On Nov. 6, Cliffs of Moher (IRE) shattered his shoulder during the running of the Melbourne Cup at Flemington Racecourse in Australia and was euthanized. The Williams family, co-owners of the 4-year-old Galileo colt, were stunned and distressed when he broke down.
“That horse was sound as a bell, there's no doubt about that,” owner Nick Williams told Australian broadcasters. “You think, ‘What could we have done?' but I keep coming back to the fact that there's absolutely nothing we could have done because the horse was in absolutely perfect order when he got onto the truck going to the races.”
Shoulder fractures are among the less common catastrophic injuries sustained in training and racing. Dr. Stuart Vallance, a board-certified surgeon whose practice is near Flemington Racecourse, conducted research into shoulder fractures while at the University of California-Davis. He said via e-mail that fractures of the humerus accounted for just 9 percent of musculoskeletal deaths in California's post-mortem data (1990-2008).
The humerus is the lower bone in the shoulder, between the elbow and the scapula. It is a thick bone that spirals slightly and has an uneven surface. The humerus can fracture from the trauma of a blow, such as a kick, a collision with an object, or a fall. Physical stress on the bone also can cause it to develop fractures.
Research into humeral fractures in racehorses done at the UC-Davis's J. D. Wheat Orthopedic Research Laboratory found two contributing factors: accumulation of stress fractures when the horse's campaign is too tough to allow the fractures to repair via bone remodeling, and too early a demand on bones weakened by an extended layoff.
Microfractures are microscopic cracks in bones that occur during high-stress demands, such as workouts and races. Bone remodeling enables this damaged bone to be resorbed by the horse's body and replaced by new, stronger bone. Repair of microfractures takes about two weeks. But if additional stress is placed on the damaged bone by a conditioning program that does not allow the body's repair mechanism to stay ahead of the continuing damage of training and racing, the bone can fail.
Incomplete fractures of the humerus are difficult to recognize because the heavy musculature surrounding the bone tends to stabilize it. A horse may come back from a workout or a race with mild lameness that's hard to pinpoint, and it could be disregarded if the lameness resolves in a day or two. Meanwhile, the crack(s) in the humerus may get worse with each morning gallop until the bone breaks.
Long lay ups
When a horse is laid up for greater than 60 days and its movement is restricted, deconditioning osteoporosis causes cavities to form in the bone, giving it the appearance of Swiss cheese. Meanwhile, its heart, lungs, and muscles also decondition. When the horse returns to training, its bones take longer to fill in those cavities with new, stronger bone than it takes the heart, lungs, and muscles to recondition. The horse may appear to be in robust shape, but unless its exercise program allows enough time and controlled exercise to balance the strength of its muscles and the strength of its bones, a breakdown can occur.
The humerus transfers the energy created by the muscles of the forehand to the leg. If the humerus is riddled with stress fractures and the horse takes a bad step while going at speed, the force created by the powerful muscles attached to the humerus can cause the bone to shatter.
“Unfortunately, the comminuted configuration (many bone fragments) of these fractures make them almost impossible to repair,” Vallance wrote.
Researchers at UC-Davis compared two different lengths of layups and two different training regimens — one that included one, long, high-speed gallop per week and one that featured a shorter, high-speed gallop two days per week. Results showed the longer layup caused less damage to the humerus, as did the training program with two shorter, high-speed gallops.
Difficult to detect
If the horse's veterinarian suspects a problem with its humerus, standard X-rays typically are unable to get a good view because of the bone's location. This is what happened to California Chrome's little sister, Hope's Love. Trainer Steve Sherman, son of Chrome's trainer Art Sherman, noticed the filly's walk was a little off after a gallop one morning. X-rays showed no fracture, but Steve insisted there was something wrong. Further diagnostics revealed a cracked humerus. Hope's Love was laid up to allow the bone to heal, and tragedy was averted. She returned to race seven months later.
Scintigraphy is the diagnostic of choice for humeral fractures. A radioactive isotope is administered intravenously to act as a tracer that attaches to the blood and is distributed throughout the body via the bloodstream. In a healthy horse, the tracer is distributed evenly. However, where there is active bone remodeling or inflammation, a concentration of the radioactive tracer occurs.
After the tracer is injected into the horse, its body is scanned with a special camera, and a nuclear computer interprets that scan to produce an image that shows any concentration of the tracer as a “hot spot,” a red area on the film; areas of diminished blood flow show up as “cold spots.”
The prognosis for complete fracture of the humerus is not good. Any weight on the leg causes the bone to collapse. Additionally, the radial nerve that lies along the humerus may be damaged by the break. Laminitis in the opposite leg is a threat. Most times, euthanasia is the humane option.
Incomplete fractures of the humerus mend with extended time off and restricted movement, such as stall rest, hand walking, and turnout in a round pen or small paddock. For the first two weeks of stall rest, it may be necessary to keep the horse in cross ties to prevent it from lying down because getting up and down can cause the incomplete fracture to break apart. If managed well, the horse should be able to return to its previous level of performance.
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