By Dr. Kirby Penttila, Burwash Equine Services

Podiatry in equine veterinary practice is gaining increasing attention. We continue to learn more about the function and biomechanics of the horse’s foot, and develop new and innovative strategies to alter those biomechanics and mitigate problems that lead to lameness in the foot. To achieve a successful outcome, equine podiatry requires a team approach and great cooperation between the owner, the veterinarian, and the farrier. Although a relatively small part of the horse’s body, the foot plays a very important role in soundness. It is simply amazing to consider all of the functions that are occurring in this structure in order to support a horse’s size and weight. It can be even more overwhelming when we start to consider how small changes to the biomechanics of the foot can change the function of the foot, and result in lameness issues for the horse down the road. One of the most common hoof deformities, which develops as a result of a change in the healthy balance and biomechanics in the horse’s foot, is the club foot.

What Is Club Foot?

FIGURE 1

An excellent example of mismatched feet. Note the low heel on the left foot and the high heel on the right foot. Photo courtesy of Dr. Kirby Penttila, Burwash Equine Services.

Many horses have what are known as “mismatched feet” (Figure 1). This occurs when the horse has a higher or more upright hoof angle on one foot and a low hoof capsule angle on the opposite foot. We’ll explore later on how this differs from feet that are defined as “club feet.” Factors that contribute to the development of mismatched feet include the influence of genetics, developmental factors, abnormal exercise or loading of the feet, and pain. If you have ever watched foals or young horses graze, you will likely have noticed that most foals have longer legs than necks, and as such often need to stagger their forelimbs when they put their head down to graze. Many foals and young horses have a tendency to stand with the same limb out in front of them and the same limb underneath them, which creates an increased load on the heel of the limb in front and an increased load on the toe of the foot behind. This difference in load can affect the horse’s foot growth and predispose them to mismatched feet. These horses can be recognized by the disparity in the toe angles (one steeper, one lower), heel height (one high, one low), the size of the hooves, the direction of hoof wall growth, and the difference in the hoof pastern axis (the alignment of the three bones of the digit – the coffin bone, the short pastern bone, and the long pastern bone). This disparity in hoof angles is very common in the horse population, with about a third of sound competition horses affected. It may contribute to poor performance, subtle lameness concerns, and a decreased forward phase of stride on the upright foot. The upright foot tends to land toe first, resulting in bruising at the front of the foot and poor sole growth under the tip of the coffin bone. As a result of the decreased forward phase of stride in the upright foot, the foot with the low angle gets overloaded, which increases stresses on the navicular bone and the deep digital flexor tendon. This foot also has a longer distance from the centre of articulation to the toe, increasing the amount of force it takes to rotate the coffin joint and move the foot forward, which increases the chance that this foot will develop lesions in the soft tissues of the heel or the navicular bone. Management of these horses is similar to management of horses with true club foot.

Related: Therapeutic Horseshoeing

When we contrast mismatched feet with what we refer to as club foot, we make the differentiation based on the severity of the deformity and the underlying reason for development. Club foot is one of the most common deformities in the horse world.   Horses affected with club foot develop a flexural deformity of the coffin joint, due to a shortening of the musculotendinous unit that starts high up in the limb and inserts on the coffin bone in the foot, resulting in an upright conformation of the foot. The muscle belly that controls the deep digital flexor tendon is located high in the limb above the knee at the back of leg. In horses that develop a club foot, the flexor muscle fibres have an abnormal degree of persistent contraction, which shortens the overall length of the muscle and results in a shorter distance from origin to insertion of the deep digital flexor tendon at the coffin bone (in simpler terms, the flexor tendon is essentially tighter and shorter than it should be).  This results in persistent tension on the back of the coffin bone within the foot.

Biomechanically, the tension from the deep digital flexor tendon is overwhelming the opposing forces on the coffin bone, causing a change in the orientation of the bone in the hoof capsule, a broken forward hoof-pastern axis, and subsequent deformation of the hoof capsule over time. These horses are at significant risk of chronic lameness as a result of the abnormal forces on the foot and the deformation of the hoof capsule. Early recognition of this condition and proper intervention can make correction possible.

Grade 1: The angle of the toe and the palmar angle of the coffin bone are 5 degrees greater in the affected foot than the opposite foot.

Grade 2: The growth rings in the hoof wall become wider at the heel than at the toe, the palmar angle increases even further, and the horse’s heel no longer touches the ground when the heel is trimmed or rasped back to the widest part of the frog.

Grade 3: The increased tension of the deep digital flexor tendon eventually bends the hoof wall, creating a dish in the dorsal hoof wall; the palmar angle gets even higher, and the normal slope of the coronary band from the toe to the heel is lost.

Grade 4: The coronary band has lost all slope and is parallel with ground; heel height is equal to or greater than coronary band at toe, giving the foot a very boxy appearance.

Note: The term “palmar angle” refers to the angle of the bottom of the coffin bone as it relates to the ground.

As the severity of the grade increases, the heel is no longer being engaged with each step (it is essentially being held off the ground by the too-tight deep digital flexor tendon), which causes the frog to recess up into the foot. When this happens, the horse tends to load the foot toe first, which increases the amount of pressure on the sole under the tip of the coffin bone. This increase in load slows the growth of the sole in this region while growth continues unchecked at the heel, causing the diverging growth rings that we see.

Related: Do Horses Have Hidden, Ancient Toes?

Radiographs (X-rays) of the horse’s feet play an essential role in both diagnosing and grading this condition, but also in helping to develop a treatment plan. Figure 3 gives you an idea of the structures that are evaluated in a radiograph of the horse’s foot. These valuable radiographs also allow the veterinarian to measure and assess a number of important details within the foot (Figure 4). They can shed light on what exactly is going on within the foot from a biomechanical standpoint and allow the veterinarian to determine the best course of action. A full discussion of these details is beyond the scope of this article.

The structures evaluated in a radiograph of the horse’s foot (right) and their correlation to the structures in the specimen of the horse’s foot (left). Photo courtesy of Dr. Kirby Penttila, Burwash Equine Services

All of the intricate measurements that can be gained from good quality radiographs, to help the veterinarian and farrier team develop the best approach to corrective shoeing for this particular horse’s foot. Photo courtesy of Dr. Kirby Penttila, Burwash Equine Services

Development

A basic understanding of the anatomy of the horse’s foot and limb is required to understand how club foot develops. Figure 5 highlights the structures that are at play in this type of deformity. Horses can be born with this type of deformity (congenital) or can develop the deformity later in life (acquired).

Anatomy of a limb. The structure in green is the deep digital flexor tendon, and the structure in red is the check ligament, which is often cut as a surgical means of treatment for cases that don’t respond well to farriery. Illustration ©Horse Community Journals Inc.

Congenital deformities are relatively uncommon, but often can be corrected fairly easily if recognized early and treatment is instituted within the first two to four weeks of life. There are various theories regarding the trigger for the acquired form of the deformity, but none have been scientifically proven. One theory is the rapid growth of the bone when compared to the deep digital flexor tendon, as a result of overfeeding carbohydrates to the mare while the foal is nursing, or to the foal itself after weaning. Another theory is pain in the limb (from any cause), resulting in a protective withdrawal response in the limb that involves the tendon responsible for this deformity (Figure 5). Genetics have been implied as a contributing factor as well, with some practitioners seeing club foot commonly in certain family lines, or in foals from the same stallion or mare. Again, if these foals are recognized early, we can look for potential instigating causes such as nutrition or pain, and work to address these factors and help correct the problem.

Treatment Options

In young foals, early measures to correct the inciting cause, and the use of special glue-on shoes to address the excess tension of the tendon, can be successful in resolving the flexural deformity.

Related: Do Horseshoes Affect the Hoof Skeleton

In older horses, when club foot has become a more chronic condition, altering the biomechanics of the foot is often the key to management. Radiographs of the feet are essential in providing the information necessary to evaluate the existing biomechanics and determining the appropriate changes that need to be made. The general strategies that are considered when developing a corrective farriery plan are:

• Redistribute the load on the foot by creating a ground surface that puts the heels and the frog on the same plane. In other words, we need to trim the heels back to the widest part of the frog.
• Reposition the breakover point in the foot. This will decrease the tension on the deep digital flexor tendon and subsequently decrease the force on the toe as the foot leaves the ground.
• Heel elevation. This is required to account for the underlying shortening of the deep digital flexor tendon musculotendinous unit, which is what is causing the problem in the first place and something that we typically cannot change. This becomes a critical step when we address the first strategy and trim the heels back to the widest part of the frog. Elevating the heel will effectively load the foot properly, but will decrease the tension in the deep digital flexor tendon. If we don’t do this, these horses can get even worse.

Traditional shoes with wedge pads that transfer load to the heel are a common formula used in horses with club foot. Figure 6 shows a visual representation of what we are trying to accomplish with this strategy. These shoes are simpler than the rockers we’ll discuss later, but unfortunately, wedging the heels to the extent that is often necessary does appear to impair blood supply to the heels and weaken them over time.

The image on the left represents what is happening in a horse with a club foot, where the excess tension from the deep digital flexor tendon pulling on the back of the coffin bone is essentially holding the heel off the ground, preventing the horse from fully loading its heel. The image on the right represents what we are trying to accomplish when we shoe with a wedge pad. As you can imagine, standing for long periods of time as shown in the image on the left is likely to make one’s toe quite sore, compared to standing as shown in the image on the right. Photos courtesy of Dr. Kirby Penttila, Burwash Equine Services

An alternative strategy that is relatively new to Western Canada is rocker shoes (Figure 7). Rocker shoes can be used to alter the forces at play in the foot. Rockering the shoes at a point directly below the centre of articulation (centre of rotation) of the coffin joint, and loading the heel at the widest part of the frog, will decrease the tension of the deep digital flexor tendon, redistribute load to the heel, and provide the horse with a self-adjusting palmar angle. In other words, the horse can choose where to load the shoe to find a palmar angle that is the most comfortable. Farrier Kirk Shaw of Equine Unlimited has been working in partnership with our clinic for the last decade, and has implemented and refined the specialized technique required to fit a rocker shoe to the horse’s foot.

A club-footed horse fitted with a rocker shoe. Photo courtesy of Dr. Kirby Penttila, Burwash Equine Services

Higher grade, more severe club foot (grade 4, or grade 3 club foot that doesn’t respond to corrective farriery) may actually require surgery to correct. The surgical procedure employed to help these feet is known as a desmotomy of the check ligament of the deep digital flexor tendon, which basically means that we cut the ligament that anchors the deep digital flexor tendon to the cannon bone in the mid-cannon bone region. Cutting this ligament can increase the length of the deep digital flexor tendon and decrease the tension on the back of the coffin bone, which relieves some of the abnormal force on the foot that causes the external deformities that we see. In some severe cases that don’t respond to other treatment strategies, we may even consider what is called a tenotomy of the deep digital flexor tendon — cutting the tendon to relieve the pull on the back of the coffin bone.

Related: Flexural Limb Deformities in Foals

Meet Colonel

Colonel is a six-year-old Quarter Horse gelding who presented for concerns over the deformity noted in his hoof wall, as well as his poor hoof wall quality. On presentation, he was noted to have a bend in the hoof wall at the toe, to lack the normal slope to his coronary band, and to have growth rings that were wider at the heel than the toe (Figure 8).

Colonel’s front feet on initial presentation. In the left front, note the dish in the hoof wall at the toe. In the right front, note the more pronounced dish in the hoof wall at the toe, and the lack of slope of the coronary band from toe to heel. Photo courtesy of Dr. Kirby Penttila, Burwash Equine Services

Radiographs were taken to evaluate the biomechanics at play in his feet, and to help determine a strategy for altering them via corrective shoeing. His initial radiographs (Figure 9) showed a very steep palmar angle, minimal sole depth under the tip of the coffin bone, a broken forward hoof pastern axis, and the distortion of the hoof wall at the toe. He was diagnosed with a grade 3 club foot on the right front, and a grade 2 club foot on the left front. In many horses similar to Colonel, we often see remodelling of the tip of the coffin bone from the chronic increased loading, and concussion of the bone due to the increased load on the toe, given the abnormal biomechanics at play. This type of remodelling is certain to result in some degree of pain and discomfort. Fortunately, Colonel presented before this had occurred.

Colonel’s radiographs from initial presentation. The white line on the hoof wall at the toe is barium paste, which is used to mark the outside of the hoof wall to ensure it shows up on the radiograph. Photo courtesy of Dr. Kirby Penttila, Burwash Equine Services

It was recommended that Colonel be placed in what are known as full rocker shoes, with some additional mechanics built into the shoe by the farrier. The hoof wall distortion and his sole growth responded rapidly to these biomechanical changes. His foot had started to make a nice recovery within five months, with over 18 millimetres of sole depth under the tip of the coffin bone and resolution of the dish to the dorsal hoof wall (Figure 10). Since this is an underlying conformational flaw for Colonel, he will likely need to be maintained in a special shoe for life, or risk slipping back into his previous predicament.

Colonel’s radiographs taken just less than five months after starting his corrective shoeing plan. Photo courtesy of Dr. Kirby Penttila, Burwash Equine Services

The club foot deformity has been a challenging condition to manage for veterinarians and farriers alike. If not recognized and addressed early in the horse’s life, it can lead to frustrating lameness and limit a horse’s usefulness. By learning to recognize this condition early on and taking proactive measures to correct the deformity, we can make a world of difference for these horses.

Related: The Well-Fed Foot - Nutrition for Healthy Hooves

Related: Common Hoof Problems

Dr. Kirby Penttila, DVM, is a veterinarian and practice owner at Burwash Equine Services, Ltd. She graduated from the Western College of Veterinary Medicine in Saskatoon, SK, and went on to complete an internship in private practice at Idaho Equine Hospital in Nampa, ID. Burwash Equine Services, Ltd. is an exclusively equine practice in Calgary AB that offers a wide range of veterinary services to a clientele that varies from World Champions and Olympians to backyard horse owners. www.burwashequine.ca.

Main Photo: Courtesy of Dr. Kirby Penttila, Burwash Equine Services