FORELIMB INTERFERENCE

Stephen E O'Grady, DVM, MRCVS

Introduction

Forelimb interference in the horse is a gait abnormality that occurs when the shoe or hoof of one limb strikes the opposite limb anywhere from the coronet to the knee. Interfering most commonly occurs in the fetlock area. Forelimb interference can occur at the various gaits of the horse but is usually noted at the trot. Continual interference can lead to a decrease in peak performance and often results in wounds and soft tissue swellings on the limb that have potential for infection.

Causes of Interference

Among the various causes of interference that have been documented are: forelimb conformation which will dictate the flight pattern, changes in riding or training may accentuate a given gait, and improper farriery.

The conformation often associated with forelimb interference is the horse that toes out with a narrow chest (base wide). If we take a closer look at the limb alignment, we will see that the leg is straight but the limb is rotated outward at or above the knee. This conformation forces the horse to breakover on the outside of the foot and land on an inward arc toward the midline.

Horse's gait and flight patterns can be changed by using a different rider and through various riding and training techniques. A fault in the gait can also occur if the horse's equipment is not properly adjusted. Trimming or shoeing that is incorrect for the individual conformation of the horse or changes in the angulation of the horse's limb can lead to interference. Changes in the position, length or angle of the foot can alter the flight patterns of the hoof or the timing of gaits during movement.

Stumbling

Stumbling is felt to be a form of interference. Stumbling could be considered to be interference with the ground. The stumbling is often blamed on a horse that is lazy or the horse's hoof is long and in need of trimming. Although the long toe can be responsible in some cases, it may be the exception rather than the rule. Shortening the toe of the foot and increasing breakover should correct the problem if hoof length is the cause. It is this author's opinion that a more likely cause of stumbling is heel pain. This will force the horse to land on its toe to avoid the discomfort in the heels and promote stumbling. A thorough lameness examination including diagnostic anesthesia is used to confirm or rule out heel pain. Another remote possibility for subtle stumbling is a neurological disease such as EPM.

Determine the Cause of Forelimb Interference

The best approach for correcting a gait fault will be determined by examining the animal's conformation and foot flight pattern. The forelimb conformation should be accessed with the horse standing squarely on a hard surface. The position of the horse's feet whether the foot turns in or turns out, the presence of a wide or narrow chest and the direction the knee faces should be noted. The horse should be observed walking and trotting directly away from and toward the examiner. Here the examiner is able to observe the flight pattern and the manner in which the foot strikes the ground. The information gained form this brief examination will allow the examiner (farrier) to formulate a plan to correct the particular gait abnormality.

Preventing Interference

Most cases of forelimb interference can be prevented or improved by corrective shoeing. For occasional interference or interference encountered during certain phases of training, protective boots are often more helpful than changing shoes or hoof angles. Changing riders or riding techniques can improve many limb interference problems. Some horses cannot be completely corrected while others will improve only temporarily.

There are several approaches to preventing interference in the fetlock area. Horses that tend to interfere will breakover on the outside of their front feet rather than the middle of the toe. The point of breakover can be detected by examining the wear on the hoof or how the horse is wearing the shoe at the toe. The breakover can be shifted toward the center of the toe by using a square-toed shoe. Using a cinder block as an example to illustrate the mechanism of a square toe shoe, when you push it over, it will fall straight and not to the side. Lateral (outside) support of the toe at the moment of breakover can also be achieved by using a lateral extension-toed shoe. Shoes used on horses that interfere should be rasped or smoothed with a grinder so there is no sharp edge to cause damage if the horse strikes the opposite limb.

The flight pattern of the feet will need to be widened in many cases. The hoof flight pattern of a toed-out horse may be widened to some degree by lowering the outside hoof wall and rasping off flares, especially those on the inside of the hoof wall. Shims or wedges may be placed between the shoe and the hoof in extreme cases to increase the distance between the limbs during movement. Bear in mind that these changes to the feet only manipulate the timing and direction of the gait rather than changing the gait itself. Fatigued horses commonly interfere. A lighter shoe such as aluminum may be of benefit here.

Knee-Hitting

Knee-hitting, also called knee-knocking is rare in performance horses. It occurs when the inside of the front foot strikes the knee on the opposite limb. The cause of knee-hitting is basically the same as described for fetlock interference except that in addition the foot will twist at the moment of breakover. Besides the prevention or correction described for fetlock interference, jar calks welded on the heels will hold the foot on the ground at the moment of breakover and reduce the amount of twisting.

Elbow-Hitting

Elbow- hitting is interference between the heel of the shoe and the elbow of the same leg. Again, this form of interference is rare. It is mostly seen in horses that work at speed or gaited horses. Continual elbow-hitting can cause a shoe boil to develop. Reducing the weight of the shoe and increasing the hoof angle may correct horses that hit their elbows.

It is this authors experience that many horses hit their elbows because of excessively long pasterns. In this case bandaging the fetlock with a light bandage during work will eliminate this type of interference.

Prepurchase

All types of interference can be detrimental to peak performance in the horse. It is important to look for this potential problem during a prepurchase examination. The examiner should look for scars or fibrous thickenings along the inside of the horse's leg. Strict attention should be paid to the animal's conformation and observing limb movement on a hard surface. Often it can be determined whether a horse has interfered in the past or if it is inclined to interfere when placed in strenuous work.
 


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