Thehorse.com - Full Article
by: Nancy S. Loving, DVM
March 17 2011, Article # 17941
Lameness caused by quarter cracks is a nemesis of horses and owners, and treatment is often a complex and time-consuming process. At the 2010 American Association of Equine Practitioners Convention, held Dec. 4-8 in Baltimore, Md., Steve O'Grady, BVSc, MRCVS, of Northern Virginia Equine, in Marshall, discussed the importance of these injuries and how, with exception of traumatic injury cases, it's rare to see a quarter crack without a concurrent sheared heel.
O'Grady described sheared heels as a common hoof capsule deformation caused by disproportionate loading on one side of the foot. This results in one heel bulb displacing upward relative to the adjacent heel bulb. Tissue on the displaced side between the hoof wall and surface of the short pastern bone changes shape, resulting in constant foot pain in the back of the hoof. Over time, uneven loading leads to hoof capsule distortion, subsolar bruising, corns, hoof wall separation, and quarter cracks.
According to O'Grady, veterinarians and farriers should target and correct sheared heel conformation by stabilizing the heels and repairing the crack. He explained that the hoof capsule's viscoelastic nature normally allows it to deform when stress is applied; yet, hoof capsule distortion occurs when compressive and shear forces exceed its capacity to deform.
This overload of the heel creates structural changes that make the hoof more upright, he explained. This decreases the foot's ground surface contact, the hoof wall straightens, heels contract, and the foot narrows. The overloaded heel rolls under with a hoof wall flare developing on the opposite side of the foot. The ungual (collateral) cartilage (on either side of the coffin bone, thought to function in hoof expansion/shock absorption) becomes trapped on the displaced side, restricting hoof expansion...
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