2014 Podiatry Program Proceedings

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Mission Statement

The mission of the NEAEP is to improve the health and welfare of horses by providing state- of-the-art professional education and supporting the economic security of the equine industry by complementing established local associations and giving equine veterinarians, farriers, technicians, veterinary students and horse owners a unified voice at the state and regional levels.

The American Association of Veterinary State Board, RACE Committee, has reviewed and approved the program referenced as meeting the Standards adopted by the AAVSB. Additionally, the Podiatry Program has been approved for 24 American & Canadian Association of Professional Farriers (AAPF/CAPF) Continuing Education Credits.

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Table of Contents

Shoeing for Soundness: Sport Horse Lameness and Biomechanics of the Distal Limb ...... 4 Shoeing for Soundness: Coffin Joint Function, Pathology, and Treatment ...... 9 Applied Anatomy of the Equine Foot ...... 16 Biomechanics of the Stance ...... 21 Trimming Fundamentals and Foot Pathology ...... 22 Physiologic vs. Pathologic I – Functional Implications for the Farrier ...... 24 Physiologic vs. Pathlogic II – Adaptive Shoeing Concepts ...... 29 Traction – External and Internal Factors that Affect the Biomechanics of the Stance ...... 35 Complicated Feet, Case Studies ...... 36 The Upright Hoof Capsule (Are Farriers Producing Club Feet) ...... 37 Podiatric Considerations in the Soundness Exam ...... 38 Footing/Movement – Limb Injuries: What the Horse Brings to the Table ...... 43 Hoof Capsule Distortion, Parts 1 and 2 ...... 44 Diagnostic Imaging of the Foot in Sound and Lame Horses ...... 50

3 Shoeing for Soundness: Sport Horse Lameness and Biomechanics of the Distal Limb Mark Silverman, DVM, MS Sporthorse Veterinary Services San Marcos, California

The foot is a complex system of integrated structures performing many functions for the equine athlete. While comprising only a small percentage of the horses’ overall mass the foot is responsible for many factors essential to proper function and survival. The goal of today’s presentation is to examine the biomechanical evolution of the modern horses’ distal limb. Through improved understanding we can optimize our approach to shoeing for performance and soundness.

There has been a roughly 70 million-year evolution to arrive at the structure of the modern horse. The Hyracotherium (Eohippus) was the evolutionary starting point for today’s horse. This creature was about the size of a fox and had multiple digits on the end of each limb. The path of evolution was driven by changes in available food sources and environment. These regional changes favored the ability to cover great distances efficiently. In addition, as a prey animal, the horse needed the ability to mount short to moderate distance bursts of great speed. The ability to deliver this duality while carrying a large herbivorous system required a series of adaptations.

The relatively rigid structure of the thorax and abdomen dictated that the limbs must be the primary drivers of the horses’ speed and efficiency. The proximal bones of the limbs grew more compact and the muscles responsible for limb movement stayed within the contour of the body. The bones of the distal limbs grew longer as did the associated tendons and ligaments. These changes promoted the function of the tendons and ligaments as energy stores during locomotion while keeping the lower limbs light and making the system efficient. The bone structure of the limbs became simplified and a singular toe evolved, again to improve speed and efficiency and durability in the harsh terrain. The stay apparatus developed into an effective suspension and energy return system.

There were compromises made in the course of these adaptations. The long levers that allow the system to perform lent to an increased risk of structural failure of both bone and sinew. Another factor of the modern system was the relative loss of pronation and supination of the distal digit. The more proximal articulations are restricted to motion involving flexion and extension. This is the case for the elbow, carpus and especially the fetlock joint. The restricted degree of freedom of the fetlock is crucial to the function of the suspensory apparatus and its ability to store and return energy.

The function of the this lever and spring system allows the horse both speed and efficiency of movement, but the system had need of a method of coping with the rigors of undulating terrain and changes of direction. These challenges fell upon the most distal portion of the limb. The pastern and the coffin joints incorporate added degrees of freedom to allow for following terrain and the demands of turning. The hoof capsule itself is an additional portion of the adaptive mechanism. The limb’s ability to accommodate turns and irregular terrain is all focused below the level of the fetlock.

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Image1 Angular demands of turning. Image 2 Compensation focused on coffin and pastern joints.

Beginning with the most proximal structure involved in the adaptive system, we have the pastern or proximal interphalangeal joint. Through a combination of both minor rotational and collateral movement the pastern accommodates a small amount of the required range of motion required for successful function of the horse. Next up the bony column we have the coffin or distal interphalangeal joint. The design of this complex joint allows for both collateral and translational or sliding movement of the joint. The coffin joint copes with the lion’s share of the demands of turning and limb angulation. This joint, through all of its complex range of motion, becomes more stable as the demands for movement outside of the sagittal plane increase.

Image 3 Compensation for angular demands are focused below the metacarpophalangeal joint. 5

The hoof capsule itself is the next part of the equation. The complex shape of the ground surface allows the hoof to work with the terrain, cutting into a forgiving surface, thus minimizing the demands for compensation on the joints. In addition, the capsule itself is plastic in nature and can deform to accommodate irregularities in terrain or lean angle when turning. Though dedicated to small portion of the body, this system allows for useful accommodation of the challenges facing the horse in many scenarios. However, when the available range of motion is exceeded, these structures bear the brunt. Momentary extremes or repetitive challenges at the limit will lead to injury of the soft tissues working to stabilize the joints. Collateral ligaments and joint capsules will stretch beyond their ability to rebound and can potentially tear. Joints will suffer damage to the protective cartilage that allows for smooth and pain free gliding of the joint surfaces. The joint may even be placed in a situation that demands an excursion beyond the congruence of its sister surface, leading to potential damage. Laminae, joining the bony P3 to the tough hoof capsule can be challenged to the point of tearing and separation.

Enter into this equation the demands placed on the performance horse. The added requirement for traction or wear resistance or alteration of gait has lead to the placement of shoes on the hooves. This addition of this seemingly minor rim of metal has consequences of great magnitude. Bear in mind that I am not advocating for or against the use of shoes. There are many good and valid reasons for the use of some sort of appliance on the hoof’s ground surface. It is up to us as hoof care professionals to fully comprehend the effects of what we are tampering with when a shoe is placed. Never mind the changes in the ground/sole interface, there are ways to mitigate or even improve this interaction. What is of great concern is the loss of the hoof’s ability to deform in accommodation of the demands of work. By taking this factor out of the equation we add to the challenge of the remaining components of the formula. Keep in mind that the demands of angular adaptation on one side of the equation don’t change. This leaves us with fewer components to cope with the challenge, each taking on greater responsibility and therefore greater risk of failure.

This scenario leaves us with the task of how we might approach a patient when we are aware that we are taking something away from them when a shoe becomes necessary or desired. From experience we have all become aware that as a mentor of mine once put it, “you can’t hardly f—k up a good one”. We can inadvertently add to the “good one’s” repetitive stress, and we can certainly help to put a marginal patient over the edge by limiting his natural ability to adapt. What can we do to balance this equation?

Through recognition of the detailed biomechanics of the limb we can shoe to limit the demands of motion. If we allow the shoe to do some of the work of angular adaptation we can limit the extreme demands placed on the structures of the limb. This question was answered in a completely ‘out of the box’ fashion with the Seattle shoe back in the 1980’s. By allowing the shoe to accommodate a portion of the angular demands, less stress would be placed on the limb itself. The Seattle shoe took a radical approach to this problem and may have produced some problems of its own. If we take a more moderate approach we may reap benefits for the horse with fewer complications. Having the ground surface of the shoe work with the riding surface we achieve a partial solution. If a modified shoe were to stay on top of the working surface more than a traditional shoe and by shaping the ground surface of this shoe, we allow this shoe to establish an angle with the ground when needed. This may seem subtle, but the traditional approach to shoe placement puts a metal rim on the hoof that places a perimeter load on the foot and works to stabilize the foot flat on the ground. The difference between a conventional shoe and what is essentially a rocking shoe with multiple degrees of freedom provides the horse with a greater margin before structural compromise. While we are fine-tuning the function of the shoe, factor in the medial rotation of the forefoot during the mid-stance phase, how might this detail affect the placement of a roll or rocker?

6 The benefits of this biomechanics based approach can best be seen on a marginal patient. I have had success with the application of this concept to patients with advanced low ringbone (osteoproliferative arthritis of the coffin joint), taking him from a pasture pet to a useful trail horse. If we can provide relief for a crippled horse with this approach, conceptually through limiting the dynamic challenge to the distal limb over vast numbers of strides we may positively effect on the longevity of our healthy equine athletes.

Image 4 a and b. Advanced low ringbone with an adaptive shoeing approach.

We see the benefits of minute alterations of the shoeing process on a daily basis. Incremental adjustments in the cranial portion of the shoe, through the use of a rocker or similar modification, benefit many of our patients. Changes in the surface area of a specific region of the shoe by the addition of a bar or and onion heel, allows for a subtle alteration of how the shoe works with the ground and may benefit others. By arming ourselves with a more thorough understanding of the biomechanics of the horse’s limbs we can strive for improved solutions to meet the challenges facing the equine athlete.

Parks AH. Foot balance, conformation and lameness. In: Ross MW, Dyson SJ, editors. Diagnosis and management of lameness in the horse. St. Louis (MO): Saunders; 2003. p.250-61

Back W. The role of hoof and shoeing. In: Back W, Clayton H, eitors. Equine locomotion. St. Louis (MO): Saunders; 2001. p.135-66

Davies HMS, Philip CJ, Merritt JS. Functional anatomy of the equine digit: determining function from structure. In: Floyd AE, Mansmann RA, editors, Equine podiatry. St. Louis (MO): Saunders; 2007. p.25-41

Davies HMS, Merritt JS, Thomason JJ, Biomechanics of the equine foot. In: Floyd AE, Mansmann RA, editors, Equine podiatry, St. Louis (MO): Saunders; 2007. p.42-56

Rooney JR, Functional anatomy of the equine foot. In: Floyd AE, Mansmann RA, editors, Equine podiatry, St. Louis (MO): Saunders; 2007 p. 57-73

McIlwraith CW, General pathobiology of the joint and response to injury. In: McIlwraith CW, Trotter GW, editors; Joint disease in the horse, St. Louis (MO): Saunders; 1996. p. 40-70 7

Crevier-Denoix N, Roosen C, Dardillat C, Pourcelot P, Jerbi H, Sanaa M, Denoix JM, Effects of heel and toe elevation upon the digital joint angles in the standing horse. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 74-78

Degueurce C, Chateux H, Jerbi H, Crevier-Denoix N, Pourcelot P, Audigie F, Pasqui-Boutard V, Geiger D, Denoix JM, Three-dimensional kinematics of the proximal interphalangeal joint: effects of raising the heel or toe. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 79-83

Chateux H, Degueurce C, , Jerbi H, Crevier-Denoix N, Pourcelot P, Audigie F, Pasqui-Boutard V, Denoix JM, Normal three-dimensional behavior of the metacarpophalangeal joint and the effect of uneven foot bearing. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 84-88

8 Shoeing for Soundness: Coffin Joint Function, Pathology, and Treatment Scott Morrison, DVM Rood and Riddle Equine Hospital Lexington, Kentucky

The Distal interphalangeal joint (DIP) is the major articulation on the digit. It is the center of articulation about which many structures of the distal limb act upon during locomotion. The DIP joint therefore, is considered a focal point of the digit and is a major landmark when assessing form, function and balance. The DIP joint, being the distal most joint of the limb, is most affected by assymetrical loading patterns when ambulating on uneven terrain and is also greatly influenced by foot manipulations, such as trimming and shoeing. The range of motion (ROM) is significantly higher than the proximal interphalangeal (pastern) joint. At the trot the ROM of the coffin joint has been shown to be 47 +/- 4 degrees and the pastern joint 14 +/- 4 degrees.

The DIP joint is comprised of the articulations of the distal phalanx, distal end of the middle phalanx and the two articular surfaces of the navicular bone. (fig 1, Image from: Christoph Von Horst (www.plastinate.com) and fig 2)

Figure 1

The joint is stabilized by soft tissue structures: The common digital extensor tendon acts to extend the DIP joint, itcourses down the dorsal pastern, combines with the extensor branches of the suspensory ligament and inserts on to the extensor processof the distal phalanx. (fig 3) The extensor tendon has muliple attachments to the dorsal pastern and is adhered to the joint capsules of the pastern and DIP joint, and the ungual cartilages. Extensor tendon act to stabilze the dorsal aspect of the joint and prevents dorsal 9 luxation of the joint. The palmar aspect of the joint is stabilized largely by the deep digital flexor tendon (fig 4) and the impar ligament which originates on the distal end of the navicular bone and inserts on the distal phalanx just proximal to the DDFT insertion on the semilunar crest and the suspensory ligaments of the navicular bone (fig 6). The lateral and medial aspects of the joint are stabilized primaririly by the collateral ligaments (fig 5), Chondrocoronal (attach collateral ligament to ungual cartilage). The joint capsule assists in stablizing the entire joint.

Figure 2

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Figure 4

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Figure 6

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The DIP joint is primarily designed to move in flexion and extension, however there are rotational/transverse plane and collateral /frontal plane movements as well. These planes of motion allow the joint to tolerate uneven ground surfaces and have a range and loading rate limitations. It is believed that excessive rotational and collateromotion are the cause of excessive wear and tear on the articular surfaces.

Joints have a limited and slow rate of repair. When joint damage accumulates and out paces the repair process, clinical manifestations of joint disease arise. Gross and histological changes in osteoarthritis include: cartilage degeneration, subchondral bone sclerosis, osteophytes, synovial inflammation and periarticular fibrosis. Figure 7 shows a normal DIP joint on the left and an abnormal joint on the right, with cartilage erosions, inflamed and thickened joint capsule.

Figure 7

Damage to the DIP joint can be caused by an acute injury to the joint or peri-articular supporting structures or can be from chronic wear and tear. Degrees of lameness can be variable depending on the nature and extent of the damage. Cases present with variable degrees of sensitivity over the frog region. Distension of the joint can usually be detected by palpation of the dorsal pouch just proximal to the coronary band. Palpable joint distension is not pathognomonic for DIP joint disease. Joint distension can occur secondary to any cause of foot inflammation. It is common to detect joint distension with foot abscesses, fractures, soft tissue injuries and severe bruising. Cases typically have a positive response to lower limb flexion and are worse on hard surfaces. Diagnostic analgesia is required to accurately diagnose the DIP joint as a source of pain. The DIP joint blocks out with a PDN block (along with most of the structures of the foot). Intrasynovial analgesia of the DIP joint will desensitize the joint, but over time will also desensitize the navicular apparatus and toe region of sole. It is believed that a positive response to DIP joint analgesia within 5-10 minute is most likely the joint. After 10 minutes diffusion of anesthetic will begin to desensitize other structures. Navicular bursa analgesia is difficult to perform in some cases, but is fairly specific for desensitizing the navicular apparatus without desensitizing the DIP joint, therefore a negative response to navicular bursa analgesia and a positive response to DIP joint analgesia is a strong indication that the DIP joint is the source of pain. Radiographs in acute cases rarely will show much. In chronic cases osteophyes, narrowed joint spaces, subchondral sclerosis and enlarged synovial invaginations on distal border of navicular bone are all signs of joint disease. MRI is very helpful in evaluating the extent of the cartilage damage and peri-artular structures. MRI is also helpful in determining active inflammation and physiology of the adjacent bone.

Treatment of coffin joint disease involves managing the inflammation and its destructive action on the cartilage. Systemic and intra-articular anti-inflammatories, Hyaluronic acid and PGAGs are used. Acute 13 conditions require rest and rehabilitation whereas chronic conditions require a more long-term management program. Severe cases may require a decrease in performance level or retirement. Systemic or articular treatments with steroids, HA and PGAGs, have been shown to be of clinical benefit in decreasing inflammation and maintaining joint health. Special attention to trimming and shoeing is most likely to have the biggest impact, especially in cases with poor conformation or foot balance issues. Trimming to establish even loading medial to lateral is the goal. Radiographs should be used in cases with a history of DIP disease, to help establish a balanced trim. Trimming perpendicular to the long axis of the pastern is recommended when radiographs are not available. When shoeing, preserving the natural function of the foot is the goal. Taking into consideration the shock absorbing mechanism and loading characteristics of a healthy barefoot. There are many types of materials and styles of shoes to choose from. The ground surface and the discipline of the horse dictate what type of shoe is most appropriate. For example too much or too little traction can be damaging to the joint and supporting structures. Shoes should be fit appropriately to provide adequate support and protection, without creating unnecessary leverage and torque. The center of the DIP joint should line up to the center of the weight-bearing surface of the shoe. Depending on the degree of pathology other shoe modifications are helpful such as ease of break-over, shock absorbing pads (figure 8)and arch support. Cases of DIP joint typically do not respond well to heel elevation. Studies show that elevating the heels increases pressure in the DIP joint. Roller motion shoes and a flat pad with soft arch support in my opinion have had the most positive effect on these cases (figure 9). Roller motion shoes have a rolled heel and rolled toe, the mechanics of this shoe is believed to decrease the “jarring” at initial ground contact, and decrease resistance to rollover or break- over, thereby decreases the moment arm about the DIP joint, and decreasing stress on the joint and peri- articular structures.

Figure 8

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Synthetic shoes are available which allow for more flexibility in the shoe compared to metal shoes. When appropriately applied these shoes may mimic the barefoot condition more closely while also allowing for protection. If a case needs support for faulty conformation or for a damaged ligament for example, then a metal shoe is probably the best choice as most synthetic shoes are designed to move and flex, and lack the structural rigidity required for support.

There are many shoes, sole support materials and pads available, every case has very specific needs, evaluating the entire horse, its environment/footing, discipline, pathology and conformation are necessary to recommend the most appropriate shoeing regime for each case.

15 Applied Anatomy of the Equine Foot Mike Savoldi Director, Equine Research Center Shandon, California

As farriers we are asked to consider the following: the condition of the animal's feet, what the animal does for a living, the animal's age, how it is housed and pastured (moisture conditions and the terrain), the owner's financial reality (often different from what we are led to believe), our safety while working, the safety of others, the animal's temperament, and too many other factors to list here.

Our industry is changing quickly. More is being demanded of each of us. We are being asked to play a much more educated role in equine management and to think more scientifically. We have begun the process of looking at the equine hoof from the inside out: examining the internal structures to better understand how what we do affects the animal. Everything that happens inside the hoof is somehow reflected on the outside, but an understanding of the internal workings is critical to properly interpreting the exterior of the hoof.

My work over the past thirty-five plus years has been focused on taking apart and examining the internal structures of the equine hoof in an effort to understand and explain how what we as farriers do affects the internal workings of the hoof and over-all equine health and performance. I have dissected and studied hundreds of hoofs taken from cadavers. With each new dissection my understanding deepens. I have come to respect that no two hoofs are the same and that each one has something new to teach me. Understanding the internal structures of the hoof will enable you to approach your work with a new sense of confidence.

I have developed a method of reading the exterior of the hoof that will help you better understand what is happening within the hoof capsule. I encourage you to take any opportunity presented to examine firsthand the inner workings of this marvelous machine that is the focus of our practice: no words or system can substitute for hands-on experience as we all know. Note of warning: A little knowledge can be dangerous: take your time, go slowly, apply this gradually!

The Sole Plane & Uniform Sole Thickness: UST

For a moment I will ask you to put aside some of what you believe about what we as farriers are supposed to be accomplishing and entertain a simple concept. Forget that we are asked to "correct," "improve," and create symmetry in the equine hoof: that if a foot is not pointing straight ahead our job is to straighten it out or take a bad foot and make it better with a specialty shoe. Let me suggest that as farriers we should have only two tasks: to properly align the bone column of the leg and to protect the hoof.

The better you align the bone column, the easier it becomes to protect the hoof, shape your shoes, keep your horses (and your clients) sound and happy. This article does not deal with shoeing because the most well-made, well-fit shoe is useless if the bone column is not properly aligned.

There is only one way we as farriers are able to align the bone column: by properly orienting the Distal Phalanx (PIII) in relation to the ground surface. The orientation of PIII is established by the hoof capsule,

16 and the orientation of the hoof capsule is established by the farrier. To optimize the orientation of PIII I am suggesting a trimming protocol based on the identification of the plane established by the junction of the moist, dense sole and the White Line. We refer to this protocol as: "trimming to UST or Uniform Sole Thickness."

The hard epidermal structure of the sole will appear in the form of moist, dense, waxy tissue on the underside of the hoof. The point at which the sole begins to exfoliate is the juncture of the inside and the outside of the hoof. At this point the moist inside becomes dry and begins to exfoliate. This junction is sometimes referred to as "the moisture line". This layer of tissue establishes the "Sole Plane." The Sole Body refers to the area of the sole that forms the arch of the foot.

Although this layer of tissue reflects the outside of the hoof, it is in some sense the outer-most layer of the inside of the hoof. Properly understood, it provides us a window into the internal workings of the hoof capsule. Our goal is to learn to read the Sole Plane and to understand how it reflects the structures within. The Sole Plane should always establish the angles that are the basis for our trim.

Note of warning: an all-too-common problem is a farrier's ability to correctly identify the level of the Sole Plane in the front part of the hoof capsule: very often removing more sole in this area than is called for. The area that most of us need to focus on in incorporating these ideas is learning to identify the Sole Plane in the back half of the hoof capsule. Often, the heel area is trimmed leaving excessive length, thus creating a condition similar to that of having a wedge under the hoof as described below.

The internal workings of the hoof: an analogy

Imagine if you will, that you are standing barefoot on a small, rubber ball placed beneath the arch of your foot. Your foot, your leg and your entire body is supported on the rubber ball. As you stand, both your heel and your toes reach down to the ground to establish the base on which you stand and from which you are able to move. As you more forward, you roll over the ball and your weight descends onto your toes. As you move to one side your foot rolls over the ball and your weight is received by the side of your foot in the direction you are heading. Pretty simple?

In healthy feet, the arch serves much the same function as the rubber ball in this analogy: the arch supports your body weight and enables you to shift from front to back and side to side serving as a fulcrum around which you take each step. With each step your foot expands as the weight of your body descends towards the ground absorbing shock and taking in information about the ground surface, sending messages through the nervous system to your brain that enable you understand the terrain. Your foot, like that of horses, works in 3-dimensions: enabling you to have mobility under varied conditions, over different terrains, in different directions and at various speeds. A pretty amazing system if you stop to think about it.

Now imagine that someone places a small wedge under your foot so that the ball under your arch, your heel and your toes are all at an angle to the ground. You are no longer stable, but even as you stand still you are required to work to maintain your balance. Your body weight will pull you toward the lower side of the wedge. Your own weight will cause you to tend to roll over the rubber ball that now tends to roll towards the lower side of the wedge. If the wedge faces front, the ball will tend to roll toward the front. If the wedge faces the inside of your body the ball and your body weight will gravitate in that direction. To

17 compensate muscles in your foot, your entire leg and torso must become engaged. The steeper the wedge, the more your muscular system must compensate: working just to stand still in one place.

When you begin to move the affect of the wedge on your balance becomes more pronounced. If you try to run, all the muscles of your foot and leg must engage to compensate for imbalance caused by the wedge each time your foot strikes the ground. The joints of your foot and leg are out of alignment so your nervous system sends signals to the muscular system in an attempt to align the joint and the bones with each successive step you take. The joints will tend to incur additional stress. The skin on part of your foot which strikes the ground first will undergo increased wear and tear: from the outside in and from the inside out. The bones of your feet will over time quickly begin to change and remodel based on the unbalanced forces put upon them. Even the vascular system is affected: having to work harder to pump blood under the increased pressure from the extra engagement of the muscles and through arteries and veins constricted by this imbalance.

In this analogy, the presence of the wedge translates to trimming a hoof other than to the angles dictated by the Sole Plane. Imbalance determined by farrier trim or by the animal's confirmation causes pathology to PIII and the structures of the hoof which can cause discomfort, lead to disease, inhibit optimal performance and ultimately lead to hoof failure. We cannot correct confirmation, but by basing our trim on the Sole Plane we are aligning the hoof capsule and determining the relationship of PIII to the ground surface such that bone column is aligned optimally doing the best thing for the animal.

An understanding of UST will help you best care for a foot, whether or not the animal has good confirmation. Even when a foot is irregular or deformed as a result of pathology or injury: trimming to angles dictated by the Sole Plane is optimal. Our goal is always to establish the orientation of the hoof capsule horizontal to the ground surface as defined by the Sole Plane.

PIII and the Sole Plane

In a normally functioning hoof PIII is perched on the arches, supported by the internal structures within the hoof capsule. For purposes of this discussion we will refer to the internal structures as the "Arches" of the hoof. These structures are not solid, but essentially liquid in nature: they are malleable. They change based on the forces acting upon them. The nature of these changes affects the orientation and relationship of PIII to these internal structures within the hoof capsule and to the ground surface.

The Sole Plane vs. Uniform Sole Thickness (UST)

Trimming to Uniform Sole Thickness (UST) is a process of identifying pathology, deformities and irregularities to the Sole Plane and establishing a trim based on these irregularities and the future direction of the hoof capsule as directed by the farrier and by the veterinarian. The angles of the trim are based on those established by the Sole Plane, however, a UST-based trim takes into account: pathology to the tissue, whether or not the foot will receive a shoe, the over-all condition of the animal, what it does for a living and the animal's age and health.

The trimming protocol we have developed to aid in properly aligning the bone column with the Sole Plane we refer to as “Trimming to Uniform Sole Thickness.” The “Uniform” in UST does not refer to the sole 18 body; it only applies to the leading edge of the sole, the sole/wall junction. This junction will have small variations in the vertical depth but is more or less of uniform thickness.

Note of warning: the following images have been trimmed following a distorted white line for illustrative purposes only. In the field, a farrier is tasked with identifying the Sole Plane, understanding the demands put on the animal during the shoeing cycle ahead, leaving enough material on the underside of the hoof capsule to protect the hoof capsule whether or not it is to receive a shoe.

Here is an example of a hoof capsule after trim. An aged horse was obtained post-mortem in California. The reason for death was unrelated to the current study. The foot has been trimmed to UST exposing a distorted foot. The trim has positioned the hoof capsule horizontal to the ground surface (at a 0 degree angle). Note that the Sole Plane is severely distorted, the Sole Plane is not flat, yet this hoof is trimmed for optimal function.

The angle of the hoof capsule, as dictated by the farrier creates the forces that act upon PIII and the structures within the hoof capsule. PIII will remodel based on these forces. As PIII changes its shape, the external structures of the hoof capsule reflect these changes: the farriers trim changes the shape of the hoof capsule.

Note of warning: the Sole Plane is not always a flat plane, but a surface which may have multiple curves and angels. When trimming a hoof flat to receive a shoe, in most situations we are trimming in a less than optimal fashion.

This hoof shows definite signs of pathology: PIII in this figure shows clear and definite changes most likely resultant from the trim. This hoof demonstrates how PIII descends below the proximal border of the white line at the junction of the sole and the hoof wall. PIII has "dropped" into the sole causing the soft tissue to wrap around the solar border and the bone to remodel.

In many feet I have examined, these pathological changes have affected not only the bones, but all the internal structures surrounding the bones: the circulatory and nervous systems, the dermis, the structures of the heel, and the entire hoof capsule. A virtual domino affect: if we set-up the angles incorrectly, all the other structures of the hoof attempt to compensate and are compromised.

It has been difficult to come to the realization, but it has become clear to me in the process of dissecting many horses’ feet that the majority of hoof problems are caused by farrier misunderstanding. How we trim the hoof has an effect on all the inner workings of the hoof: the blood flow, the nervous system, even and especially the shape and interconnection of the bones and joints. When we trim a hoof such that the plane

19 of the PIII and the ground surface are not properly aligned we actually cause the bones within to begin to remodel and change their shape. Strength and consistency of the bones quickly become compromised and blood flow and the nervous system are interrupted. The bones immediately begin to remodel based on the forces we have now imposed on the system.

This hoof capsule in this final figure represents a well-functioning, healthy foot. There is little pathology to indicate distress to the structures of the hoof. The distal border of PIII is basically flat: on one plane and without distortion. Upon examination, all the internal structures of this hoof capsule appear to have been healthy.

The first stage of understanding the equine hoof is the two-dimensional relationship of the sole to the ground surface. The next step is understanding the three-dimensional structures within the hoof: the arches and the interrelationship. This understanding is at the heart of proper hoof management.

20 Biomechanics of the Stance Jeff Thomason, BA, MSc, PhD Professor, Ontario Veterinary College University of Guelph Ontario, Canada

Notes:

21 Trimming Fundamentals and Foot Pathology Mike Savoldi Director, Equine Research Center Shandon, California

Have you ever noticed the difference when you buy a new pair of boots, exactly the same as the ones you have, and try them on interchangeably with the worn-out pair? From personal experience I know that I tend to wear-out boots most on the outer heel. A brand new pair of boots, with the outside heel still intact, immediately makes my entire body feel better: I move more easily. Without thinking about it, I engage my core stomach muscles. The new shoes affect my posture, my strength and the way I move.

As farriers, we trim the horse’s feet, and when we do it correctly we make the horses move more easily, run faster and with greater ease, but if we don't...

Unhealthy feet can be devastating to the horse’s health. An incorrectly trimmed hoof can have effects on the entire health of the animal. Trimming techniques can affect stance (the position of both body and feet), body position and attitude. A horse in discomfort, under stress will not perform optimally and be difficult to work with. Farrier science is not just about trimming a foot and nailing on a shoe. It is about hoof health: optimizing the foot for health, performance and comfort. All of these goals are best met by optimizing the relationship of the bone column to the ground surface. As farriers, we do this in one way only: by establishing the relationship of the Distal Phalanx (PIII) to the ground surface.

It is imperative that we understand the position of the Distal Phalanx (PIII) within the hoof capsule and its' relative position to the ground surface. This position is determined by the internal structures of the hoof: the various components which make up the arches of the hoof. I have developed a trimming protocol to assist with this.

Like a boat on the water PIII is suspended within the hoof capsule in a fluid state by the structures of the hoof capsule. Borrowing the terms Yaw, Pitch, and Roll from the sailing vernacular works well to describe the movement of PIII within this fluid state. The relationship of the hoof capsule to the ground surface affects the rotation of PIII. PIII shifts within the capsule around the arch.

Pitch describes the movement of PIII in anterior/posterior relationship. Roll describes the movement of PIII in medial/lateral relationship. Yaw refers to the rotation of PIII and the entire bone column around itself. For example: an incorrectly trimmed hoof capsule, trimmed such that there is unequal length of wall in the lateral heel area will cause PIII to: Pitch anteriorly and Roll medially. PIII and the entire bone column will have a resultant Yaw (rotation) around itself, causing stress throughout.

Fig A: Demonstrates how the terms Yaw, Pitch and Roll can be used to define the position of PIII within the hoof capsule. The plane of the hoof capsule is defined by a horse's confirmation but is set by the farrier with the trim. Internally the plane of PIII is set by the arch. Therefore, when we trim a hoof we are setting up a three-dimensional support structure which in turn defines the position of PIII. Pathology is caused when PIII is other than on a plane with the ground surface. When PIII is not on a plane with the ground surface the hydro-mechanical structures within the hoof capsule are disrupted. Trimming the hoof capsule such that it is planer to the ground surface optimizes the function of the hoof and gives optimal health and performance to the animal. This is true even when there is already damage to the internal structures.

22 Naturally developing pathology can be due to conformation. A horse can have a less-than-optimal confirmation such that PIII, in an optimal state is not aligned with the ground surface. This sets the hoof up such that "uneven" forces are acting upon it. Bone is constantly remodeling from the forces acting upon it. Simply put, Gravity always wins. Less than optimal conformation combined with a trimming technique that sets the hoof capsule other than planer with the ground surface can be devastating to the PIII.

Fig. B: Shows pathology to PIII and its position within the hoof capsule. The red dotted line represents the type of arch associated with the developing pathology.

In some cases the hoof capsule, either as a result of confirmation or trim will be set such that PIII is set in a forward pitch. In the example at the bottom of the slide PIII set in a backward pitch. This type of pathology is often associated with hind feet.

Figs C & D: Represent a pastern conformation with the hoof capsule trimmed planer with the ground surface. Note: the hoof capsule is trimmed such that the sole is planer to the ground surface. As farriers, this is the best we can do for this type of foot. PIII in the top image shows mild pathology. The middle and lower images represent the affects on the arch and PIII when the foot is trimmed such that there is excess wall left in the heel area. The result is an increased level of pathology. Raising the heel causes PIII to slide downward as weight descends into the sole body. When the heel is raised soft tissue under stress breaks down and PIII slides into the sole causing damage to the sole in these areas.

When viewing the foot from a medial/lateral perspective, we recognize similar pathology based on the relationship of PIII to the ground surface. If PIII is set such that is in a Roll: causing one side or another to have greater or lesser forces upon it, PIII will in-turn remodel based on those forces. This pathology will affect the shape of PIII, the shape of the hoof capsule and the shape of the sole.

In Conclusion, in a horse's foot the arch and the relationship of the bones is critical to the horse's health. Bare-footed horses have very little control as far as setting and maintaining the arch and the relationship of PIII to the ground surface. As farriers, we have the ability to determine the relationship of PIII within the hoof capsule and to arrest wear to the hoof that would otherwise set PIII in a less-than-optimal state. Learning about the internal structures of the hoof capsule: the angles of the arches that comprise the support system and the external signs of pathology will help you to better serve the horses in your care.

If and when you choose to affect changes to the hoof, be patient and remember that everything you do as a farrier, even if it is setting the hoof capsule optimally, when done too quickly can be damaging and cause the animal discomfort. Communicate with veterinarians and try to develop a method for documenting your work to keep track of how your work affects the animal. Work slowly and allow the animal to let you know what feels good. Your work will become easier and more affective. Both your horses and your owners will be grateful.

23 Physiologic vs. Pathologic I – Functional Implications for the Farrier Mark Silverman, DVM, MS Sporthorse Veterinary Services San Marcos, California

To start this discussion we all must have a working understanding of the concepts of physiologic and pathologic. For the sake of this presentation, let’s take physiologic to indicate a conformation, structure, function or stress level that is within the normal or expected range for good health. Along those same lines, let’s consider pathologic to indicate that one or more of these same features fall outside what is healthy or sustainable.

With every stride the system at the far end of the equine leg provides several critical functions. The foot provides shock absorption to protect itself and the rest of the body from some of the accelerations and impacts involved in moving about in various types of terrain. In addition the foot acts as an interface for the horse to the ground, providing traction, durability and agility. Through an intricate system of both hard and soft tissues the foot also deals with the irregular and often challenging nature of the terrain to which the horse has adapted so well.

While the rest of the musculoskeletal system takes advantage of many levers and springs to endure locomotion, the hoof must rely on a compact and almost rigid structure. Note the phrase almost rigid. This is a critical modifier. Within the protective case of the hoof capsule there is cooperation between the bones, tendons, ligaments, soft tissues and even the blood itself, that allows the foot to survive and thrive. Even the hoof capsule is cleverly structured to allow for both strength and suppleness. The hoof capsule has been described as an incomplete truncated cone.a This geometric form allows for great inherent strength while at the same time allowing for needed flexibility. The concavity of the sole in itself lends for greater strength and stability of the hoof capsule. The implementation of of concavity or arch like structure continues throughout the capsule, making for a very durable system. Once you take this intricate form and cross-link it internally to the coffin bone within, we end up with a very stable form. The gross structure of the hoof capsule is made up of microtubules and an interconnecting matrix that allows for durability, self- regeneration and protection of the internal structures. Even at the point of structural failure, the capsule will redirect the defect to avoid having sensitive internal structures violated. The geometry of the capsule allows for flexibility, durability and paradoxically, stability, while at the same time providing excellent traction in a variety of terrains.

Image 1 a-c. Showing truncated cone and concavity of sole. (Images from Dr. Hood, The Hoof Project)

Silverman, MA. The cutting-in action of the equine hoof. Unpublished research. 1983

24 The hoof capsule is made up of multiple layers. The outer most layer provides shelter in the form of moisture management, limiting moisture loss in periods of low humidity while repelling moisture in times of excess. The middle layer provides strength and flexibility through an intricate balance of microtubules and intertubular matrix. The tubules are densely populated for strength and rigidity at the outer portion of the stratum medium, while being less dense at the inner portion of the stratum medium. This change in microtubule density provides a flexibility gradient, providing a more compliant material as the interface between the bone and the horny capsule is reached. The inner layer of the hoof capsule, perhaps the most complex, provides the interface between the capsule and the bony structures of the distal limb. This inner layer, the laminae, is an intricate cooperation between the bone and the capsule. A complex tissue has evolved to join the rigid bone to the more flexible hoof capsule. This tissue serves many functions and is complex in both gross structure and physiology. The laminae, picture it as living Velcro®, is mechanically intricate with a complex blood supply and has the ability for the capsule to grow past the coffin bone within while providing a strong attachment to that same bone. If you were to sleep through most of this discussion it is critical that one concept be understood, in large part the coffin bone, and thus the weight of the horse, is largely suspended within the hoof capsule by the laminae, it is not a bone in an ‘ashtray’. The laminae, in conjunction with a complex circulatory system are responsible for damping shock waves that might otherwise damage the bony structures within the hoof.

Image 2 Dissection of the layers of the foot. (Image from The Equine Distal Limb. Jean-Marie Denoix)

An additional large concept critical to understanding the role of the hoof is the idea that the caudal portion of the hoof is designed to cope with shock and energy absorption, whereas the cranial portion of the hoof is better able to handle the rigors of wear, abrasion and durability. Many factors go into supporting this concept. The hoof wall is thicker at the toe, making it more rigid. Also, going back to the original idea of the geometric design, the incomplete portion of the truncated cone is at the back of the foot, allowing for easier deformation. A little more complex to grasp is the effect of moisture content on flexibility. As the wall grows away from its origin it contains less moisture, and is therefore less pliable and more durable. Examining the distance of the distal margin of the wall at the toe vs. that of the heel, you can appreciate

25 that the horn at the ground surface of the toe region is older and results in tougher horn than that of the heel region. Combine the more resilient nature of the heels with the relatively high moisture content of the frog, the bar structure, the digital cushion, the collateral cartilages, the distal digital scutum and the complex circulatory system and you begin to see how the caudal portion of the foot has specialized to handle extremes of repetitive compression. High speed film analysis shows that, for the average horse, there is an initial heel loading or impact spike followed by vertical loading of the entire hoof ground surface and finally, prior to heel lift, a secondary loading of the caudal portion of the hoof at maximum vertical load.

Image 2. The ‘hammock’ formed by the DDFT. ( Image from The Equine Distal Limb. Jean-Marie Denoix)

The interplay of the DDFT, the laminae and the hoof capsule is complex and lends to many of the pathologic states that we experience as hoof care professionals. The equilibrium between the stabilization of the P3 within the hoof by the laminae and the tension of the DDFT is an accepted concept. If the tension of the DDFT exceeds the tensile strength of the laminae, the balance is disturbed and pathologic changes will occur. The ability to maintain equilibrium is further complicated by factoring in the structure of the hoof capsule itself. The DDFT under tension provides a sling or a ‘hammock’ for the navicular bone and the second phalanx. As vertical load on a limb is increased the direct compressive forces acting on the caudal portion of the hoof is in part countered by this ‘hammock’. As you have with the laminae and the DDFT, there is also a balance between the DDFT and the structure of the heels. If the tension of the DDFT is too great, the heels will be under challenged and the DDFT potentially over challenged. If the DDFT is lax, the structure of the heels may become overloaded and subject to failure.

It is difficult to draw a clear line where the function of one component of the foot ends and another one takes over. Shock absorption, a major function of the foot, is managed by the hoof capsule, the soft tissue structures, the bone and the circulatory system. The bones within the hoof capsule include the third phalanx, the navicular bone and the distal portion of the second phalanx. The third phalanx lends shape, support and a joint surface for the articulation of the foot. The porous nature of the bone is essential for circulatory and hydraulic function of the foot. The navicular bone, the smallest bone in the foot, is one 26 fraught with pathology. This small bone is exposed to a variety of forces including direct compression, indirect compression, tension in multiple directions and friction. Given the magnitude of forces that are experienced by the navicular bone it is quite amazing that it survives at all. The navicular bone and it’s associated soft tissue structures are the portion of the foot that act most like the rest of the locomotor system. There are levers and tendons and ligaments that respond to the stresses of locomotion, much like what goes on in the other joints of the skeleton. Of course all this physics and mechanics goes on in a semi-rigid enclosure moving extremely rapidly and repeatedly beating itself against the ground.

Even the circulatory system cannot get away with simply providing nutrients and oxygen to the critical tissues of the foot. Blood and the vasculature are also responsible for thermoregulation between the horse and the outside environment. In extremely cold environs there are shunts that direct blood flow away from the ice and snowbound hoof to aid in conserving core temperature. Blood is sent to the cold tissues only periodically to satisfy the reduced oxygen need of the hypothermic tissues of the foot. As if this wasn’t enough to ask, the blood also acts in cooperation with the laminae, the digital cushion and the vessels and other soft tissues to make the foot either more rigid or to aid it in acting as a hydraulic shock absorber as required. As an added bonus the properly functioning foot has been said to act as an auxiliary system to the heart, helping to drive the blood back up the leg to return to core circulation as the horse moves about. As a final task, the foot is also the structure, or more accurately, the system of structures, that is responsible for adapting the horse’s limbs to the irregularities of terrain and movement. The limbs of the horse have evolved through millions of years to provide the horse with great speed and endurance while maintaining a high level of agility. In this quest for speed the limbs of the horse needed to shed mass and simplify. Lost was the ability of many smaller quadrupeds for pronation and supination of the distal limbs. The horse’s legs could only extend and flex as the animal moves, leaving the foot to cope with the horse’s adaptation to uneven terrain or lean angles when turning. The bones, ligaments and even the capsule, of the foot allow for this three dimensional movement. The interface of the distal joints, working in concert with the ligaments and tendons, is such that angular adaptations are allowed while increasing load, even asymmetrically applied, increases the stability of the joint.

Image 3. Radiographs showing the coffin joint as the focus of angular compensation.

27 Alterations that occur to the foot, whether through disease, injury, conformational irregularities or human intervention may have serious implications regarding the foots’ ability to cope with the rigors of day-to-day work. In the second section of this series we will look at some of the complications that may occur if one or more of the features critical to the function of the equine foot is altered.

Silverman, MA. The cutting-in action of the equine hoof. Unpublished research. 1983

Parks AH. Foot balance, conformation and lameness. In: Ross MW, Dyson SJ, editors. Diagnosis and management of lameness in the horse. St. Louis (MO): Saunders; 2003. p.250-61 Back W. The role of hoof and shoeing. In: Back W, Clayton H, eitors. Equine locomotion. St. Louis (MO): Saunders; 2001. p.135-66 Davies HMS, Philip CJ, Merritt JS. Functional anatomy of the equine digit: determining function from structure. In: Floyd AE, Mansmann RA, editors, Equine podiatry. St. Louis (MO): Saunders; 2007. p.25-41 Davies HMS, Merritt JS, Thomason JJ, Biomechanics of the equine foot. In: Floyd AE, Mansmann RA, editors, Equine podiatry, St. Louis (MO): Saunders; 2007. p.42-56 Hood D. The hoof project. Rooney JR, Functional anatomy of the equine foot. In: Floyd AE, Mansmann RA, editors, Equine podiatry, St. Louis (MO): Saunders; 2007 p. 57-73 McIlwraith CW, General pathobiology of the joint and response to injury. In: McIlwraith CW, Trotter GW, editors; Joint disease in the horse, St. Louis (MO): Saunders; 1996. p. 40-70 Crevier-Denoix N, Roosen C, Dardillat C, Pourcelot P, Jerbi H, Sanaa M, Denoix JM, Effects of heel and toe elevation upon the digital joint angles in the standing horse. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 74-78 Degueurce C, Chateux H, Jerbi H, Crevier-Denoix N, Pourcelot P, Audigie F, Pasqui-Boutard V, Geiger D, Denoix JM, Three-dimensional kinematics of the proximal interphalangeal joint: effects of raising the heel or toe. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 79-83 Chateux H, Degueurce C, , Jerbi H, Crevier-Denoix N, Pourcelot P, Audigie F, Pasqui-Boutard V, Denoix JM, Normal three-dimensional behavior of the metacarpophalangeal joint and the effect of uneven foot bearing. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 84-88

28 Physiologic vs. Pathlogic II – Adaptive Shoeing Concepts Mark Silverman, DVM, MS Sporthorse Veterinary Services San Marcos, California

It is often said that the equine foot is the source of about ninety percent of all equine lameness. Our caseloads may not reflect this level of foot injury as not all hoof problems are seen by the veterinarian, farrier or trimmer. The owners themselves manage much foot lameness. Yet still, problems of the foot provide for a fair share of lost riding hours and aggravation. While the foot itself is a complex system, perhaps the most complex portion of the equine locomotor system, the real reason for all of this concern is quite simple. The equine foot is the first line of defense against the rigors of the outside world.

Section one of this presentation served as a review of the workings of the equine foot. The design of the foot has evolved strategically to allow the foot to survive in a harsh environment with a high level of demand. What occurs when either the level of demand exceeds the capability of the foot or the foot itself is somehow compromised? Failure of the foot to perform its’ tasks will ultimately result in failure of the entire animal to succeed, or in the case of the wild horse, to survive.

The shoeing or trimming of the horse falling within normal physiologic parameters has developed into an art. The skilled hoof care practitioner can predict the location of the internal structures with uncanny accuracy. Trouble may occur when the anatomic or functional details of the foot fall outside of the norm. It is in these cases that we require additional input, often in the form of radiographs to better reveal the bony columns alignment and geometry. Other sources of additional data might be in the form of hoof tester results, percussion results, diagnostic blocks, MRI and nuclear scintigraphy results and detailed clinical evaluation. The most important single tool for the determination of the status of a foot along the physiologic to pathologic continuum is the clinical examination. If we don’t recognize something as outside of normal, we won’t know to look further. We will fall into the trap of addressing this troubled foot as a variation of normal and the underlying problem will continue to smolder, waiting for the day when it will become grossly obvious.

This presentation is not a treatise on how to address individual pathologies that we might encounter in practice. We will often be faced with a complex of challenges within a single foot or set of feet. A simple (or complex) set of “if, then” directions will not be useful for many problems encountered in the real world. If that were the case, a computer could successfully trim and shoe a horse. Once recognized, appropriate diagnostic testing or imaging is performed, giving us the tools that we need to fully understand the situation at hand. Let’s use a hoof with a long bridge to toe and a short bridge to heel ratio as a starting point for discussion.

29

Image 1a and 1b: A contractural deformity that has been manipulated.

Once this foot is recognized as being outside of normal variation, we continue with our clinical examination to get a better appreciation for the details of this foot. We notice compression of the growth rings at the proximal portion of the dorsal wall. In addition we see that the first 2 centimeters of the dorsal wall is very steep followed by a dorsal displacement of the wall as it progresses distally. The frog appears to be shorter than expected and deep in the palmar surface of the foot. The sole, cranial to the apex of the frog has no concavity and there is a distinctly bi-planar sole. While doing our visual inspection we also note that the growth rings of the capsule are divergent at the heels and the heels themselves are unusually tall. Hoof testing shows the patient to be sensitive at the sole, but otherwise unremarkable.

While waiting for the tech to be set-up to take radiographs we watch the horse walk and trot in hand. A short anterior phase of the stride for the leg in question is noted and there is a pronounced heel first landing pattern. Also worth noting is the rapid rotational acceleration of this foot at heel-off. Radiographs support what we already think we know, we’ve got a club footed horse on our hands. The palmar angle of the P3 is steep, the HLZ, taken at the top portion of the dorsal wall and at the middle portion of the dorsal wall is equal, but there is an increase in the HLZ as you get to the distal portion of the dorsal wall. The cranial portion of the P3 is deformed, with a lipping of the distal margin of the dorsal portion of the bone along with a curvilinear shape of the bone in general. The sole under this deformed section of the P3 is only 10mm thick. Mineralization of the collateral cartilages is quite advanced for a horse of this age and experience.

This is a 10 year old horse that has a history of soundness issues on the leg in question, so we know that we’re not going to simply make this a normal foot and make it all better. Just for added complication, the rider complains of what they feel is shoulder lameness and the veterinarian has not been successful at blocking out the lameness. At this point we can either fall into ‘shoeing the club foot mode’ or we can think through the issues that this individual presents. We’ve gathered quite a pool of information so far, now we must think our way through the issues at hand.

We have excess pressure on the cranial sole and tension trying to rotate the P3 within the hoof capsule displayed as hoof tester sensitivity and dorsal wall deformity. This stress has also lead to the compression of the dorsal growth rings, slowing growth in the affected region. This foot wants to have less of a lever at the forward portion of the hoof acting against the effect of the DDFT. We may even need to trim this foot a bit more upright for a while to relax the DDFT for a period until stresses settle down. Depending on the individual hoof we may want to reshape the dorsal wall, eliminating some of the flare. A rolled or rockered toe might also be useful to smooth the unrollment.

30 The heel strike/”shoulder lameness” combination also needs to be addressed, as this is the most noticeable to the rider. This loading pattern also leads to what many believe is added shock at the caudal foot. Lowering the heel is not appropriate with what’s going on in the cranial portion of the foot, but adding a caudal rocker, something more parallel to the base of the P3 will help to smooth out the strike pattern of this foot.

Through addressing the pathology of this foot we have taken a stepwise approach to improving the clinical picture. This is a more precise method than simply going to the truck for ‘club-foot shoe’. This approach will also help us to work towards treating the individual details of a case as opposed to a condition. Great cooperation between the veterinarian and the farrier is required to achieve success with method, but in the process a long-term direction for the individual will be established. One added benefit of this protocol is that when the inevitable treatment failure does occur, having understood each goal of the appliance applied we are better able to fine tune the protocol for improved results.

The concept of the adaptive shoeing vs. therapeutic shoeing is important when we are working to fully understand the mechanics of the conditions that we are treating. This may seem a fine point and overthought, but often we are treating conditions that are not going to heal. Many of the things that we address on a daily basis in clinical podiatry practice are conditions that are permanent factors in a patients’ life. Therapeutic shoeing implies that over time we will correct the condition, adaptive shoeing recognizes that we are working to accommodate an existing permanent condition. The person that lost a foot in an accident is not going to receive a therapeutic prosthesis, they will get an adaptive device to help them function well in day-to-day life.

The recognition of a permanent condition and the lifelong commitment to accommodating this condition is important when planning the approach to a particular patients shoeing. We are not going to repair chronic low ringbone with a shoe, nor are we going to ameliorate chronic low heel conformation, but we can optimize the shoeing of the individual to make the patient more comfortable and to minimize progressive damage to the foot. Wedging that low-heeled foot may provide temporary comfort, but over time the hoof capsule will become increasingly compromised. Our goal is to take a more comprehensive approach that will provide long-term benefit to the patient. Address all of the factors of the condition to achieve the best overall result. Is the patients’ low-heeled condition something that was created by us or does the horse have a tendon laxity issue that leads to an overloading of the hoof capsule? Attempting to determine the cause and history of a condition will be an aid in establishing prognosis and treatment plan.

31

Image 2: Chronic long toe with under run heels.

Taking a comprehensive path to treatment improves our ability to benefit the patient. By bringing us greater mechanical understanding of the facts surrounding a disease we will develop novel approaches to treatment outside of our routine applications. So many diseases are poorly understood mechanically that we often see therapeutic attempts that defy logic. Recently I had a young farrier shoeing a horse with chronic, stable laminitis using a heavy plastic pad to ‘protect’ the frog from pressure. He had understood that somehow the frog was involved in treating the disease, but had not made the mechanical leap in understanding to grasp how. While this may be an extreme example, there have been many cases where a farrier that could fine-tune a show horse to perform at high level had failed to grasp the mechanical change that occurs in the laminitic foot.

As the physicists of our field, take the time to work through the specifics of the pathology in play for a particular disease. In laminitis, for example, the balance between the normal tension of the DDFT and the strength of the laminar connections to the inside of the hoof capsule is affected. The failure or partial failure of the laminae, essentially living Velcro, allows the DDFT, while functioning normally to change the relationship between the P3 and the hoof capsule. The P3, normally at least partially suspended within the hoof capsule, is now supported by the hoof capsule from below. This is a huge change in structural design that needs to be accommodated by the farrier in conjunction with the veterinarian. Depending on the details of the case, other factors come into play. Chronic laminitis cases will have other concerns including hoof capsule distortions from the long-term change in function of the foot. More serious cases often suffer dorsal and medial compromise to circulation resulting in asymmetric growth. These chronic cases will often show slowed growth dorsally and medially, leading to a twisting of the capsule and a tendency to become high laterally in a routine shoeing cycle. The more advanced the case of laminitis, the more compromise in function the hoof suffers. Not only is the orientation of the P3 within the capsule altered, but 32 also the capsule itself is weakened and has poor ability to regenerate properly. The loss of capsular stability is an additional contributing factor to potential treatment failure.

By taking the time to appreciate the factors involved in a specific case we can come up with a more comprehensive plan for treatment. The cooperation of the veterinarian and the farrier are crucial to the success of this approach to treatment. Each care provider will need to offer his or her specialized insight to provide a holistic approach to treatment of a specific case. The veterinarian will prove valuable in providing medical insight into the case, but to not appreciate a particular hoof capsule’s ability to tolerate a specific shoe or appliance would lead to potential treatment failure. This is where the farrier’s expertise comes into play. It is often best to discuss the mechanical goal of the proposed treatment and then come to a consensus on the method to be used. This approach may be a bit more time intensive, but will ultimately provide a more thoroughly conceived treatment plan for the patient.

If we can even begin to grasp the mechanical marvel that is the equine hoof, we will begin to understand that any change, whether due to a disease process or modification that we force upon this system will in many ways compromise it’s function. As man has domesticated the horse and challenged the horse to perform new tasks we have attempted to adapt the foot to help it to endure greater stress. The more that we strive to understand the function of the foot, the greater our chances of providing the needed modifications without compromising the evolutionary changes that have made the foot so thoroughly capable.

Eliashar E. An evidence based assessment of the biomechanical effects of common shoeing and farriery techniques. Vet Clin North Am Equine Pract. 2007; 23:425-442 Moyer WA, Carter GK. Examination of the equine foot. In: Floyd AE, Mansmann RA, eds. Equine Podiatry. Philadephia, PA: W.B. Saunders, 2007;112-127 O’Grady, SE, Poupard, DE. Proper Physiologic Horseshoeing. Vet Clin North Am Equine Pract. 2003; 19:2:333-344 Parks, AH. Form and function of the Equine Digit. Vet Clin North Am Equine Pract.2003;19:2:285-296 Redden, RF.. Hoof Capsule Distortions:Understanding the Mechanisms as a Basis for Rational Management. Vet Clin North Am Equine Pract. 2003; 19:2:443-449 Parks AH. Foot balance, conformation and lameness. In: Ross MW, Dyson SJ, editors. Diagnosis and management of lameness in the horse. St. Louis (MO): Saunders; 2003. p.250-61 Back W. The role of hoof and shoeing. In: Back W, Clayton H, eitors. Equine locomotion. St. Louis (MO): Saunders; 2001. p.135-66 Davies HMS, Philip CJ, Merritt JS. Functional anatomy of the equine digit: determining function from structure. In: Floyd AE, Mansmann RA, editors, Equine podiatry. St. Louis (MO): Saunders; 2007. p.25-41 Davies HMS, Merritt JS, Thomason JJ, Biomechanics of the equine foot. In: Floyd AE, Mansmann RA, editors, Equine podiatry, St. Louis (MO): Saunders; 2007. p.42-56 Rooney JR, Functional anatomy of the equine foot. In: Floyd AE, Mansmann RA, editors, Equine podiatry, St. Louis (MO): Saunders; 2007 p. 57-73 McIlwraith CW, General pathobiology of the joint and response to injury. In: McIlwraith CW, Trotter GW, editors; Joint disease in the horse, St. Louis (MO): Saunders; 1996. p. 40-70 Crevier-Denoix N, Roosen C, Dardillat C, Pourcelot P, Jerbi H, Sanaa M, Denoix JM, Effects of heel and toe elevation upon the digital joint angles in the standing horse. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 74-78 Degueurce C, Chateux H, Jerbi H, Crevier-Denoix N, Pourcelot P, Audigie F, Pasqui-Boutard V, Geiger D, Denoix JM, Three-dimensional kinematics of the proximal interphalangeal joint: effects of raising

33 the heel or toe. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 79-83 Chateux H, Degueurce C, , Jerbi H, Crevier-Denoix N, Pourcelot P, Audigie F, Pasqui-Boutard V, Denoix JM, Normal three-dimensional behavior of the metacarpophalangeal joint and the effect of uneven foot bearing. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 84-88

34 Traction – External and Internal Factors that Affect the Biomechanics of the Stance Jeff Thomason, BA, MSc, PhD Professor, Ontario Veterinary College University of Guelph Ontario, Canada

Notes:

35 Complicated Feet, Case Studies Scott Morrison, DVM Rood and Riddle Equine Hospital Lexington, Kentucky Notes:

36 The Upright Hoof Capsule (Are Farriers Producing Club Feet) Mike Savoldi Director, Equine Research Center Shandon, California

Notes:

37 Podiatric Considerations in the Soundness Exam Mark Silverman, DVM, MS Sporthorse Veterinary Services San Marcos, California

During your visit to Virginia for this conference, if you are a lameness person or a podiatry person, you will be bludgeoned repeatedly with the comment, ‘no foot, no horse’. The tendons and ligaments are mere stabilizers and energy stores, the skeleton simply a framework, the heart and circulatory system, just a source of nutrition and climate control and everything else just an overblown support system that allows the feet to do their critical work. The intricate and complex system that is the equine foot is the center of our world and it is our duty to appreciate every detail that the foot share’s with us. Our chosen task is to help to provide the best possible circumstance, allowing the foot to perform optimally.

While the above statement is an exaggeration, it is only a little off of being the truth. Without the foot performing well the horse’s ability to function may be severely compromised. Our ability to read the hoof, to see details and detect both subtle and overt variations from normal, allows for intervention that might enable the hoof to keep performing the task of keeping the horse moving comfortably and efficiently.

It is best to begin the evaluation of the foot through a discussion with the owner or trainer of the horse to determine their concerns and what issue(s) they feel the horse has been having. It is also useful to find out about the shoeing history, shoeing cycle and details about the horse’s use and working environment. Details disclosed during this conversation may give clues to explain what you find during your physical examination.

Prior to detailed examination of the foot it is worthwhile to take a few minutes to observe the horse in hand at the walk and trot on flat, firm footing. Information regarding landing and loading patterns will be useful in later establishment of a shoeing plan. Combining data on landing and loading patterns with irregularities of wall growth and distortions can offer great insight on stresses that may lead to or be the result of pathological conditions. Compression of the dorsal growth rings combined with widely spaced growth rings at the heel, a short frog, contracted heels and an upright foot displaying a pronounced heel first landing at the trot would suggest quite a different trim approach from a similar looking foot displaying a toe first landing.

The examination of the foot is the starting point for our appreciation of the story that the hoof has to tell. Physical examination should be a thorough and repeatable process. While an individuals approach may vary, the goal is to achieve a complete picture of the hoof and it’s relationship to the distal limb in an efficient manner. The tools required are simple and readily available and include a hoof pick, hoof knife, stiff wire brush, rasp, shoeing hammer, a flexible probe and hoof testers. The process of doing an examination of the foot is complex and has several stages. With a systematic approach and practice a complete examination of the feet can be accomplished in a handful of minutes.

Following a good cleaning, the foot should be examined in the weight bearing position from the front, sides and caudal approach. A general walk around is a good starting point. Look for symmetry of the capsule, general size and shape of the hoof and the relationship to the size of the horse. Is the shape consistent with what you feel is normal for a front or hind foot? Remembering that some asymmetry is normal given the demands on the hoof. For example, the medial wall of the forefoot is likely to be a bit more upright than the lateral wall. There is also a tendency for the medial wall to be slightly more straight from toe to heel than the lateral wall. Look for mismatching of the paired front or hind feet, swelling of the coronary band, deviations of the hairline, changes in the contour of the wall both proximally to distally and 38 circumferentially, basically anything that catches your eye. As the practitioners experience grows their powers of observation will mature and seeing the abnormal will become almost second nature. Noting the symmetry of the growth rings of the hoof wall may reveal uneven stresses within the foot or underlying biomechanical factors and might suggest potential disease states. Scars or injury sites may explain hoof wall defects or reveal sites of possible future issues. Deviations from linear growth of the dorsal hoof wall may suggest previous laminar difficulties or flexural deformities. Evaluate the alignment of hoof to the bony column distal to the fetlock, (hoof-pastern axis), a broken forward axis suggests a flexural deformity of the coffin joint and may predispose to pressure problems of the cranial sole. Alternatively, a broken back hoof- pastern axis is thought o place additional stress on the navicular complex and the deep digital flexor tendon. There is room for discussion on this concept, but it is a fair starting point.

Image 1a and 1b: Distortion of the hairline and a medial flare.

The wall of the hoof, usually smooth and a bit glossy below the coronet, may show signs of being modified to eliminate a flare or dorsal dishing. If the wall is rough that may be a sign of coronary inflammation or some other dermatological condition. Focal swelling near the coronary band may indicate a maturing abscess, local trauma, underlying joint problems or even the presence of a keratoma. While on your walk- about take note of the way the patient stands. Is he standing four square, base wide on one or more feet, camped under or out or is he consistently resting a single limb? The patient’s posture may open a door to his story and suggest hoof balance, discomfort, disease or possibly even neurologic etiology. Take the time to notice the entire horse, while our focus is on the feet, there is the rest of the support system attached to the feet that may give useful insight into the problem that we are being asked to correct. The horse standing in front of you with the lateral deviation of the left hind hoof might also show you a significant lack of muscle mass the hoof the predisposing factor or merely the result of the horse straining to adapt to his circumstance? All of these potential questions might arise before we even touch or pick up the first foot. During your visual tour keep in mind that evolution was kind enough to provide us with paired structures throughout the horse. Comparing left to right may help to determine what is normal for an individual horse.

For the next step in my tour I will pick up a front foot, noting how willing the patient is to offer cooperation. Is resistance a protective mechanism suggesting pain elsewhere, was the horse not standing well and ill prepared to give up one point of support, or is he simply dense in nature? Take a moment to feel the hoof and the surrounding soft tissues prior to actually picking the foot up. The hands are very sensitive instruments, often allowing you to feel irregularities in shape, texture and temperature of the hoof that would otherwise be overlooked. Focal heat may indicate a brewing abscess, while generalized heat might indicate a laminar flare up or generalized inflammation. Swellings above the hairline, depending on the location, might indicate joint or tendon sheath effusion or the presence of advancing periarticular disease or side bone development. While you’re down there take a minute to check the intensity of the digital 39 pulses and take note on how smoothly the coronary band blends into the hoof wall, a moat just proximal to the margin of the hoof wall suggests coffin bone descent within the hoof capsule.

Once the foot is non-weight bearing carefully observe the path of flight of the foot and distal limb. Be careful not to force the path. To accomplish this you need to get down and place your head in the area of the patient’s axillary (armpit) region. Standing upright and cranking the limb laterally to sight the bottom of the foot allows you little insight into the conformation of the horse’s joints. Where is the natural break over of the hoof? Does the passively flexed distal forelimb point to the ipsilateral hind limb or does it aim across to the contralateral hind limb suggesting a rotational deformity somewhere above the metacarpus? Are the heel bulbs symmetrical or is there evidence of a medial or lateral shear heel? Is there evidence of a varus or valgus deviation of the fetlock, pastern or coffin joint? Is the hoof capsule placed squarely on the end of the bony column or is there an abaxial displacement? All of these questions can be answered during the simple act of picking up the limb and can have a profound effect on the application of a shoe.

While the hoof is in hand, check the range of motion of the distal joints in flexion, extension and rotation. Discomfort with minimal challenge to the natural range of motion might suggest injury or a chronic pathology. Now is a good time to sight the hoof to determine if the existing balance is as you might expect it to be or if there is something glaringly out of your established parameters of balance. Combine these thoughts with those established during the dynamic motion evaluation performed earlier in establishing your approach to trimming and eventual shoe application. Perform a light clean up of the sole and frog. From a veterinary perspective we are simply going to do a light paring of the sole and a clean up of overgrowth of the frog and bars to allow for improved examination of the bottom of the foot. We’re looking for signs of penetrating wounds or defects of the sole, frog and bars. Is the frog intact or eroded, is there discoloration of the sole suggesting previous bruising, what is the orientation of the tubules of the wall and bars? Using a stiff metal brush on the bottom of the hoof allows for better appreciation of the white line and sole. A light rasping may also help to better reveal the solar surfaces. Once the bottom of the hoof is well prepared look at the thickness of the wall and the white line. Any potential abnormality of the white line, whether simply a dark spot or a stretching, should be gently explored using a flexible probe. Many times a case of advanced ‘white line disease’, actually a disease of the inner stratum medium, not the white line itself, will be occult and will not be detected until there are catastrophic side effects. It is quite easy to overlook subtle signs of this condition if exploration of this region is not performed.

Taking a more global perspective, the symmetry of the hoof needs to be assessed. The normal foot is fairly symmetrical when evaluated from the center of the frog at the widest part of the foot. The base of the heels and the break over point should be about equidistant from this central point and the distance from this point to the lateral wall should be about the same as the distance to the medial wall. Pronounced deviations from this symmetry suggest a capsular distortion indicating a flaring or under running of the wall or heel(s). A hoof that is clearly narrower than it’s contralateral partner is often being underused due to some painful condition. Observing a hoof with a greater distance from the center point to the toe than from the center point to the back of the heels, especially when accompanied by a loss of sole concavity, may have undergone a loss of laminar integrity. The nature of any distortion observed may suggest a possible etiology, prompting additional inquiry as to how to best approach the shoeing protocol.

Everyone’s workflow will vary somewhat depending on the challenge at hand. As I’m usually working to clear up a performance or soundness issue I will often examine all four feet through the next stage of examination prior to getting into the actual trim, some might slide into the primary trim following the clean up stage.

Once the foot have been closely examined, the next step in my examination is the application of compression, first through firm pressure with my thumbs to determine how substantial the sole appears to 40 be and to see if there is any pain response to mild compression. Following this gentle pressure test I will perform a more detailed hoof tester examination of the foot. The protocol for hoof tester examination of the foot needs to be very methodical. The stepwise procedure should be consistent from foot to foot, assuring consistency from one foot to the next. The hoof testers that I use have a strain gauge built in to them that allows me to self-test my consistency. While I do not engage the digital sensor for every exam, it is useful to check how much pressure I actually apply during an exam to keep it reasonably constant. It’s easy to be absolutely positive that a horse is going to have an abscess or a bruise on a particular foot and to approach the compression testing with a bit more zeal that usual, thereby increasing the odds of a positive finding.

Image 2a-c. Hoof tester position for testing the heel, navicular bursa and core structures.

Test the perimeter of the hoof, starting from one heel and working around the foot to the opposite side. I will test the heel region both high and low on the wall. In the region of the bars I will test both inside of the bar to the wall and outside of the bar to the wall, trying to isolate potential positive findings with greater specificity. Testing from across the frog to the opposite wall, both medially and laterally is also a useful study. I personally find this test more useful than direct compression from the frog to the dorsal wall on most horses. Finally, I will open the testers and compress across the entire hoof, approximating the location of the navicular bone for the placement of the testers.

Any positive findings during the hoof tester examination must be repeatable. A single withdrawal response may be an anomaly due to a fly or some other distraction, while true pain at a testing sight should be repeatable over several attempts. As a final physical test, it can be useful to perform a percussion test. With a light shoeing hammer you can tap around the walls of the foot while wait bearing, both looking for a physical response and listening for a hollow sounds suggesting possible wall disease. With the hoof being held in hand you will also percuss around the bottom of the walls and on the sole and frog in an attempt to appreciate any painful response. This same test can be useful with the shoe in place, testing the nails for sensitivity.

Thorough examination of a horse’s hooves takes longer to explain than it does to actually perform the exam, once a standardized protocol is established. Many of the points mentioned are considered almost simultaneously and the workflow can be quite smooth and fluid. Over time each individual will tailor the

41 exam to their own needs and preferences enabling them to establish the data that they feel they need to perform their task at an optimal level.

While performing the examination, take into account the work of the individual horse and any special requirements that need to be met. Also keep in mind the natural differences in duties between the fore and the hind feet, along with normal variations in morphology and balance that are expected for each. By taking the time to perform a comprehensive examination of each horse’s feet prior to trim and shoe placement you will be taking a step towards shoeing the entire horse vs. shoeing the bottom of the foot. The results over time should lead to happier horse owners and horses with improved longevity and performance.

Parks AH. Foot balance, conformation and lameness. In: Ross MW, Dyson SJ, editors. Diagnosis and management of lameness in the horse. St. Louis (MO): Saunders; 2003. p.250-61 Davies HMS, Philip CJ, Merritt JS. Functional anatomy of the equine digit: determining function from structure. In: Floyd AE, Mansmann RA, editors, Equine podiatry. St. Louis (MO): Saunders; 2007. p.25-41 Davies HMS, Merritt JS, Thomason JJ, Biomechanics of the equine foot. In: Floyd AE, Mansmann RA, editors, Equine podiatry, St. Louis (MO): Saunders; 2007. p.42-56 Rooney JR, Functional anatomy of the equine foot. In: Floyd AE, Mansmann RA, editors, Equine podiatry, St. Louis (MO): Saunders; 2007 p. 57-73 Crevier-Denoix N, Roosen C, Dardillat C, Pourcelot P, Jerbi H, Sanaa M, Denoix JM, Effects of heel and toe elevation upon the digital joint angles in the standing horse. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 74-78 Degueurce C, Chateux H, Jerbi H, Crevier-Denoix N, Pourcelot P, Audigie F, Pasqui-Boutard V, Geiger D, Denoix JM, Three-dimensional kinematics of the proximal interphalangeal joint: effects of raising the heel or toe. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 79-83 Chateux H, Degueurce C, , Jerbi H, Crevier-Denoix N, Pourcelot P, Audigie F, Pasqui-Boutard V, Denoix JM, Normal three-dimensional behavior of the metacarpophalangeal joint and the effect of uneven foot bearing. In; Buchner HHF, Davies HMS, Rossdale PD, editors; Proceedings of the fourth international workshop on animal locomotion, Equine Vet J 2001; 33: 84-88

42 Footing/Movement – Limb Injuries: What the Horse Brings to the Table Jeff Thomason, BA, MSc, PhD Professor, Ontario Veterinary College University of Guelph Ontario, Canada

Notes:

43 Hoof Capsule Distortion, Parts 1 and 2 Scott Morrison, DVM Rood and Riddle Equine Hospital Lexington, Kentucky

The importance of foot shape and balance is paramount to maintaining soundness and optimal performance. Functionally adapted for speed and efficient use of energy; the foot is relatively light compared to the large mass it supports. As many of us have witnessed the foot is a common source of lameness. It has been estimated that the heel region of the foot alone accounts for more than one third of all chronic lameness in the horse. It shouldn’t be a surprise that the only region of the horse’s body in constant contact with the ground is most susceptible to trauma and injury. The foot is the part of the body that receives the initial forces generated during ground impact. A healthy foot can dampen the vibrations generated during ground impact by as much as 80-90%

There are several mechanisms in place to accommodate shock absorption 1) hoof wall, 2) lamellar interface, 3) soft tissue (joint, joint capsule, sole corium, digital cushion, tendon/ligament, bone), 4) movement of blood into and out of the foot. When the foot is loaded the elastic hoof capsule deforms, soft tissue is compressed and stretched, the elastic/pliable lamellar interface allows the bone column to displace slightly within the hoof capsule. As the foot is loaded the compression and tension within the foot squeezes the blood out of the foot and helps drive it up the limb through low resistance vascular pathways in the collateral cartilages. The structure most responsible for transmitting external shock into movement of blood, are the bars, digital cushion and collateral cartilages. It has been hypothesized, by Dr. Rooney and Dr. Bowker, as the heels impact the ground, the bars receive vibrations and force which then transmits it to the collateral cartilages, which lie just deep to the bars. The collateral cartilages are rich in vasculature and contain a pool of blood, which receives these vibrations and converts it to the movement of fluid/blood up the limb. Basically the collateral cartilage and its vasculature provide a low resistance pathway for the rapid movement of blood out of the foot during ground impact, acting as a hydraulic shock absorber. Feet which are efficient at absorbing shock , have thick, robust collateral cartilages (with abundant vasculature) and strong well developed bars.

This is one example of why Feet must have proper form to function properly. This simply means that the anatomical structures need to be of proper mass and spatial arrangement to execute the sequence of events needed to accommodate the dissipation of vibrations generated during ground impact and support the weight of the horse. For example an underrun heel, in which the bars and collateral cartilages are not lined up, probably wont absorb shock as well as a foot with well positioned heels which line up with the collateral cartilages. When a foot has proper form we say it is “balanced”.

Arches and straight lines are strong architectural shapes. Strong feet have a sole arch and straight walls. Sighting the foot from the coronary band, the walls should be straight without flares or dishes. When feet become weak and distorted the arch typically flattens and the walls bend. Hoof capsule distortion refers to misshapen/imbalanced hooves such as flares, cracks, under run, collapsed and sheared heels. All of which are a result of long-term abnormal weight distribution on the foot. Distortions affect function, and have shown to be correlated to musculoskeletal injuries and lameness.

Distortions are a result of either overloading a healthy structure, causing it to collapse or bend, or can be the result of under loading a structure, such as the case of a contracted heel on a clubfoot. In these cases heel is under loaded and the toe is overloaded, causing the heel to contract and the toe to bend or dish. Distortions can also result from disease processes, such as laminitis, where the hoof wall in the toe region is separated and flares or dishes. Fungal infections or white line disease can also cause weakening of the 44 hoof and subsequent distortion. In the case of the Thoroughbred racehorse, we have a healthy structure that is put under repetitive high loads. Speed training puts high force on the heels, which lowers the hoof angle over time. As the angle gets lower, more force is placed on the heel creating a vicious cycle that can be difficult to correct. The combination of a lighter hoof with thinner hoof wall and sole depth combined with rigorous speed training makes the thoroughbred hoof susceptible to distortions such as under-run heels, quarter cracks, crushed heels and sheared/shunted heels. The heel region of the hoof is softer and more pliable than the toe and is designed to dissipate shock. It houses such structures as the collateral cartilages, digital cushion, and an abundant vascular system, all designed to absorb shock. The toe is more rigid, designed to penetrate the ground to establish traction. Since the heel is more pliable, and hits the ground first, hoof distortions typically present here first.

Many heel problems tend to be reoccurring. This is because the primary problem has not been effectively corrected. Having knowledge of the etiology of a foot problem will help formulate a successful treatment plan to heal the condition, prevent reoccurrence, and improve the longevity and wellbeing of the horse.

One problem that is common all over the world is the reoccurring quarter crack. Quarter cracks rarely occur out of the blue. Almost always they are preceded by a hoof capsule distortion known as the shunted heel, also called a sheared or shunted heel. Shunted heels occur as one side of the heel is loaded more heavily than the other, causing it to displace upward. As the heel bulb and hoof wall in the heel and quarter regions get pushed up, the wall reaches its limitation on elasticity; and as the heel expands during loading, the wall will crack at the hairline, creating a bleeding, painful quarter crack. As long as the heel is allowed to stay in the shunted position the foot is at high risk of cracking again. Sheared heels are believed to be the result of a conformational fault that causes overloading of one region of the foot, typically the medial (inside) heel of a front foot but can be seen on hind limbs and laterally as well.

The conformation that has historically been recognized to predispose the shunted medial heels is outward rotation of the front limbs. Most horses with outward rotation don't move efficiently, and they typically interfere as well. I see many severe sheared heels in racehorses; however, I see very few with this severe outward rotation conformation. Most racehorses I see with sheared heels seem to have fairly good conformation. When I evaluate them at the walk they seem to track well, without any significant conformational problems. This led me to study these horses a little closer. Are shunted heels the result of foot imbalance from the manner in which they are trimmed? Are shunted heels the result of conformation? Since 2010, we examined 72 sheared heels and recorded the conformation of each horse with photographs. We also took radiographs of the feet from the front and side to evaluate foot balance. Of the 72 sheared heels on front feet, 70 were medial and two were lateral. Both cases with lateral sheared heels were fetlock varus. Of the 70 medial sheared heels, 60 had a combination of carpal valgus and inward rotation of the distal limb, eight had the classic outward rotation of the limb, one had fetlock valgus, and one had normal conformation (no major conformation fault).

Using the radiographs, we investigated the relationship of medial to lateral imbalance and sheared heels. We measured the vertical distance from the medial and lateral wings of the pedal bone to the ground surface on standard horizontal front views of front feet. We were able to detect a significant difference between the normaland shearedheel cases. The sheared heel feet were out of balance medial to lateral, with the medial heel being lower. (Morrison,BeasleyandMorel,unpublished data)

The most common conformation that predisposes to a sheared heel is the carpal valgus and inward rotation of the digit. This conformation is very common in well-bred Thoroughbreds and has interesting effects on the foot. The rotation usually occurs as a result of a spiral deformity of the metacarpus (cannon) or pastern bones. As the digit rotates inward, it places the medial heel bulb directly below the boney column or vertical line of force.

45 The medial heel bulb therefore receives more force, causing it to collapse inward and be shunted upward. As the medial wall is overloaded, the vessels are compressed, slowing hoof wall and sole growth on the medial regions of the foot. As medial hoof growth is slowed down and other regions of the foot maintain normal growth, the hoof becomes out of balance or low on the medial side. This in turn causes more inward rotation of the digit.

Previous studies show that if you lower the medial hoof or raise the lateral aspect of the hoof the digit rotates inward. This sets up a cycle of overload imbalance and more overload. Since we cannot change the conformation of the limb, we must address the balance and medial wall overload. In my opinion, hoof capsule distortions occur to a large extent when the horse is standing around or on stall rest. It is during this time that the foot is largely dependent on the perimeter hoof wall and its composition for support. The feet are generally cleaned out and the horse is put into a stall with straw or shavings with very little arch/sole support. Yes, most trainers pack the feet with poultice or mud to draw out inflammation and heat but these products don’t provide adequate sole support.

They spend over 20 hours a day standing on the shod foot, which suspends the sole and frog off the ground, loading the perimeter wall. The hoof then slowly and gradually distorts and the sole arch flattens. Even though the foot can accommodate large sudden impacts during exercise, it is less able to accommodate long periods of low-intensity abnormal loading.

Management of the shunted heel:

There are several effective foot management strategies to manage this problem. The first element is the trim. The hoof needs to be trimmed for balance or even sole depth beneath the pedal bone. As discussed earlier, the shunted heel case is typically lower on the shunted heel side. Therefore these feet need to be trimmed lower on the side opposite the shunted heel. The goal is to trim the foot so that the solar surface is perpendicular to the pastern. Often a “T” square can be used to help establish the proper trim. The second component of treatment is support. This can be provided in several ways. A heart-bar or stabilizer plate is a very effective way to provide frog support and to redistribute weight off of the hoof capsule. Heart-bars and stabilizer plates can be used for training and then switched to normal race plates a few days before racing. This is an effective way to rehabilitate a shunted heel and still be able to compete with normal shoes.

Many trainers do not like bar shoes such as heart-bars and stabilizer plates because it can add weight, decrease traction, and affect the overall movement; some horses will travel differently in these types of shoes. Another way to tackle the problem is the use of temporary orthotics. Orthotics are sole/arch supports custom made for each horse. The orthotic is worn only while the horse is in the stall and removed for training. Orthotics can be bandaged to the hoof with vet wrap or elastic adhesive tape. Orthotics provide arch support 20+ hours a day when support is most needed. Most feet improve with correct trimming, heartbars/stabilizer plates, or orthotics.

Shunted heel cases should be trimmed and reshod every three weeks. As the hoof grows unevenly it becomes most out of balance towards the end of the shoeing cycle, putting the foot at the most risk of injury. In fact, most quarter cracks occur towards the end of the shoeing cycle. With diligent management and special attention to the etiology and cause of sheared heels, many quarter cracks can be prevented and sheared heels improved or resolved.

The adult club foot The club foot is a result of a shortened Deep digital flexor muscular-tendinous unit. The foot must grow a high heel to accommodate the shortened DDFT. The club foot therefore overloads the toe and bone

46 column and underloads the heel region. Arthritis, sidebone, pedal osteitis of the apex of the P-3, navicular bone sclerosis, osteoarthritis, and contracted heels are common pathologies seen. These feet often have increased wall growth in the heels and slow wall growth at the toe. This is the foot’s attempt to raise the heels and unload or accommodate the pull of the deep digital flexor tendon. Since the deep digital flexor tendon is under the most tension just before heel lift off (breakover), it is this phase of the stride, which must be addressed when re-balancing the clubfoot. It has been my experience that significantly enhancing/easing breakover can allow these feet to return to a more normal appearance. Most clubfeet can achieve equal toe/heel growth and resolve the anterior dish with these simple mechanics. It is important to realize that we are not “fixing” or resolving the contracture, we are merely accommodating it with simple shoeing mechanics and allowing the foot to return to a more normal shape, with even wall growth, no dish, good anterior sole depth, and therefore be a stronger, healthier foot. High speed video and gait analysis studies are needed to better understand how these club feet respond to shoeing but it appears to me from observing these horses and talking to owners, these horses stride out and load the heels more. It is my hypothesis that they don’t have to take a “short step” to accommodate the tendon in the caudal phase of the stride. Since the breakover is eased they lengthen the caudal phase and thus take longer strides. The other possibility is that they are just more comfortable in this style shoe and change their gait for the better. So when presented with any lower limb lameness which may be secondary to the contracture, my first approach is to re-balance the club foot by trimming the heels down and moving the breakover point back beneath the anterior coronary band and shoeing with a 1-2 degree wedge or shoe without a wedge, but rocker the shoe in the middle of the shoe instead. Both techniques seem to work well. This makes the foot behave or function more like a normal foot and often times the secondary lameness resolves or greatly improves. As these feet load the heels, the heel contracture tends to improve with time and use, however, in cases with atrophied frogs and robust bars, I encourage heel spreading by thinning out the bars, unhooking the point of the heels, and loading the frog, sulci, and bars with elastic impression material These feet even benefit from building the material up slightly above the ground surface of the shoe. Almost creating a “bumper” or artificial frog. This technique helps engage the foot’s shock absorbing structures. Occasionally these horses benefit from coffin joint injections and joint supplements but shoeing is the majority of the formula.

The low heeled foot When discussing heel pain we are more familiar with its relationship to the low heeled, sloping pastern horse for obvious reasons. Just as upright feet are probably genetically related so is the low-heeled foot. I see foals and weanlings already showing subtle signs of developing a low heel (bull nose, underrun heels, etc) however most low heel problems don’t manifest themselves until the horse is put into work, carries more weight, and has its lifestyle and foot care regimen greatly altered. Some low heels are transient as in the premature or dysmature foal however most are part of the horse’s given conformation and must be appropriately managed throughout the horse’s career or life. In the low-heeled scenario we are dealing with the opposite problem as the clubfoot. This limb has a lengthened deep digital flexor tendon-muscular unit. This allows the coffin bone to carry a low angle or even a negative angle within the hoof, as the tendon does not prop up the caudal aspect of the bone as much as in a normal foot. This lower limb conformation predisposes to many diseases such as chronic heel bruising or corns, pedal osteitis of the wing of the P-3, collapsed or crushed horn tubules in the heel buttress, quarter cracks, and various tendon/ligament injuries as these structures are overloaded and poorly supported. My approach to any of these secondary problems is to rebalance the foot so it can function properly and offer sufficient support to the structures inside the hoof and further up the limb. Low heeled feet can be classified into several different categories in order to help understand and treat them effectively. The classic low-heeled foot has the long sloping shoulder and pasterns and subsequent low heels. The second type is the horse with upright pasterns, broken back hoof pastern axis and low heels. This type probably has some degree of superficial digital flexor tendon contraction which pushes the fetlock forward, thus giving the deep digital

47 flexor tendon less distance to travel (essentially giving it more lengths) thus creating a low heel. Additionally low heels can be broken down into:

1) Underrun heels in which the heels are of good structure, just migrated forward. 2) Collapsed heels in which the heels are usually underrun to some degree but also lack good structure and fail to provide support. These heels are folded over, crushed and often times have extremely thin sole depth in the heel region.

Treatment of the low heeled foot Treatment of the low-heeled foot can be difficult and problematic. In this case we are combating compressive forces in the heel region by the palmer coffin bone dropping down unlike the club foot in which we are relieving tensile forces of the tendon contracture. As the low heel develops the foot migrates further in front of the limb, thus putting more force on the heels setting up a cycle of heel overload, structural collapse and further overload. The underrun, low-heeled foot is fairly easy to manage as this foot has good depth. The heel can be trimmed back to increase the base of support. Ideally these heels should be trimmed back to the widest part of the frog. If there is not enough depth to achieve this desired heel position the shoe is fit at least to the widest part of the frog to provide support. Since these feet are elongated or stretched, the elongated toe creates a lever, which creates strain on many structures during breakover. These feet benefit from a heavy rolled toe to ease these strains and promote the formation of a more rounded foot. The crushed or collapsed heel type is notoriously difficult to treat. It is probably the most mistreated and inappropriately managed foot type. Commonly these feet are shod with over fit bar shoes and wedge pads for support of the soft tissue structures. This is okay if you are temporarily treating a soft tissue lesion but long-term indiscriminate use causes further hoof capsule damage and pain. If we artificially prop up the heel we create more laxity in the tendon and more heel compression. A proportion of horses in wedges often improve for a few months then become sore again from secondary capsule pain. This overloading of the capsule can be seen by the growth rings on the hoofwall (slowed growth at heels, increased growth at toe.) In order to rehabilitate these feet we need a plan to distribute the weight over more surface area and to decrease weight bearing on the compromised heel region. This is done with a full roller motion shoe and some form of axial support (heartbar, heel plate, sole support, onion heels). The roller motion shoe creates airspace between ground surface of the shoe and the ground at the toe and heel regions. This probably eases the heel into weight bearing during the landing phase as to not create a sudden jolt like a conventional bar shoe. The airspace may decrease some ground reaction forces at the heels (this shoe has not to my knowledge been tested on a force plate, strain gauges, etc. to fully evaluate its effects.) My clinical experience with this shoe has been extremely favorable. Low heeled feet can become rebalanced and improved by acquiring even balanced wall growth, increase sole depth in heels, and by an increase in coffin bone palmer angle. The addition of axial support is imperative for a successful outcome in these cases. This foot type has weak supporting heel structures and the frog often appears to be prolasping through the shoe. Axial support can be in the form of a heartbar, sole support materials, heel plate, onion heel, pad, and impression material. The decision to use each of these depends on the foot, environment, discipline, and pathology. An important heel structure, which often goes, unmentioned are the bars. The functional significance of these structures cannot go unmentioned. It is hypothesized that the bars not only have an important stabilizing effect on the heels but they are probably an integral part of the shock absorbing mechanism. Weak fragile feet, which commonly have secondary lameness issues often, have weak or non-existent bars, thin collateral cartilages and are therefore inefficient poor shock absorbers. Some feet can have their bar structures rehabilitated and improved. The best way of doing this is by getting feet barefoot, however this is not always possible especially in horses, which are aggressively campaigning and competing. The use of arch supports and sole supports to load the bars has “mimicked” the bare foot condition. In some instances we load the bars with onion heel shoes and improve the quality of the bars and health of the palmer part of the foot. In our practice, rehabilitation

48 of dysfunctional heel structures are most commonly done with balanced shoeing combined with heartbars, heel plates or temporary, removable orthotics.

References Thompson KN, Cheung TK, Silverman M. The effect of toe angle on tendon, ligament and hoof wall strains in vitro. J of Equine Vet Science 1993; 13:651-53.

Hood D, Taylor D, Wagner I. Effects of ground surface deformability, trimming, and shoeing no quasistatic hoof loading patterns in horses. AJVR 2001; 62 (6): 895- 900.

Dyhre-Poulsen P, Smedegaard H, Roed J, et al. Equine hoof function investigated by pressure transducers inside the hoof and accelerometers mounted on the first phalanx. Equine Vet J 1994; 26 (5): 362-66.

Barrey E. Investigation of the vertical hoof force distribution in the equine forelimb with an instrumented hoofboot. Equine Vet J 1990; 9: 35-8.

Hood D. Center of digital load during quasi-static loading. 12th Annual Bluegrass Laminitis Symposium 1998; 47-62.

Bowker R, Page B, Ovnicek G. Morphology of the hoof wall and foot of ferel (wild) horses versus that of domestic horses. 12th Annual Bluegrass Laminitis Symposium 1998; 65-72.

Bowker R. The anatomy of the ungual cartilage and digital cushion. 12th Annual Bluegrass Lamintiis Symposium 1998; 75-91.

Wilson A, McGuigan P, Pardoe C. The biomechanical effect of wedged, eggbar, and extension shoes in sound and lame horses. AAEP Proceedings 2001; 47: 339-43.

Back W, Clyaton H. (2001) The role of the hoof and shoeing. Equine Locomotion (pp. 135-63.) Toronto: W.B. Saunders

Rooney J. (1977) Foreleg Lameness. The Lame Horse (pp. 112-47.) London. A.S. Barnes and Company

49 Diagnostic Imaging of the Foot in Sound and Lame Horses Sarah M Puchalski, BSc, DVM Palm Beach Equine Clinic Wellington, Florida

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