Managing hoof wall defects

Introduction

Full thickness hoof wall defects such as quarter and toe cracks, result in a loss of the structural integrity of the hoof wall. They are not uncommon in equine practice and often manifest in lameness. Successful management of these hoof wall defects involves identifying and addressing the underlying cause(s), stabilization of the foot, and committed follow-up ^1,2. Treatment is most successful when the cause is investigated, the appropriate farriery is initiated as early as possible, and when the biomechanical properties of the foot are thoroughly understood. Inadequate attention to these factors accounts for the many failures encountered and the recurring nature of hoof wall defects. The two generally encountered defects are quarter cracks and toe cracks both of which originate at the coronet and migrate distally. Both of these hoof wall defects often lead to infection, lameness and are a common cause of decreased athletic performance in competition horses. Hoof wall defects are generally associated with a hoof capsule distortion, for example, with a quarter crack, the distortion will be associated with a sheared heel on the affected side ³. There is a myriad of materials and techniques described for repairing hoof cracks, but none will be successful unless the cause of the hoof wall defect is determined and addressed through the appropriate farriery ^1,2,3

Pathophysiology of Quarter Cracks and Toe Cracks

Many causes for full thickness quarter cracks and toe cracks have been described including coronet injuries, inappropriate farrier practices, poor quality hoof walls (because of genetics, nutrition, and/or environment), white line disease, and hoof capsule distortion. In the author’s experience, the most common underlying cause of full thickness quarter cracks and toe cracks is a hoof capsule distortion ⁴ .

Quarter Cracks

It is well accepted that the hoof capsule adapts and changes shape according to how it is loaded. Faulty limb conformation adversely affects how the hoof is loaded, and habitual disproportionate loading will change the shape of the hoof capsule over time. The resulting distortion of the hoof may negatively affect its mechanical behavior, resulting in abnormal force and stress within its tissues. The hoof capsule distortion most associated with a full thickness quarter crack is a sheared heel.  A sheared heel is defined as a hoof capsule distortion resulting in a proximal displacement of one quarter/heel bulb relative to the contralateral side of the hoof 3,5. If the changes in forces and stress become excessive, the hoof wall will be predisposed to injuries such as a full thickness quarter crack.

Toe Cracks

Full thickness toe cracks originate at the coronet at the center of the dorsal toe and extend distally. There is generally a proximal to distal concavity present in the dorsal hoof wall. The crack will open when the foot is unloaded and close when the load is applied to the foot. Toe cracks are generally seen in horses with excessively upright or club feet 2 . With this conformation, the heels are generally allowed to migrate dorsally and/or the shoe is too small. This limits the solar surface of the foot in the heel area and places further load and leverage on the toe section of the foot.

Management of Quarter Cracks

Affected feet should be trimmed appropriately using the guidelines of a parallel hoof-pastern axis, center of rotation bisecting the weight bearing surface of the foot, and the heels of the hoof capsule extending to the base of the frog or trimming the heel area to ensure the frog and the hoof wall are on the same plane.¹

If the situation permits, the horse’s shoes should be removed, the feet are trimmed as described above and the horse is then stood on a hard surface for at least 24 hours prior to trimming and shoeing. This allows the affected side of the foot to settle into a more acceptable conformation prior to completing the farriery. A “double trimming” technique can be used where the affected foot is first trimmed as described above, a shoe is fitted and then before attaching the shoe, a second trim is performed under the proximally displaced quarter/heel. The second trim begins at the ipsilateral toe and is trimmed in a tapered toward the heel. The foot is then shod with a symmetrically fitted wide web steel straight bar shoe, with the trim creating a space that resembles a wedge between the affected quarter/heel and the shoe. This will effectively unload the distorted side of the foot

Ideally, horses with full thickness quarter cracks should be taken out of work allowing time for inflammation to resolve and the crack to begin to be replaced by new wall at the coronet before they are repaired. If the horse has to continue in work, my preferred technique for stabilizing quarter cracks involves inserting an implant composed of stainless steel wires first, and then reinforcing the wires with a “patch” consisting of a mix of fiberglass strands and polymethylmethacrylate adhesive (Equilox Pine Island, MN).

Management of Toe Cracks

A toe crack associated with an upright or club foot hoof conformation should be trimmed to establish a parallel hoof-pastern axis along with attempting to shift the load away from the toe and onto the palmar section of the foot. This can be accomplished by beginning the trim in the middle of the foot and trimming the foot in a tapered fashion toward the heels. The concavity is removed from the outer dorsal hoof wall and a larger size shoe is applied.

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