How to Manage a Quarter Crack
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DEC 08, 2010
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1. Introduction
Hoof-wall defects, especially quarter cracks, are a common cause of decreased athletic performance in competition horses and frequently lead to foot lameness.1–3 Hoof-wall defects are generally described by their location in the hoof, such as a toe, quarter, or heel crack.4 A true quarter crack originates at the coronet and extends through the full thickness of the hoof wall into the dermis, leading to instability, inflammation, and/or infection. These cracks can be painful because of infection and/or more commonly, instability caused by movement of the hoof wall, especially the vertical movement of the heel bulb on the affected side. The recurrent nature of quarter cracks involving a performance horse presents a challenging and often frustrating problem for equine veterinarians, farriers, and horse owners, because these horses often need to continue to perform.
Many causes of quarter cracks have been described, such as trauma to the coronet, pre-existing damage to the dermis from infection, abnormal hoof conformation, short shoes, inappropriate farrier practices, or an abnormal landing pattern when the foot strikes the ground. The most consistent finding in all quarter-crack cases is a foot conformation with sheared heels and an abnormal strike pattern during the impact phase of the stride.a In fact, it is extremely rare to find a quarter crack that is not accompanied by limb conformation that leads to sheared heels combined with an abnormal strike pattern.1a Various materials and techniques exist for repairing hoof cracks, but none will be successful unless the cause of the hoof-wall defect is determined and addressed through basic farriery.1–3 This paper will discuss the foot conformation and proposed etiology leading to a quarter crack, appropriate farriery, and a repair technique that has provided consistent results.
2. Foot Conformation
Sheared heels can be defined as a hoof-capsule distortion resulting from displacement of one heel bulb proximally relative to the adjacent heel bulb (Fig. 1).5–8 This disparity between the lateral and medial heel bulb is generally 0.5 cm or more.9 When the weight of the horse is not distributed uniformly over the entire hoof during the landing phase of the stride, one focal area of the foot, usually a heel and accompanying heel quarter, receives a disproportionate amount of the total load. This resultant force leads to a remodeling of the affected heel bulb. The degree of distortion in the affected heel is dependent on the amount of the load sustained by the individual foot. Sheared heels can occur in the hind as well as the forefeet. This continual disproportionate load and the increased compressive stresses placed on one side of the foot predispose the foot to injury such a quarter crack (Fig. 2).5
Fig. 1. Palmar view of a foot with a sheared heel. Note the disparity between lateral and medial heel length and the compression of the structures above the medial heel.
Fig. 2. An acute quarter crack. Note the bleeding.
3. Structural Changes to the Foot
The equine hoof capsule is a viscoelastic structure that has the unique ability to deform when weight is accepted uniformly.10 However, if the unequal load is continually placed on one quarter/heel, over time, structural changes will become apparent. The increased load on one side of the foot causes the hoof wall to assume a steeper angle (that is, the wall becomes straighter). Along with the increased hoof-wall angle, other changes, such as contracture of the heel subjected to the greater load, will soon follow. This decreases the ground surface of the foot, resulting in a lack of expansion on that side of the foot and making the solar surface in the palmar/ plantar section of the foot asymmetrical. Over time, the hoof wall begins to roll under on the affected side, which further decreases ground surface under that area of the foot. The side of the foot that first impacts the ground develops a flare because of bending of the hoof tubules.
Over time, the stresses placed on the overloaded side of the foot exceed the ability of the hoof wall to deform.10 The submural tissue on the affected side will be subjected to excessive compressive forces that result in hemorrhage along with stretching or tearing of the lamellae. It is thought that the exudation of fluid in the submural tissue increases pressure and will eventually disrupt the coronary corium, consequently leading to the formation of a quarter crack. Furthermore, a recent study of a group of horses with quarter cracks showed the free margin of the ungual cartilage above the coronet resulting from the displaced quarter/heel to be less than 15 mm.11 This lack of free margin seems to prevent lateral expansion of the ungual cartilage, leading to increased pressure in the sheared heel and trauma to the adjacent coronet.
4. Mechanism
The presence of a sheared heal indicates a disproportionate weight distribution over a section of the hoof that anatomically cannot resist the additional stresses without distortion or displacement. Horses with conformation that causes the limbs to land and load asymmetrically across the hoof will be subject to this type of deformation. The growth rate around the circumference of the hoof is usually approximately uniform, but regional disturbances in growth rate can occur to either increase or decrease growth. The position of the coronary band is related to the balance between hoof wall growth at the coronary band and the rate of migration of the hoof wall distally. Furthermore, the rate of migration of the hoof wall is a balance between an active process occurring in the lamellae to cause them to move distally and the force on the wall from the ground reaction force. Clinical evidence suggests that hoof wall growth is at least in part, if not predominantly, inversely determined by the force of weight bearing at the ground surface of the wall. If the rate of hoof wall growth exceeds the rate of migration distally, the coronary band displaces proximally. This appears to be the mechanism in horses with sheared heels/quarters. Due to the fact that the growth rings below the coronet are usually very close together where the hoof wall is displaced and that the slow hoof wall growth is most likely related to increased weight bearing (force) by the wall; this would suggest that the wall is forced proximally. Whether or not this is a real phenomenon as suggested by clinical experience has not been confirmed in a scientific manner. [...]
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How to reference this publication (Harvard system)?
(2010) “How to Manage a Quarter Crack”, AAEP Annual Convention - Baltimore, 2010. Available at: https://www.ivis.org/library/aaep/aaep-annual-convention-baltimore-2010/how-to-manage-a-quarter-crack (Accessed: 01 October 2023).
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