Diseases of the foot

Introduction

A thorough examination and assessment of the equine foot forms an essential part of both the physical and lameness evaluation. Because foot problems are the most common cause of lameness in horses, the examiner must have an accurate knowledge of foot anatomy and must be willing to take a ‘hands-on’ approach to fully identify any problems the horse might be experiencing.

There are numerous causes of pain in the foot of the horse. These can be divided arbitrarily into:

1. conditions of the hoof wall and horn-producing tissues

2. conditions of the distal phalanx and

3. conditions of the heel region.

Anatomy

• The hoof capsule is comprised of tubular and intertubular keratin arranged as a laminated composite material.

• Ninety per cent of the energy imparted by foot strike is dissipated by the hoof capsule and its associated structures.

• The anatomy of the support structures within the hoof must be understood to appreciate the various sites that could cause distal limb lameness.

The hoof capsule not only provides strength but also supports the horse’s skeletal column. In the horse, the tubular hoof of the wall is composed of hard keratin and is rich in disulphide bonds, so has great physical strength. The frog and the white zone are rich in sulfhydryl groups, but poor in disulphide bonds, and therefore have lower physical strength but greater elasticity. The strength, hardness, and insolubility of keratin are due to disulphide bonds between and within the molecules.

Two types of horn are produced from the coronary band. Tubular horn arises from cells surrounding papillae (finger-like projections from the coronary band) and become organized into thin, elongated, cylinders or tubules. In cross-section, the keratinocytes of individual hoof wall tubules are arranged around a central hollow medulla in nonpigmented concentric layers. The keratinocytes generated between the papillae mature into intertubular hoof, thus forming a keratin matrix in which tubules are embedded. The intertubular horn is formed at right angles to the tubular horn and bestows on the hoof wall the unique property of a mechanically stable, multidirectional, fiber-reinforced composite.

The corium is the region of the foot that nourishes the hoof-wall cells. There are several distinct zones, the coronary corium, lamellar corium, solar corium, and frog corium. The coronary corium fills the coronary groove and blends distally with the lamellar corium. Its inner surface is attached to the extensor tendon and the cartilages of the coffin bone by the subcutaneous tissue of the coronary cushion. Collectively the coronary corium and the germinal epidermal cells that produce the hoof wall are known as the coronary band. A feature of the coronary corium is the large numbers of hair-like papillae projecting from its surface.¹

The innermost layer of the hoof wall and bars is named the stratum lamellatum after the 550–600 primary epidermal lamellae that project from its surface in parallel rows. Examination of the hoof capsule, with its contents removed, shows that the lamellae of the dorsal hoof wall are shaped like long, thin, rectangles approximately 7 mm wide and 50 mm long. One edge of the rectangle is incorporated into the tough, heavily keratinized hoof wall proper and the opposite end faces the outer surface of the coffin bone. The proximal end is curved and forms the curved shoulder of the coronary groove. The distal end merges with the sole and becomes part of the white zone visible at the ground surface of the hoof (white line).

The lamellae of the inner hoof wall are avascular and depend on capillaries in the microcirculation of the adjacent corium for nutrition. The lamellar corium covers the coffin bone. The primary function of the lamellar hoof is to suspend the coffin bone within the hoof capsule. The tips of the lamellae (both primary and secondary) all are oriented towards the distal phalanx, thus indicating the lines of tension to which the lamellar suspensory apparatus is subjected. The surface area of the equine inner hoof wall has been calculated to average 13.75 square feet (1.28 square meters). This large surface area for suspension of the coffin bone and the great compliance of the interdigitating lamellar architecture helps reduce stress and ensures even energy transfer during peak loading of the equine foot.

The supporting structures within the hoof include the collateral cartilages, digital cushion, digital extensor tendon, collateral ligaments of the distal interphalangeal joint, deep digital flexor tendon, collateral sesamoidean ligament, distal sesamoidean impar ligament.²

The collateral cartilages have considerable variation in anatomic details from horse to horse. They vary in thickness and degree of mineralization, but the heel portion is usually thinner than the more dorsal and distal portions. The cartilages are stabilized by ligaments that attach to the middle and distal phalanges, the navicular bone and to the collateral sesamoidean ligaments. A venous plexus lies on the abaxial surface of the cartilage.²

The digital cushion is an elastic tissue composed of collagen, elastin and adipose tissue. It lies between the frog and the deep digital flexor tendon at the heel of the foot and is responsible for shock absorption.²

The navicular bone is stabilized by:

1. the paired collateral sesamoidean ligaments which originate on the distal, abaxial and dorsal aspects of the first phalanx and insert on the abaxial surfaces of the second phalanx and the proximal border of the navicular bone

2. the distal sesamoidean impar ligament which originates on the distal border of the navicular bone and inserts on the flexor surface of the distal phalanx and

3. the distal extension of the deep digital flexor tendon that courses over the flexor surface of the navicular bone and inserts on the flexor surface of the distal phalanx. The distal border of the navicular bone also has synovial invaginations that contain blood vessels.²

The invaginations may be referred to as synovial channels or vascular channels and may become enlarged and irregular when navicular bone degenerative changes have occurred.

The distal interphalangeal joint shares an articulation with the dorsal surface of the navicular bone and is stabilized by collateral ligaments that originate on the distal abaxial surface of the middle phalanx and insert in the abaxial surface of the distal phalanx.² This joint has a dorsal and palmar pouch. The dorsal pouch extends proximally to the mid-portion of the middle phalanx. The palmar pouch is extensive and is closely associated with the palmar nerves, making desensitization of palmar structures of the foot with anatomic specificity problematic.^2,3 The navicular bursa lies between the deep digital flexor tendon and the flexor surface of the navicular bone and has close association with the distal interphalangeal joint.

Examination of the distal limb

Size, shape, toe length, heel length, hoof pastern axis, and position of each foot relative to each limb and to each other are assessed with the horse standing quietly.4–6 Hoof alignment is viewed from the dorsal and lateral aspect.² Most horses will have a hoof angle between 50 and 55°. Ideally, when the horse is standing square; the cannon bone, pastern, and hoof should have straight axial alignment as observed from the front. From the side, the hoof/pastern axis should be straight. The angle created by the dorsal hoof wall should be the same as the pastern angle and the heel angle should be within 5° of the toe angle.⁷ Horses that have a low hoof angle compared to the pastern have a broken-back hoof/pastern axis (Fig. 14.1). This hoof conformation is also called ‘long toe and low heel’. The opposite case is a steep hoof angle and sloping pastern which will have a broken-forward hoof/pastern axis. This hoof conformation may also be called ‘club foot’.

Fig 14.1 Long toe with underrun heels. Note how the bearing surface of the hoof and the caudal extent of the shoe is well cranial of the optimal position. Less heel stress would occur in this foot if the hoof was trimmed to bring the bars caudally and the shoe was set with its caudal aspect in line with the bulbs of the heel.

Generally, the front hoof should be round or circular in shape, whereas the rear hoof is more triangular or pear-shaped. Front and rear hooves should be shaped like inverted cones. Both hooves should be evaluated for differences in length and width. Hooves of equal width and length tend to look circular but as hoof capsule length increases the width of the hoof wall in the quarters becomes more upright and the stresses on the hoof will naturally be different. A normally balanced hoof should have a flat ground-bearing surface and the bearing surface should be perpendicular to the upper limb. The heels should be evaluated to determine if they provide sufficient support to the hoof and limb.

Observing the foot while the horse is walking will help determine the manner in which the horse lands and breaks over, as well as the path of the foot during the flight phase of the stride. Toe-first landing or excessively heel-first landing indicates either compensation for pain or dorsopalmar hoof imbalance. Similarly, medial or excessively lateral heel-quarter-first landing suggest either compensation for limb conformation or pain leading to mediolateral hoof imbalance. The flight of the foot during the stride is correlated with rotational deviation of the limb and imbalance of the foot. The horse that wings-in or ‘dishes’ is either toed-out or breaking over the inside toe. Conversely, the horse that paddles or wings-out is either toed-in or breaking over the outside toe.

Once the above observations have been made, the examiner needs to make a closer evaluation of the hoof. This evaluation needs to be performed first with the horse in weight-bearing position and then with the foot in non-weight-bearing position.

The pastern is palpated to determine if there is heat, pain, or swelling. More subtly, the examiner needs to palpate the bones and tendinous structures. The digital neurovascular bundle is palpated to evaluate the digital pulse and to determine if a neurectomy may have been perfomed. It is normal to feel a digital pulse but not a bounding pulse, which is abnormal and an indicator of foot inflammation. The strength of the pulse can be compared to other limbs if one is in doubt. A symmetrical abnormal pulse indicates generalized inflammation, whereas an asymmetric pulse indicates the inflammatory process on the side of the stronger pulse.

Palpation is continued to the coronary band. Abnormalities such as swelling, discharge, focal pain or heat, or absence of tissue (loss of sponginess or a ‘trough’) should be examined more closely. The examiner should feel that the hairline forms a smooth edge with the hoof capsule.

From the coronet, the examiner moves to the collateral cartilages where they are palpated and manipulated. The palmar and proximal edges should be easily defined. The thickness, density, and pliability of the cartilages need to be assessed. Palpation of this area will not only determine if there is any pain, but also can give an impression of the flexibility of the hoof. For instance, a very stiff inflexible collateral cartilage is associated with a narrow, upright hoof. On the other hand, flimsy cartilages are commonly seen in the hoof with collapsed heels and a narrow, convex frog.

The entire hoof wall must be examined for the presence of cracks, fissures, bulges, growth abnormalities, focal heat, wall loss, or breakage. A high percentage of quarter and heel cracks begin as small, very fine fissures at the coronet. They might extend less than 1 cm distally and are easily missed if this area is not examined carefully. These small fissures are a definite cause of foot pain and usually associated with deeper injury to the coronet and/or lamina below.

From this point it is natural to begin manipulating the foot in the non-weight-bearing position.⁴ Begin by cleaning the bottom of the hoof and lightly paring away any debris that obscures visualization of the frog, sulci of the frog, sole, and white line if the horse is unshod. The frog should be examined for size, shape, and consistency, and to determine whether it is securely attached to the underlying tissue and its sulci (collateral and central). The frog should be resilient and rubbery, rather than hard and flaky, and the caudal two-thirds should be nearly level with the ground surface of the hoof wall. The frog should not be recessed deep into the sulci of the foot and nor should the frog be convex at its apex. The receded frog is often associated with upright narrow feet, whereas the convex frog is associated with weak and underrun heels.

The entire sole of the foot should be carefully examined for condition of the bars, fissures, punctures, consistency, discoloration (bruising), and the degree of concavity. The shape of the sole should be concave. A flat sole might signify either poor hoof conformation (a weak hoof) or distal coffin bone displacement. A convex (dropped) sole indicates a displaced coffin bone. The consistency (relative degree of stiffness) of the sole is determined using digital pressure as well as hoof testers. At this point it is necessary to evaluate the texture of the sole. By grasping the quarters with your fingers, the thumbs can be used to gently press on the sole. A sole that moves under this pressure is thin and there is little space between the coffin bone and the outside environment. On the other hand, if the sole does not move then the examiner knows there is at least some thickness and depth to the sole. True sole depth can be determined via radiography.

The white line (the junction between the sole and inner hoof capsule) is examined to determine its width and character. The white line is usually wider at the toe and gradually thins as it approaches the heels. It is best visualized following either light paring with the hoof knife or light rasping of the superficial portion of the sole margin. Hoof structures superficial to the white line are insensitive, while structures more central are considered sensitive. Widening of this area represents stress and separation of the laminar hoof wall from coronary hoof wall. The deeper the separation, the more severe the injury. This separation can be seen anywhere on the solar surface and indicates a bending force on the wall that is pulling the wall away from the coffin bone. Most frequently this separation is seen at the toe and is referred to as ‘seedy toe’ because it looks like small seeds could fit between the spaces created by the separation.

Digitally explore the heel bulbs for the presence of swelling, heat, pain, or separation at the coronet. The central sulcus of the frog should be examined and probed to determine its depth. Normally this should be a shallow depression of no more than a centimeter. If the sulcus is deeper it can be due to either very serious thrush or loss of structural support in heel bulbs (the heel bulbs can be distracted in opposite vertical directions).

Lightly support the limb at the metacarpus (metatarsus) and allow the foot to drop naturally. Position your line of vision so as to appreciate foot balance and levelness of the walls (see above). Examine the entire ground surface of the foot to determine the divisions of the hoof (toe, quarters, and heels) and their proportions (Fig. 14.2). Imagine a line drawn through the axial center of the limb, which transects the ground surface of the foot, and then determine the relative proportion of medial and lateral foot to this imaginary line. For example, a given foot may demonstrate a unilateral medial heel contraction in combination with a flared lateral quarter and toe (diagonal imbalance).

Fig 14.2 Solar surface of a foot prior to trimming. Lines have been drawn across the widest portion of the foot and sagittally. From this perspective the foot is in quite good balance. The dorsal and palmar portions of the foot are nearly equal. The half to the viewers right (lateral) is slightly larger than the half to the left (medial).

If the horse is shod, the exam should include the following additions.⁴ Note the shoe type as well as the presence or absence of additions such as toe grabs, block heels, trailers, and so forth. Determine if abnormal shoe wear exists.

Objective assessment of hoof balance

As part of the overall evaluation of the horse an objective assessment of hoof balance is important.

Examination of lateral and dorsopalmar (plantar) radiographic projections of the hoof allows objective evaluation of hoof balance. The lateral radiograph should be evaluated for middle and distal phalanx alignment, which may reveal the presence of a broken-hoof axis (Fig. 14.3). In addition, the alignment between the distal phalanx and the hoof wall should be assessed. If the hoof wall and dorsal surface of the distal phalanx are not parallel the functional hoof angle can be determined by measuring the angle of the dorsal surface of the bone with the ground. The slope of the heels can be seen on the radiograph and evaluation is used to determine whether the heels are underrun.

Fig 14.3 Lateral radiographic view of the distal limb with a broken-back hoof-pastern axis. The dorsal hoof angle (distal yellow line) has lower angle of slope than the higher angle of slope pastern (proximal dorsal line).

The dorso-palmar radiographic projection should be assessed for joint alignment, medial and lateral hoof wall lengths, and foot symmetry (Fig. 14.4). Joint alignment is determined by examining the symmetry of the joint space. The hoof wall length can be measured directly from digital images.

Fig 14.4 Dorsopalmar radiographic view of the distal limb with marked lateral-medial imbalance. The solar surface of the distal phalanx (yellow line) should be parallel to the shoe and ground surface.

Assessment of pain

Examine the horse in motion; watch the foot strike for each foot. Determine if the foot lands flat, heel or toe first, medial or lateral quarter first. The landing position of the individual foot relative to the vertical axis of the respective limb should be noted. Evaluate the path the individual foot takes from foot breakover to striking the ground. Always conduct this evaluation at the walk because this gait is sufficiently slow to permit the determination of fine movement error. Repeat the same process when viewing the horse from the side. The horse is then trotted (or paced) and visualized in the same manner. Circling the horse will often exacerbate foot problems.

Two manipulative tests should be performed: hoof tester examination and distal limb flexion. Two additional manipulations, hoof extension wedge test, and palmar hoof wedge test, may add more information.⁸ A positive response to any of these tests is important but a negative response is equivocal and does not rule out any problem. Examine the foot systematically with hoof testers. Percussion utilizing a small hammer can also provide important information regarding pain in the hoof wall or sole.

The distal limb flexion test can exacerbate lameness if any of the three distal joints of the leg are affected by synovitis or osteoarthritis. A positive response could also be expected by any condition that causes induration of the tissues of the foot. This has been shown to be positive in over 95% of horses with foot pain.⁸

The hoof extension test is performed by elevating the toe with a block, holding the opposite limb, and trotting the horse away after 60 seconds. The palmar hoof wedge test is performed by placing the block under the palmar two-thirds of the frog and forcing the horse to stand on that foot. The test can be further modified so that the wedge can be placed under either heel to determine if the pressure there causes exacerbation of the lameness.

These tests allow the examiner to evaluate the horse’s response to a particular stress. None has been shown to be pathognomonic for any particular cause of lameness.

Diagnostic analgesia

Regional analgesia will localize the region of pain. See Chapter 13 for details on local and intra-articular diagnostic anesthesia.

Imaging of the foot

After localization of the lameness to the foot imaging will be necessary to determine what pathology is present. Radiographic examination of the hoof requires a minimum of five radiographic views of each foot.⁹ The views consist of a dorso-60°-proximal to palmarodistal (D60PrPD) of the navicular bone, a dorso-45°-proximal to palmarodistal (D45PrPD) of the distal phalanx, a lateral to medial projection, a horizontal dorsopalmar projection, and a palmaroproximal to palmarodistal navicular bone projection (navicular skyline). Digital imaging is the current standard for radiography and provides more detail than analog film/screen radiography, allows for manipulation of image window and level, and permits measurement of various aspects of conformation using DICOM image software.

Many structures within the hoof may be evaluated sonographically.¹⁰ The collateral ligaments of the DIP joint can be clearly identified, as can the deep flexor insertion on the third phalanx, the distal deep flexor tendon, the impar ligament, and the navicular bursa (see Chapter 20).

The presence or absence of inflammation within the distal limb can be evaluated through the use of nuclear scintigraphy.¹¹

Magnetic resonance imaging (MRI) has increased the understanding of the inter-relationships between soft tissues, bone and cartilage within the foot. To fully determine the cause of foot lameness, MRI must be considered for a horse with lameness that resolves with distal limb diagnostic analgesia and that has few abnormalities evident on a radiographic or sonographic study of the distal limb. MRI allows for high-detail imaging in multiple planes and is a particularly sensitive technique for soft tissue evaluation.12,13 Imaging with fat suppressed MRI sequences also provides a degree of physiological understanding of the region. For example, fat suppressed MRI imaging may identify increased levels of fluid within bone, referred to as bone contusion or bone edema that cannot be identified with any other imaging technique.¹⁴

Diseases of the hoof wall

Hoof wall defects

• Lameness associated with hoof wall defects is due to irritation of the sensitive lamellae due to exposure, local infection or shearing of the unstable hoof capsule.

• Treatment should clean and stabilize the defect to permit healing from the coronary band.

• Healing of defects may require 5–10 months.

Recognition

Treatment and prognosis

Therapeutic aims

The first objective and most important goal of treatment is to eliminate or correct the problem that caused the hoof defect. If the underlying problem is not corrected recurrence should be expected.

Initial treatment is done to either stabilize a defect or prevent its further extension in the hoof capsule. Debridement of the defect is necessary to remove contamination of the hoof capsule and deeper laminae. Long-term support or protection of the affected region must be made, usually with appropriate shoeing and hoof capsule stabilization.

Therapy

Healing of these injuries is based on growth of new horn from the coronary band. These tissues do not heal side to side; therefore healing is slow, and may take 5–10 months. The defect must be stabilized to prevent the crack from expanding. This can be accomplished by application of a bar shoe that relieves pressure on the affected wall. The bar may be a full bar or a diagonal bar. Also, if the crack is near the heel, weight bearing to the heel can be reduced by floating the heel (Fig. 14.5). The affected heel is trimmed short enough to prevent contact with the shoe during weight bearing. The objective is to relieve shear forces across the defect, which may cause movement at the area of the crack. In addition, clips placed on either side of the defect will help prevent hoof expansion and, therefore, will further immobilize the crack. The crack may also be sutured or wired. In some cases a small metal plate can be screwed into the wall over the crack.

Fig 14.5 Repaired hoof crack with floated heel. The hoof crack has been debrided and stabilized with hoof staples. The foot has been shod with an egg bar shoe. A quarter clip is placed immediately dorsal to the hoof crack and the affected heel has been trimmed short enough to prevent contact with the shoe (‘floated heel’).

If the hoof crack does not extend from the ground to the coronary band, changes in the hoof wall may be made to prevent crack lengthening. Grooving the hoof wall perpendicular to the defect has the effect of deflecting stress away from the crack. Cracks that originate from the weight-bearing surface should be grooved at the most proximal aspect of the crack. Cracks that originate from the coronary band should be grooved at their distal aspect and in the shape of a V. Grooving will only be effective if the crack does not extend into sensitive tissues. Acrylic repair of a crack is a cosmetic and very successful method used to obliterate the crack and provide some level of immobilization. Sealing of a contaminated crack should not be done as it may lead to a local abscess.

Because of their horizontal orientation hoof clefts do not lengthen as do cracks. However, clefts are much more likely to involve sensitive layers and cause lameness. The horn around the cleft should be removed to the depth of the cleft. Sufficient horn should be removed so there is no undermined horn. In many cases, this may require a partial resection of the hoof wall from the cleft to the weight-bearing surface; a rotary burr (Dremel tool) does an excellent job. After sufficient hoof wall is debrided, the underlying tissue should be inspected carefully.

Treatment of crumbling hoof may require wide debridement of hoof wall. As for a cleft, all undermined hoof wall should be removed. It should be removed until intact hoof wall is present around the edge of the debrided area. Again, the deep tissues must be carefully examined for necrotic tissue or contaminated debris.

Long-term support or protection of the defect is necessary to return the horse to use as soon as possible. This usually requires some type of repair to restore the integrity of the hoof wall. First, the area must be free of hemorrhage or sepsis. Controlling hemorrhage requires packing the bleeding area with gauze and wrapping the foot. Approximately one week is required to dry the hemorrhagic area and allow new horny growth over the area. Application of a 1% tincture of iodine to the horn in and around the defect will usually dry the area without desiccating it. If sepsis has occurred, or a foreign body has penetrated the hoof wall, it is necessary to soak the foot in a saturated solution of magnesium sulfate and povidone- iodine solution to eliminate the infection. It may be necessary to soak or poultice the foot for 7–10 days before the septic area is healed. An alternative to soaking is to pack the affected area with a magnesium sulfate paste or povidone-iodine ointment mixed with magnesium sulfate. This treatment is followed by application of tincture of iodine solution. A helpful hint to determine if infection is still present is to examine the area 24 h after application of iodine. The presence of moisture or exudate in or around the defect is indicative of continued active infection. Soaking should continue until the infection is resolved.

The hoof wall can be repaired after the defect has been adequately debrided and the hemorrhage/sepsis has been controlled. The hoof should be properly trimmed and balanced. In most cases, a bar shoe with clips should be applied. The hoof should be dry. Application of either acetone or alcohol to the outer layers of the horn is an excellent method to remove debris and dry the hoof. To aid retention of the repair material, the hoof wall around the defect may be beveled (undermined) for 6 mm ( inch) using a rotary hand burr. Some defects can be reinforced by wire laced across the gap. This not only helps immobilize the area but also adds substrate to which the repair material can bond. If the defect is not sutured, holes should be drilled from the normal hoof into the undermined area to allow penetration of repair material. The holes should be 0.5 to 1 cm apart.

There are numerous agents that are available for repair, including fiberglass, thin metal sheets, and acrylic/epoxy materials. The acrylic/epoxies are the most versatile materials. Modern hoof epoxies have biomechanical properties similar to normal hoof capsule, reducing the complications of hard, inflexible materials such as hoof capsule contraction. The material is mixed and applied to the defect and surrounding hoof wall. When sufficient time has elapsed to allow hardening of the material, excess acrylic is rasped away resulting in a cosmetic repair.

The horse should be re-examined at 4–8 week intervals. The shoe will need to be reset and in many cases the repair repeated until the hoof wall grows out. If the animal is active and competitive, the constant trauma may cause the repair to loosen. If the repair material loosens, it should be removed and the repair repeated.

Prognosis

The prognosis for healing of hoof wall defects is usually good to excellent. Given proper hoof care, adequate time, and proper follow-up care, the defect will heal. Large defects that have resulted from an inflammatory cause may have a tendency to recur because of damage to the laminae and loss of bonding between the hoof wall layers. However, if the hoof is kept shod and protected, further problems can be avoided.

Etiology and pathophysiology

Etiology

There are numerous causes of defects in the hoof. Careful examination of the hoof can often identify the probable cause, which must be eliminated before therapy will be effective. The first consideration is moisture; either excessive dryness or excessive moisture can result in defects. Dryness usually results in a brittle hoof that tends to crack when stressed. If the hoof is unprotected, large portions of hoof wall may break away at the weight-bearing edge. Conversely, excessive moisture can cause the hoof wall to crumble. This is probably due to a combination of a decay process caused by micro-organisms, a disruption of the normal horn tubules by the moisture, and stress on the hoof wall. This problem is usually characterized by hoof-wall crumbling, which starts at the weight-bearing surface. Examination of the wall reveals a hoof wall that is soft in nature at the area of crumbling. The hoof wall can easily be dislodged for several millimeters around the defect. The wall that is affected has little normal architecture and crumbles into a fine powder when pressure is applied.

Other contributing factors to defects include hoof conformation, balance, or improper shoe application. These problems can cause overloading of a portion of hoof wall and result in disruption of the integrity of horn. Defects resulting from speed work or work on uneven surfaces are also due to similar abnormal stresses.

Infection or foreign bodies in the hoof may also result in defects. Clefts and crumbling are the most common results of these factors. Clefts may result from either a separation of horn from the coronary band, as occurs with gravel, or from splitting of the hoof wall as a result of the inflammation associated with infection. Inflammation caused by infection disrupts the normal architecture of the hoof sufficiently to cause the wall to break or crumble under normal stress and usage.

Prevention

Prevention of hoof wall defects is best accomplished by regular farrier attention and early recognition and response to changes in hoof moisture (too dry, too wet). Hooves that are exposed to excessively moist conditions may benefit from application of sealing agents. Hooves that are extremely dry may be moisturized by simply allowing the paddock stock tank to overflow. The resulting muddy area will moisturize the hooves of horses that come to the water to drink. Horses that are in regular work and have a regular bath do not usually suffer from dry, cracked hooves. In fact, excessive hoof moisture remains a considerable problem in these horses.

Lacerations to the hoof and coronary band

• First aid should control hemorrhage and prevent further contamination.

• Damage to the corium may result in hoof wall defects.

• Deep wounds may affect synovial structures.

• Wounds that involve the hoof capsule will heal slowly by second intention.

Lacerations to the hoof causing loss of germinal tissue and either partial or complete avulsions of the hoof wall are not common injuries to the horse. When these injuries do occur, however, their management can be perplexing for the veterinarian.