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| www.SpeakingEquine.com | Volume 2, Issue 8 |
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Speaking Equine is brought to you by: Dr. John Canning, DVM (970) 963-4573 www.drcanning.com |
Hoof Cracks and RepairCracks and breaks in a horse's hoof is not unusual. Not paying attention to a crack or break can result in the loss of the use of your horse. You will find breaks and cracks occur in a wide variety of depths, lengths, and locations. Cracks or breaks involving the horse's hooves can result in lameness or infections. This may have serious consequences for your horse and can result in the loss of the use of your horse. A crack may penetrate partially through the hoof wall or it may extend through the hoof wall and into the sensitive tissue beneath the hoof wall. At times, a crack or break in the hoof will require mechanical stabilization to allow healing. In this edition of Speaking Equine we discuss hoof anatomy, foot wounds, causes of hoof cracks, treatment of injuries, and possible outcomes of treatment. In addition, we provide a discussion of techniques used to stabilize the hoof and a case study of an equine hoof repair by Dr. Canning. |
Hoof AnatomyWhat sets hooves apart, and makes them more vulnerable than other skin (dermal) structures, is their function. Hooves are critical to overall equine health and can serve as a reliable indicator of your horse's dermal health. A horse's hoof serves to protect its foot. The hoof, and its underlying structures, is a type of integument like the skin on the rest of the body. Although there are differences in the way the hoof appears compared to skin, there are many similarities in both structure and response to injury. The skin and the hoof are both composed of three layers: the epithelium, the dermis, and the subcutaneous tissue, progressing from superficial to deep. The hoof is formed by epithelial keratinization over a greatly modified dermis (sometimes called the corium) that is continuous with the common dermis of the skin at the coronet/coronary band (the junction between the skin and hoof). The subcutaneous tissue of the integument of the foot is also highly specialized. Unlike skin, which tends to be topographically uniform, the integument of the foot is divided topographically into several regions: wall, periople, sole, and frog. These regions reflect the different appearance, structure, and function of the integument in each part of the foot. The wall is the part of the hoof visible in the standing horse. It extends from the coronet to the sole. The wall grows from the coronet and takes about one year to reach the sole. The wall is highest and thickest dorsally (toward the front of the horse) at the toe. It decreases in height and thickness over the sides (quarters) until it is reflected upon itself, forming the rounded heels at the back of the hoof. The inflected parts continue forward for a short distance as the bars that are visible beside the frog when the hoof is raised. The periople serves as a transition between the soft skin and the hard hoof wall. It starts as a band of soft, rubbery horn a few millimeters thick near the coronet and becomes a thin glossy layer distally (toward the ground). This band widens toward the palmar (toward the back of the horse) aspect where it covers the bulbs of the heels and blends with the base of the frog. The sole fills the space between the wall and the frog and forms most of the underside of the hoof. The sole is slightly concave so that only the distal edge of the wall and the frog make contact on firm ground. The sections between the bars and quarters are called the angles of the sole. The junction between the sole and the wall is the white line. The internal rim of the white line is where a farrier places nails when shoeing. The wedge shaped frog is a pad of soft horn that projects from behind into the sole between the bars. Its wide base closes the gap between the heels, and the frog's bulbs of the heels overhang the heels of the wall. The frog has both a central groove and a groove on each side separating it from the bars and the sole.
Foot WoundsThe specialized layers of the hoof react differently to trauma than the skin does. The hard hoof wall will deflect a minor blow that would otherwise damage skin. Small defects in the outer layers of the hoof are generally of no clinical significance. More serious injury causes cracks that are deflected outward to the exterior surface of the foot instead of toward the dermis. The wall tends to fracture along predetermined planes rather than tear irregularly. The edges of an incision type of wound, for example created by a horse kicking against an edge of sheet metal, will stay together instead of gaping open like skin. Quarter cracks of the hoof wall are common, typically starting at the coronary band and continuing distally (toward the ground). They are usually full thickness extending into the dermis of the hoof and often lead to instability, inflammation, and infection. Avulsions of the hoof wall usually involve the wall at the quarters or the heels and can be incomplete or complete. An incomplete hoof wall avulsion remains attached to the foot along at least one margin, while in a complete hoof wall avulsion the affected wall is completely separated from the foot. Puncture wounds are common injuries to the ground surface of the foot and occasionally occur at the coronary band. CausesDetermining the cause of a foot wound is crucial. Correcting the cause is important both to the repair process and to prevent further injury. While injuries can occur at any time due to accidents, thoroughbred racehorses are prone to hoof injuries because of their occupation (extra stresses and frequent shoeing) and breeding (poor quality hoof shape and conformation). Speed, immaturity, and fatigue can create interference injuries, hoof wall lesions, and foot pain. Interference is when the shoe or foot of one limb strikes another. Causes of interference include poor conformation, exercise surface, rider, immature horse, unfit horse, imbalance due to poor shoeing, and imbalance caused by hoof overgrowth. Removing the cause and correctly adjusting foot balance are the only permanent solutions for preventing hoof injuries.TreatmentBecause there is little research on the way foot wounds heal, practical treatment of these wounds has been based on experience and extrapolation from research on skin wounds. Each veterinarian will have techniques that work for him or her. In this article we will discuss one technique for repairing a quarter crack hoof wound. One problem facing equine veterinarians is that many of the horses that develop quarter cracks must continue to perform. It is essential for the repair to provide strength and stability to the hoof wall defect, allowing the horse to perform without pain during the healing process. Marked lameness, pain on palpation, and a swollen discolored coronary band above the defect are signs of possible infection. When infection is present, the crack will be opened and bandaged with a disinfectant agent for at least 48 hours before the repair. The hoof wall is thoroughly cleaned and dried, and the quarter crack is explored while removing any loose undermined horn. The hoof surface on either side of the defect is sanded and two sets of paired holes are drilled across from each other on either side of the crack. Two pieces of stainless steel wire are bent in a hair pin shape and a small steel tab is placed on each wire. These wires are passed through the holes in the hoof in opposite directions, pulled tight, and bent outwards. The steel tabs prevent the wires from cutting into the hoof wall. Additional sets of these wire units can be added until stabilization of the crack is achieved. The internal length of the crack usually exceeds the external length. In those cases, a drain is placed within the debrided crack. The drain exits at the coronary band and below the crack. The ends of all the opposing wires are now joined together and twisted until there is resistance. There should be no movement in the hoof wall on either side of the crack when digital pressure is applied. Elastic adhesive tape is placed around the coronary band, and the hoof is rinsed with denatured alcohol. A polymethylmethacrylate (PMMA) composite is mixed thoroughly and a layer is applied to the prepared area of the foot filling the quarter crack. A section of strong fabric resembling fiberglass is thoroughly covered by and soaked with the PMMA composite and placed over the prepared area followed by another layer of composite. This is repeated until three sections of fabric have been placed. Then the hoof wall is covered with plastic wrap, and an elastic adhesive bandage is pulled tightly around the hoof wall, compressing the fabric. It takes two to three minutes for the composite to cure. The wrap and bandage are taken off, the rubber drain is removed, and the repair is sanded to remove excess composite. Placement of a shoe is preferable, and gluing the shoe on has several advantages. It allows the foot to be trimmed and shod to a suitable conformation, it allows for more expansion to increase support, and there is no concern with nail placement in the affected quarter. OutcomeThe combination of an implant and a composite in repairing a quarter crack increases the strength and durability of the repair. In many veterinarians' experiences these horses become sound almost immediately and are able to return to successful competition following the repair with no infection or bond failures. Failures in quarter crack repair can result from the use of a composite alone not providing adequate strength and stability, the use of rigid acrylics, and the use of materials with poor bonding capabilities. Determining and correcting the underlying cause and applying an appropriate shoe are important factors in the successful repair of a quarter crack. Hoof cracks are not all unusual in the horse world, and they come in a variety of depths, positions on the hoof, lengths, and causes. While hoof wall material is flexible, it, like most materials, possesses a given breaking point. In this case, vertical shear. The number of corrections that have been employed over the years is a lengthy list.
In some instances, combinations of the above are utilized. Persistent toe cracks, like mentioned above, often have an underlying problem, the crack is the result of underlying hoof wall damage. In many instances, the toe wall for varying reasons is separated on its underlying softer tissue attachments. This separation, if it exists, could be a result of mild rotation of the coffin bone (founder) within the hoof capsule, so-called "white line disease," the result of past hoof trauma (similar to having your own big toe stepped on with subsequent separation), and other problems affecting the hoof wall. In any case, there may be an underlying cause that needs to be addressed. The best way to get further information is with radiographs (X rays) of the involved foot. Hoof Repair Case Study by Dr. John Canning, DVM, Carbondale, COThe initial attempt at repair utilized in this case was appropriate- it just simply didn't work on this horse. The basic principle of hoof wall crack repair is to stabilize the forces which keep the crack in place. Of all the methods listed above, my favorite employs the use of what is termed a composite repair.
It is important to reiterate that the success of repair is dependent upon some basic principles:
Before proceeding further, have your veterinarian and farrier thoroughly examine the foot for underlying defects. The underlying concern is that there is likely a significant imbalance of the hoof capsule, such as a long toe with under-run heels, the nature of the defect may alter the chosen method of repair.
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| The single most important part of equine hoof care is regular inspection. Call Dr. John Canning, DVM (970) 963-4573 | ||||
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We strongly encourage horse owners to seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy. After all, it is your horse's life.
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Speaking Equine® Newsletters and other documents provided pursuant to this service are for informational purposes only. The information is provided "as information only" without warranty of any kind. The user assumes the entire risk as to the accuracy and use of the information. Speaking Equine and participating equine professionals strongly recommend that you consult a veterinarian before providing any medical treatment to animals.
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