down to the foot. If the fracture is in the area of the knee or in the cannon bone, the knee and fetlock must be held straight. A fracture of the mid-to-upper forearm (radius) must be splinted to keep the elbow and knee from bending, and prevent the horse from raising his leg to the side.
A splint requires two boards or two pieces of PVC tubing that must be placed 90 degrees apart, never 180 degrees. In other words, one board should lie along the outside of the leg and the other should lie along the front or the back of the leg. Placing one board along the inside and the other along the outside of the leg is ineffective, because it doesn’t prevent the leg from bending. Nothing prevents the stifle from bending, hence hind-leg fractures from the hock above are difficult to splint, because the horse’s reciprocal apparatus causes the hock to bend whenever the stifle bends and to straighten whenever the stifle straightens. However, a lateral splint applied over a thick, tight Robert Jones bandage and taped tightly across the hock and stifle angles helps support a leg that has such a fracture.
The first step when treating complete fractures is to maneuver the bone fragments into proper alignment. The horse is usually placed under general anesthesia to perform the adjustment, and specialized equipment might be required to pull large bones into position. Once the bone fragments are properly aligned, they’re fixed in position with casts, pins, screws or plates until the fracture heals. Some simple leg fractures heal with nothing but a fiberglass cast holding the bones in place. Such treatment is usually less expensive than surgical correction. However, the necessity for frequent cast changes under general anesthesia can lead to considerable expense.
A cast might be changed as frequently as every 10 days for a foal, or as infrequently as every six weeks for an older horse. The duration depends on how healing progresses and how the horse’s skin and muscle react to the cast. A cast provides less precise alignment and bone fixation than surgical methods of fracture treatment.
External fixation involves pins passed through bone above or both above and below the fracture and incorporated in a cast. The pins allow the intact bones above the fracture to bear most of the horse’s weight. External fixation is more commonly used in humans and small animals than in horses, because pins strong enough to bear a horse’s weight often require drilling excessively large holes in the bones.
Internal fixation requires the fragments to be compressed together by screws or bone plates applied from the outside of the bones or, less commonly, by various types of pins and other devices placed lengthwise inside the bones. In some cases, the plates or screws are permanently left in place. In others, they’re eventually removed. Although expensive, internal fixation has many advantages. A fracture, repaired under compression, heals more quickly and doesn’t form a bony callus, which could interfere with tendons sliding over the bone. A horse with an internally fixed fracture can bear weight on the injured leg and return to work more quickly than a horse whose fracture is repaired with a cast or external fixation. In addition, internal fixation avoids the complications casts pose, such as pressure sores.
When a plate rigidly immobilizes a human or small-animal bone, the bone tends to lose density because most of the weight previously borne by the bone is transferred to the plate. A less-dense bone is prone to refracture after the plate is removed. In horses, however, density rarely reduces (even in foals), because no bone plate available is strong enough to take more than a fraction of a horse’s weight off the bone. Equine surgeons constantly look for stronger, more rigid bone plates.