HEELS NA TRAINER ISSUE 32_Jerkins feature.qxd 17/04/2014 22:20 Page 2
SHUNTED HEELS
SHUNTED HEELS
Avoiding cracks with proactive management Functionally adapted for speed and efficient use of energy, the Thoroughbred foot is thin-walled and light compared to other breeds. This adaptation for speed renders the hoof more susceptible to hoof capsule distortions, or shape changes that interfere with the normal function of the foot, which are: support, traction, shock dissipation, and proprioception. Examples of hoof capsule distortions are under run heels, collapsed heels, contracted heels, flares, cracks, and shunted heels.
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ISTORTIONS are a result of either overloading a healthy structure, causing it to collapse or bend, or can be the result of under loading a structure, such as the case of a contracted heel on a clubfoot. In these cases the heel is under loaded and the toe is overloaded, causing the heel to contract and the toe to flare or dish. Distortions can also result from disease processes, such as laminitis, where the hoof wall in the toe region is separated and flares or dishes. Fungal infections or white line disease can also cause weakening of the hoof and subsequent distortion. In the case of the Thoroughbred racehorse, we have a healthy structure that is put under repetitive high loads. The combination of a lighter hoof with thinner hoof wall and sole depth combined with rigorous speed training makes the Thoroughbred hoof susceptible to distortion. The heel region of the hoof is softer and more pliable than the toe and is designed to dissipate shock. It houses such structures as the collateral cartilages, digital cushion, and an abundant vascular system, al l designed to absorb shock. The toe is more rigid, designed to penetrate the
ground to establish traction. Since the heel is softer, more pliable, and hits the ground first, hoof distortions typically present here first. Speed training puts high force on the heels, which lowers the hoof angle over time. As the angle gets lower, more force is placed on the heel creating a vicious cycle that can be difficult to manage while the horse is in full work. Heel distortions can predispose the racehorse to many problems, such as chronic bruising, heel/quarter cracks, pedal bone wing fractures, and osteitis. Many heel problems tend to be reoccurring. This is because the primary problem has not been effectively corrected. Having knowledge of the etiology of a foot problem will help formulate a successful treatment plan to heal the condition, prevent reoccurrence, and improve the longevity and wellbeing of the horse. One problem that is common all over the world is the reoccurring quarter crack. Quarter cracks rarely occur out of the blue. Almost always they are preceded by a hoof capsule distortion known as the shunted heel, also called a sheared or displaced heel (Figure 1). Shunted heels occur as one side of the heel is loaded more heavily than the other, causing it to
Figure 1
displace upward. As the heel bulb and hoof wall in the heel and quarter regions get pushed up, the wall reaches its limitation on elasticity; and as the heel expands during loading, the wall will crack at the hairline, creating a bleeding, painful quarter crack. As long as the heel is allowed to stay in the shunted position the foot is at high
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