Sheared Heels

Stephen E. O’Grady, DVM, MRCVS

A leading cause of hoof capsule distortion is mediolateral hoof imbalance. When the weight of the horse is not distributed uniformly over the entire hoof during landing, one focal area of the foot, usually the heel, will receive a disproportionate amount of the total force of impact. This causes that heel (lateral or medial) to be driven in a proximal direction, a condition which was named Sheared Heels by Moyer and Anderson in 1975¹. “Sheared Heels” is a descriptive term for the structural breakdown that occurs between the heel bulbs with the disproportionate use of one heel. The increased focal impact on one side of the foot results in a weakening of the hoof wall on that side, due to the angle of the wall (wall becomes straighter), the shearing force, which disrupts the laminar bond, and the decreased ground bearing surface of the affected heel. Lameness has been attributed to this condition but we also see a number of sound, normal horses with distorted hooves. However, this compromised section of the hoof predisposes the foot to corns, quarter and heel cracks, fracture of the bar, thrush and may lead to the caudal heel syndrome. In fact, how often do we see one of the above problems when it is not accompanied by a sheared, contracted or under-run heel? Sheared heels can occur in the hind feet as well as the forefeet.

Causes

Improper trimming and shoeing have been blamed as the most common cause of sheared heels. Excess hoof wall is removed from one heel creating an imbalance. Because the heels are a different length and height, a disproportionate force is placed on the longer heel during weight bearing. This causes an abnormal shearing force between the heels, structural breakdown occurs and the affected heel is driven upward. However, with the increased awareness of foot problems by the horse-owning public and with the continued improvement in the quality of horseshoeing, this may not be the main cause of this condition today.

Conformational defects that result in unequal loading may also be responsible for mediolateral imbalance. This scenario is different from the first cause. Rather than landing on a higher longer heel, the conformationally predisposed horse first contacts the ground with one side of the foot prior to impact on the opposite heel. This secondary impact drives the heel upward, resulting in sheared heels. This could be considered an acquired vs. a created imbalance and is most commonly observed with a toe-out conformation. This population of horses may or may not have a narrow chest, they will be base-narrow and the carpus (knee) will be rotated laterally. When viewed from the front, although the entire limb faces outward, the leg from the knee to the ground surface of the foot will form a straight line. With the knee facing outward, breakover follows in this direction, changing the flight pattern of the limb so that the foot lands on the lateral side of the hoof wall prior to landing on the medial side. Using a slow motion video camera, one can actually distinguish the point where the foot contacts the ground on one side from the point where the hoof impacts the surface on the other side. Continual trauma to the affected heel will invariably lead to heel and quarter cracks, heel bruising, focal laminar tearing and chronic corns. In addition, this uneven loading sets up a rotational torque around the point of contact which is transferred up the limb and places undue stress on joints, ligaments and the suspensory apparatus.

Attempting to correct conformational defects through improper trimming and shoeing can lead to sheared heels. In trying to correct toe-out conformation, the lateral quarter and heel are often lowered and the medial heel is left high instead of trimming the foot level. The result may show improvement when the horse stands, but when moving, an imbalance has actually been created or worsened. When trimmed in this manner, the ground surface of the inside of the foot is decreased in length relative to the ground surface of the outside of the foot. In many instances, when a shoe is then applied, the branches of the shoe will be unequal in length, thus decreasing the support and increasing the force of impact on the shorter side.

Diagnosis

The evaluation of hoof balance begins with an assessment of overall hoof conformation with the horse standing on a level surface. Toe length, heel height and foot angle relative to the angle of the pastern are assessed. The gross changes in the foot are proportional to the extent of structural damage and the duration of the condition. When sheared heels are present, the heel bulb on the affected side is at least 0.5 centimeters higher than the opposite heel when viewed from behind the horse². When viewed from the front, the hoof wall on the affected side is straighter and, in severe chronic cases, will begin to roll under the horse. There is a marked flare of the hoof wall present on the side opposite the affected heel due to bending of the horn tubules. When viewed from the side, the coronary band will be displaced proximally above the damaged heel. There may also be a bulge in the coronary band above the point of contact. It is important to view the horse in motion on a hard level surface from the front and rear. This should be done at a walk and a trot. When viewing from behind, the examiner should determine which part of the foot is contacting the ground and which portion of the foot is receiving the impact. The point at which the horse breaks over should be noted when viewed from the front.

The foot should be examined for hoof cracks, hoof wall separations and any signs of thrush due to a fissure in the central sulcus of the frog. If lameness is present, it should be localized to the affected area using hoof testers, diagnostic local anesthesia and radiology. It must be determined whether the lameness is due to or related to the sheared heels, or if another problem is present.

As foot imbalance can begin at an early age, it becomes critical to observe foals walking before trimming takes place.

Treatment

The goal of therapy for sheared heels is to correct the existing imbalance in lame horses and to maintain the health of the foot on sound horses. Treatment consists of relieving the impact on the distorted heel, lengthening the bearing surface on the affected side and increasing the support in that area. Selective trimming accompanied by some form of support shoe has always been the treatment of choice, yet this method has not always been successful in changing the conformation of the foot, i.e. allowing the distorted heel to assume a more normal position. We have been quite successful using a method described by a clinic in California in 1990³ which usually gives us a gross anatomical change in the affected portion of the heel. We have found that the change in the distorted heel following treatment will be proportional to the severity and duration of the condition. This procedure can also be used to maintain those horses with conformational variants that lead to this acquired imbalance. The procedure utilizes the combined talents of the veterinarian and farrier as there is a medical aspect to it.

Treatment begins by removing the shoe. The ground bearing surface of the foot is generally level when the shoe is removed. Any excess sole is removed (mild concavity of the sole is created if possible in the case of a flat sole) and the feet are soaked in hot water kept at a constant temperature for twenty minutes. A “lily pad”^a for frog support is taped to the bottom of the foot and a heavy cotton bandage that surrounds the entire foot including the coronary band is applied. The bandage is then soaked in hot water. The horse is placed in a stall for 24 hours and the bandage is moistened periodically during that time. Keeping the foot moist renders it more pliable so that movement of the hoof capsule toward a more normal physiologic shape can take place around a central focus which is the supported coffin bone. A non-steroidal anti-inflammatory drug (phenylbutazone) is administered since the shifting of the lamina can lead to an inflammatory response and a digital pulse.

The following day when the bandage is removed, the distorted heel will have attained a more normal position depending on the severity of the condition, and the hoof will no longer be level. The ground bearing surface where the shear has been relieved will be higher, as well as the solar surface directly under the point of contact. The foot is trimmed level with a rasp. No more foot is removed than is required to level the ground bearing surface. The horse is re-evaluated at a walk and trot on a hard level surface and the point of contact and the point of load impact are determined. Further selective trimming is performed using a rasp to remove hoof wall under these two areas in an attempt to allow the horse to land flat. With some conformational faults, this may not be possible. When the trimming of the foot is completed, the bearing surface under the point of contact and the distorted heel should be lower than the remaining ground bearing surface. Horses with a long toe should have hoof wall removed from the dorsal surface of the toe in order to move the plane of support in a palmar/plantar direction.

Shoeing the horse will vary according to the severity of the condition. In mild cases, a rigid steel shoe may be all that is necessary. Horses that need more support are shod with a wide web steel bar shoe fit full under the affected heel and extended well beyond the end of the heel. The affected area that has been lowered on the ground surface will be completely relieved from impact when shod and will continue to settle further distally. On horses with severe sheared heels, we employ a full support shoe (egg bar heart bar) to relieve the affected heel completely, transfer additional weight bearing to the frog and promote rapid healing. Wide web aluminum shoes can be used if the athletic endeavor of the horse dictates their use. If there is a heel or quarter crack present, we elect, if possible, to balance the foot (i.e. remove the cause) and then, if necessary, repair the crack at a later date when we have healing present at the coronary band. In most cases, we will just clean up the crack, cover it with a composite material and allow it to grow out. In our experience, patching the crack without removing the cause only results in reoccurrence.

When we see sheared heels in foals, it is usually the result of a conformational fault coupled with improper trimming. Many of these foals that are toed-out have their outside wall lowered regardless of the cause. If the knees are rotated outward leading to this toed-out stance, trimming in this manner will only compound the problem. It is imperative to watch these foals walk at each trimming. Improving the sheared heel is slow and involves trimming the foal level with the impacted side being lowered a few millimeters each time the foal is trimmed. If the condition is severe, the inside hoof wall will begin to roll under causing a decrease in the ground bearing surface. In this case, we attach a composite substance^b to the side of the hoof wall to increase the thickness of the hoof wall to the ground surface and to add support to the heel. This technique does not improve the way the foot lands but will prevent further bending of the fragile wall. The hoof wall will follow the direction of the composite as it grows (i.e. the wall will have less bend). A large number of these foals will improve as they grow. As the chest widens, the rotational deformity improves, changing the landing pattern.

Discussion

Hoof imbalance is a common and controversial problem. Many horses are able to withstand these imbalances and remain sound but depending on the severity and amount of distortion of the hoof, foot imbalance (sheared heels) often leads to lameness. Uneven loading of the foot appears to be an indirect cause of pain in structures above the foot. When dealing with sheared heels, one must rely on dynamic balance wherein the horse is observed in motion and trimming is directed at improving the landing pattern. Geometric balance where the ground surface of the hoof is trimmed perpendicular to the long axis of the limb does not take into consideration conformational faults⁴. Using dynamic balance, we strive to have the medial and lateral aspects of the heel land simultaneously but this often is not possible with horses that have a less than ideal conformation. Many times, improvement is all that can be achieved. That improvement in itself is important because we know that continual abnormal impact on one heel will lead to hoof wall defects. . Theoretically, the prevention and treatment of lameness caused by inappropriate mediolateral imbalance is simple but in practice it is often difficult to achieve. Being aware that sheared heels can lead to lameness, prevention seems imperative. When lameness is localized to a distorted heel treatment becomes necessary, but sound horses with a sheared heel from whatever cause will benefit from correction of the imbalance as well.

References

1. Moyer W, Anderson J. Sheared heels: diagnosis and treatment. J Am Vet Med Assoc 1975; 166: 53-55.

2. Turner TA. The use of hoof measurements for the objective assessment of hoof balance. . Proceedings, 38th Annu Conv Am Assoc Equine Practnr 1992; 389-395.

3. Snow V, Birdsall D. Specific parameters used to evaluate hoof balance and support. . Proceedings, 36th Annu Conv Am Assoc Equine Practnr 1990; 299-311.

4. Balch O, White K and Butler D. How lameness is associated with selected aspects of hoof imbalance. Proceedings, 39th Annu Conv Am Assoc Equine Practnr 1993; 213-214.

a Lily Pad,â Advanced Equine Productions. PO Box 54, Versailles KY 90383.

b Equilox, Innovative Animal Products, 6256 34th Avenue NW, Rochester MN 55901.

Sheared Heels Commentary

It is a common belief that one cause of sheared heels is improper mediolateral balance caused by trimming. While in Africa, I was given a group of horses on a large breeding farm (yearlings and older horses) with which to test this. I lowered one side of the foot excessively, sometimes up to one-half inch, and in no instance did I cause sheared heels. Therefore, it is my contention that the main cause of sheared heels is conformation.