Dortmund's defection from last weekend's Clark Handicap took a little spice out of the race, all thanks to a little crack in his hoof. Quarter cracks are relatively common among Thoroughbreds, and while they can take time to heal, they don't necessarily put a horse on the shelf for months, the way a soft tissue injury can.
A quarter crack is a vertically-oriented fissure in the side of the foot, often starting at the top of the hoof and working its way down. Some cracks are wider and deeper than others when they first appear.
The cracks occur as a result of strain on the hoof, particularly in the heel. Often, a horse with a quarter crack will have a long toe combined with a heel that is especially low to the ground, or one side of his heel could be a slightly different shape than the other side. Horses with a low heel have less hoof surface hitting the ground, so the force of each footfall becomes greater on the remaining hoof tissue. Quarter cracks also might occur because a horse places his foot on the ground asymmetrically, landing with one side and rolling the weight to the other.
In the case of the low heel, the tubules that make up the hoof wall material grow forward instead of up and down, which makes them weaker. The soft internal structures become compressed with extra force, creating “crushed heels.” Combine the weak hoof materials with the squished internal structures, and the tough exterior gives way from the inside out.
In many cases, the farrier may be blamed for a horse who develops a quarter crack as a result of hoof shape, but experts say it's not that simple. Quarter cracks are more likely to be a one-two punch of genetics and environment, according to veterinarian and farrier Dr. Eric Redden.
“It is the rare horse that has matching feet inside as well as out,” said Redden. “One front foot is invariably a bit steeper and has the characteristic of increased deep digital flexor tendon tension while the other is lower profile inside and out.”
Those small, natural variations can put one foot under more strain than the other. Thoroughbreds have a long history of frail hooves compared to other breeds, with the layers of keratin that make up their feet often appearing thinner and more brittle. Conformational imbalances can exploit these weaknesses. Racehorse's feet also spend a lot of time on padded, soft surfaces, which can fail to stimulate thick growth of the hoof. Add to this the fact that they're bathed daily, with the constant wet/dry transition weakening the hoof wall, and it's easy to understand why a hoof might crack under pressure.
In Redden's experience, uneven wear can take a toll on the whole leg. He finds that a horse's pastern will change its motion during a footfall when compensating for damage to a heel, which can further compound strain on the foot. Redden actually suspects that musculoskeletal stress as a result of weak or floundering feet could be part of what predisposes horses to catastrophic breakdowns.
The first step in treatment for a quarter track is identifying the cause of the strain — whether it's a conformational issue in the legs, a growth issue in the feet, or an environmentally-influenced weakness of new hoof material. A good farrier can develop a plan to help compensate for these issues in the long-term.
In the short term, a horse may need a few days to recover from the pain of a quarter crack, as the cracked edges of the hoof are likely turned inward, exerting pressure on the foot's internal structures. A farrier will clean and trim the edges of the crack and put a metal patch on either side of the crack, weaving wire in between to discourage the crack from widening. The horse will then be placed in a bar shoe to appropriately distribute weight. In Dortmund's case, he won the Grade 3 Native Diver at Del Mar a few days after the quarter crack was discovered and patched.
“Patches can be great band aids and can help a ton of horses get through a race provided the crack isn't infected, there is enough horn wall to anchor the structural aids (tension wires), and there is adequate mass to recover from the weakened quarter,” said Redden.
Once his foot is supported, many horses will become more comfortable, at which point they can resume training and even race, although the only thing that will cure the crack is time. Eventually, the crack will grow out, the way an injury to a fingernail does. With proper support, the laminae that attach the internal hoof structures to the exterior hoof wall will eventually heal as well.
“The good news is, crushed heels can be prevented and managed, however we can't make it happen doing the same thing everyone else does, all the while expecting better results,” said Redden. “Being aware of how quickly feet change inside as well as out once a horse is in full training, and knowing how to eliminate as many known negatives as possible can go a long way to reduce soundness issues and extend the careers of many horses.”
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