Technical Articles

Hoof Cracks and Fabric Repair
Robert Sigafoos
Chief of Farrier Services
University of Pennsylvania, School of Veterinary Services
New Bolton Center
2005 Robert Sigafoos

Introduction
Cracks involving the horse’s hooves can create lameness and/or infection in the hoof, often resulting in debilitating lameness and loss of use of the horse. Hoof cracks can penetrate partially through the hoof wall (an incomplete hoof crack), or penetrate fully through the wall into sensitive tissue (a full thickness hoof crack). Acute hoof cracks (i.e., cracks that occur without previous damage to the sensitive lamina immediately underlying the crack) are usually caused by sudden, severe trauma to the hoof. These are common to younger race horses prior to the first race, but can appear in any horse with an otherwise normal hoof. Characteristic of the acute hoof crack is one with a direct path of the crack into (or close to) sensitive tissue, with little circumferential deviation of the crack path (see figure 1).
 

Figure 1. A section cut through the hoof wall perpendicular to the long axis of the hoof: Shows the transverse plane of the hoof An enlargement of the crack section Shows a full thickness crack through the hoof wall and circumferential components of the crack (parallel to and within the hoof wall) Suggest that the crack is chronic in nature.

Chronic hoof cracks are usually the final manifestation of underlying damage to internal structures of the wall, including the stratum medium (mid-section of the wall) and/or the laminar layer. This internal damage may result from cycling of the hoof wall under abnormal or severe loads, systemic disease (e.g., laminitis), or from idiopathic reasons. Typically, chronic hoof cracks have multiple circumferential paths within the layers of the wall. In many cases the stratum externum and stratum internum aspects of the cracks may not be in register, but be separated by 3 centimeters or more (figure 2).

Cracks following circumferential paths tend to follow along the plane of the intermediate filaments within the hoof wall (Kasapi 1997). Intermediate filaments are fibrous proteins that contribute to the cytoskeleton of the horn cells of both the horn tubules and the wall matrix that bonds the tubules together. The intermediate filaments act as a microscopic composite that help to direct hoof cracks upwards and outwards (away from sensitive tissue), reducing the energy of the crack.
 

Figure 2. Chronic hoof cracks can often have multiple circumferential paths. The aspect of the crack on the outer wall (a) is often in a different location from where the crack enters into the sensitive tissue of the lamina (b) (i.e., the outer and inner aspects of the crack are not in register).

Repairing hoof cracks
It is important when planning a hoof crack repair to realize that hoof cracks can move in at least three dimensions: proximal to distal, spreading, and axial to abaxial (figure 3). When these types of multi-axial loads are encountered in structural composites, they are typically reinforced by applying a strong laminating fabric in a 45 x 45 yarn orientation.

Braided fabrics can be used to simplify this orientation, since the yarns within the braid are oriented in a 45 x 45 direction relative to the long axis of the fabric (figure 4).

Figure 4. The yarns of braided fabrics are oriented in a 45 x 45 direction relative to the long axis of the fabric (arrow). This allows for maximum reinforcement of the crack in all three directions.

Polyester braids and Cobra Sox (Kevlar/carbon fiber hybrid) braids are available in tube form (which can be slit lengthwise to open up to a 3” wide “tape”, fig. 5). Vectran/polyester is available in a 3” wide tape.

Figure 5. Polyester tubes and Cobra Sox braided tubes can be slit open to make a 3” wide “tape”. Vectran/polyester is available in a 4” wide flat braided tape that requires no slitting.

Polyester is suitable for most repairs of hoof cracks and small areas of wall loss. High stress repairs, such as race horses, heavy horses, or bridging repairs over large areas of missing hoof wall should be done with Vectran/polyester or the Cobra Sox fabric.

These braided fabrics should be used with epoxy-methyl methacrylate repair adhesives (EquAcrylic, Equilox, Equibond, Hoof-Lite, etc). These adhesives give adequate time to saturate and position the fabric during the repair process. Thoroughly saturate the fabrics with the adhesive and overlap the crack or area to be repaired by at least 2 inches - this will help the repair share the load over a broad area and prevent localized stresses that could cause another failure. Generous use of stretch wrap will secure & cover the repair while it sets and help deliver a smooth hard surface.

References
Kasapi, MA, Gosline JM. Design complexity and fracture control in the equine hoof wall. The Journal of Experimental Biology 200, 1639–1659 (1997)
 

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