The horse is an animal that displays a remarkable combination of power, speed and grace. Through careful design by Mother Nature, horses have evolved into finely tuned athletes whose slender legs can move more than 1,000 pounds of body weight swiftly across the terrain, power them over huge obstacles and navigate quick turns and sudden stops with ease. It is due to the tremendous weight of the horse and the relatively slender and delicate nature of their legs and hooves that certain fractures are considered catastrophic necessitating humane euthanasia.
Anatomy and Physiology
The horse is designed such that most of his weight and musculature is contained within his neck, trunk and rump. Below his body, the legs are mostly skin that covers bone, tendons and ligaments. The horse is able to achieve such extraordinary athleticism because of the design of his limbs. His bones act as lever arms around the fulcrum of the joints, stretching tight the elastic tendons and ligaments where kinetic energy for movement is stored. As this energy is released from the tendons and ligaments and the horse is propelled forward, the hoof and the joints again ready themselves to absorb the impact of landing in preparation for another cycle of movement. Any significant disruption to this unit, such as a fracture to a major long bone of the limb or complete rupture of a tendon or ligament, renders that limb unable to support weight for the horse.
Since horses spend 99 percent of their lives standing, and lie down infrequently, they are not able to rest a fractured limb until it heals as a human would. This not only presents veterinary surgeons with a huge challenge knowing that their fracture repair must be able to support the weight of an unpredictable 1,000 pound animal immediately after surgery, but also puts excessive strain on the legs and hooves of the healthy limbs. This additional strain on the other limbs is serious, frequently resulting in supporting limb laminitis, which is also a painful and fatal disease in horses.
Fracture Repairs in Horses
Certain fractures are considered completely inoperable because the repairs cannot adequately support the weight of a horse immediately after surgery. Displaced spiral fractures of the radius and humerus in the forelimb and tibia or femur in the hindlimb fall under this category.
The most common sites for catastrophic fractures in nonracehorses are the radius in the forelimb and the tibia in the hindlimb. Fractures to these long bones occur frequently when horses kick each other in turnout. Turning out horses with hind shoes together dramatically increases the risk for a catastrophic fracture from a kick.
Other fractures can be repaired and share a variable prognosis for return to pasture soundness, or even return to an athletic career depending on the type of repair and the location of the fracture. Fractures in the pastern can be repaired by realigning the bones with a metal plate and fusing the pastern joint. Coffin bone fractures can be treated with a therapeutic shoe and stall rest. Stress fractures of the long bones such as the radius and tibia that have not displaced can be healed as well if the horse is kept as still as possible for several weeks.
Fractures in Racehorses
The thoroughbred racehorse can suffer from catastrophic fractures of the distal limb while galloping along the racetrack, unlike the sport horse or pleasure horse where such fractures are thankfully more rare. These racing-related fractures in thoroughbred racehorses commonly occur through the fetlock joint either in the cannon bone or at the level of the sesamoid bones in the back of the fetlock. Research is ongoing to determine how to predict and avoid these racing-related injuries. These fractures are typically considered inoperable as well, due to high rates of complications from surgical repair and poor prognosis for return to athletic function.
In 2006, Kentucky Derby winner Barbaro suffered a catastrophic fracture of his right hind leg. A valiant effort by some of the country's top veterinary surgeons at the New Bolton Center at the University of Pennsylvania was undertaken to try to save his life and heal his badly fractured leg. Barbaro received the best veterinary care available and underwent a series of surgeries to heal his broken leg. While the surgeons were able to repair the broken bones of his right hind leg, Barbaro was an unfortunate victim of supporting limb laminitis in his left hind foot. Despite every effort to avoid and then to treat the support limb laminitis, Barbaro's injury was too painful and his condition too severe. He was put to sleep to relieve his suffering.