History and Clinical Signs

A close nail or nail bind refers to placement of a horseshoe nail not necessarily in the sensitive structures of the hoof, but close enough that the nail exerts sufficient pressure on these structures to cause discomfort. A horseshoe nail is designed to be driven obliquely through the hoof wall. When the nail is driven, the tip is placed at the inner edge of the white line with the bevel of the nail tip facing inward. When driven, the bevel contacts the hard hoof wall and curves outward and exits 1 to 2 cm above the level of the shoe. The tip of the nail is removed and the remainder is bent over to form a clinch to hold the shoe firmly to the hoof. Correct nail placement is important because if the nail is placed too shallow (superficial), the hoof wall will weaken and possibly split; if is it placed in too far, the sensitive structures of the hoof may be entered (pricked) (Figure 28-1). Overzealous clinching of the nails causes inward bending of the nail that can result in pressure on sensitive tissues, which may result in immediate or delayed pain and lameness. Slight displacement of a shoe also can result in nail pressure on sensitive tissues.

Fig. 28-1 Schematic of ideal, close, and pricked (quickened) horseshoe nail placement.

Diagnosis

Diagnosis of nail bind is difficult and often determined by eliminating other causes of foot pain. Lameness varies from subtle to severe. Sometimes a horse exhibits a change or lack in performance. The problem may not arise until several days after shoeing. Sometimes a horse is sound when trotted in a straight line, but it shows lameness when pulled in a tight circle or when it makes a turn. It is important to realize that nail bind is not always associated with poor farriery. A good nail can become a problem nail days or weeks after shoeing if the shoe shifts, causing abnormal nail pressure, or if the horse had a poor-quality hoof wall and hoof wall loss occurs. This is a common problem in Thoroughbred (TB) racehorses and usually involves the medial heel nail (the medial quarter and heel wall usually is the thinnest aspect of the hoof wall). Hoof tester evaluation using both pressure and percussion on the outer hoof wall capsule may cause a painful response over the offending nail. Heat and increased digital pulse amplitudes may not be present, depending on the duration of the close nail. Often diagnosis is determined by pulling single nails one by one from the shoe and evaluating the horse for lameness after each nail is removed. Paradoxically, lameness is sometimes transiently accentuated after removal of the offending nail.

Treatment and Prognosis

The treatment of nail bind is removal of the offending nail; usually lameness resolves within a few days. The empty nail hole may be flushed with a disinfectant solution, such as dilute povidone-iodine solution, dimethyl sulfoxide, or an antiseptic solution such as thimerosal (Merthiolate, Eli Lilly, Chicago, United States). No additional treatment is usually needed. Prognosis is good once the nail has been removed, provided infection does not ensue.

History and Clinical Signs

Nail prick or quicking refers to penetration of the sensitive hoof structures, usually the sensitive laminae, by a driven horseshoe nail (see Figure 28-1). The horse usually reacts as the farrier drives or clinches the nail by jerking the foot from the farrier.¹ Sometimes blood appears on the nail or leaks from the nail hole. Nail pricks occur for many reasons and are not always caused by a misdirected nail. Poorly made shoes, misdirected nails, selection of a nail that is too large, poorly placed nail holes, and faulty nails can result in a nail prick. Horses with poor hoof quality, thin hoof walls, or flaring hoof walls can be very difficult to nail and thus are at greatest risk. Fractious horses and young horses that have not been previously shod may lean on the farrier or repeatedly pull the foot from the farrier, making driving a nail difficult. A rushed farrier predisposes to nail pricking, but it can also happen to the best of farriers. Damage from an improperly driven nail can vary from minimal to serious infection.

Diagnosis

Diagnosis of a misdirected nail warrants great diplomacy from the veterinarian, because many owners become unjustifiably upset with the farrier. Some horses repeatedly stomp the affected foot or paw the ground immediately after shoeing. Others point the affected limb after shoeing. Lameness may not be apparent immediately but may occur days after shoeing when the nail hole becomes infected and the trapped pus begins to exert pressure. The horse usually becomes acutely lame, and the lameness worsens over time unless it is treated. An infection may migrate up the lamellae (white line) and create an abscess or soft spot at the hairline of the coronary band. The abscess is directly aligned with the hoof wall tubules leading to the infected nail hole, which is an important diagnostic aid. Hoof tester examination, using both pressure and percussion over each nail, is essential to locate the offending nail. Increased digital pulse amplitudes and heat may be present.

Treatment

Pricks from nails can be potentially serious and require immediate treatment. If the nail prick is discovered by the farrier at the time of shoeing, the nail is removed. The nail should be examined for moisture or blood. The nail hole can be irrigated with dimethyl sulfoxide, povidone-iodine solution, or hydrogen peroxide. The nail hole is packed with iodine-soaked cotton and left open. Often the nail is redirected and no further treatment is needed. Tetanus prophylaxis is essential for an unvaccinated horse.

If the offending nail cannot be localized or the nail hole is infected, the shoe is removed. Hoof testers then are used to localize the painful nail hole. Many times the pressure from the hoof testers causes black, malodorous liquid exudate to exit from the hole. This may not be obvious immediately, but if the foot is replaced to the ground and the horse walks a few steps, exudate may become obvious. The basis of treatment is to establish drainage. The infected nail hole often requires enlargement with a loop hoof knife or curette. Ideally a cone-shaped hole is made, with the larger opening at the bottom of the hoof. The hole is irrigated or the entire foot is soaked in an Epsom salt and povidone-iodine foot bath for 20 to 30 minutes twice daily until the infection is resolved. It is important to protect the foot from the environment (mud, dirt) by keeping the foot bandaged between foot soaks. Alternatively, a poultice can be applied to the foot for several days. Additional medications usually are not necessary unless infection is widespread. Antiinflammatory medication may be beneficial to decrease pain. Once the infection has cleared, the shoe is replaced. The affected nail hole can be packed with iodine-soaked cotton, and the horse reshod with a plastic pad covering the sole. Alternately, a hole can be drilled into the shoe over the affected nail hole and the shoe can be replaced, leaving access to the infected area for daily irrigation and povidone-iodine packing.

Prognosis

Prognosis after nail prick usually is good, provided that minimal damage occurs to vital structures of the foot. Establishing drainage for infection is important to avoid potential complications, such as infectious osteitis of the distal phalanx or infection of the distal interphalangeal (DIP) joint.

History and Etiology

A bruise is a contusion or impact injury that causes focal or generalized damage with subsequent hemorrhage of the solar corium. Sole bruising occurs commonly in all types and breeds of horses, especially in racing TBs and Standardbreds (STBs).² The degree and severity of lameness vary from acute, severe lameness to chronic mild or intermittent pain, depending on location and degree of damage. It is important to determine the cause of the bruise, because this dictates proper treatment and prevention. The general cause is abnormal focal weight bearing on the solar surface of the foot. The location of the bruise is helpful in determining the cause of the injury. The most common location is the junction between the bars and the walls at the heel, termed a corn.³ Corns occur most frequently on the medial side of the front feet. Heel bruising may be the result of improper shoeing or trimming. Some farriers bend the medial branch of the shoe toward the frog to prevent the horse from stepping on and pulling the shoe. This shoe position causes direct pressure to the sole at the heel angle, instead of the heel wall, resulting in continued concussion and bruising. A shoe that is too small or does not extend far enough back under the heel can lead to heel bruising.⁴ The ends of the shoe should extend to the widest aspect of the frog for proper heel protection. Horses with long-toe–low-heel hoof conformation are susceptible to heel bruising. Toe bruising can be caused by excessive impact or weight bearing on the toe region secondary to another cause such as heel pain. An improperly positioned horseshoe that rests on the sole instead of the hoof wall also causes toe bruising. Horses with long toes and those shod with toe grabs concentrate impact at the toe region.⁴ Sole bruising occurs often in horses with flat feet because the sole repeatedly strikes the ground surface. A flat foot can be congenital, can be created by trimming the hoof wall too short, or can be caused by excessive wall breakage at the quarters. Thin-soled horses or excessive trimming of the sole reduce the sole protection and predispose to sole bruising. Loose shoes can shift position, and improperly balanced feet cause excessive impact forces to specific regions of the foot and cause bruising.⁴ Riding on hard and rocky ground can result in stone bruises. A shod foot that has overgrown to the point where the shoe is riding on the sole is at risk of bruising.⁴

Clinical Signs

The degree of lameness from sole bruising can change daily, and lameness varies among horses. Removal of the shoe usually increases the degree of lameness. The bruising can be acute or chronic depending on the cause. Digital pulse amplitudes are increased after exercise, and careful hoof tester evaluation often reveals a focal painful response. Discoloration is common, but if the bruise is chronic or deep or if the horse’s sole is pigmented, it may be difficult to identify. Bruising often affects several feet. In most horses, lameness will improve after perineural analgesia of the palmar digital nerves. Radiological changes are rare but may include a serum pocket (fluid line) between the distal phalanx and external sole abscess. Such lesions are easier to detect with digital or computed radiography than with conventional radiography. Persistent, chronic bruising may lead to osteolytic lesions or solar margin fractures of the distal phalanx.

Treatment

Initial treatment with phenylbutazone (2.2 mg/kg bid) and soaking the feet in Epsom salts help decrease inflammation. Corrective or proper shoeing is imperative to shift the weight-bearing forces away from the damaged area of the foot. Sole paint consisting of a combination of equal parts of phenol, iodine, and formalin can be applied to toughen the solar surface. Hoof balance problems and shoeing causes, such as heel calks, toe grabs, or tucked heels, should be eliminated. One of many different shoeing techniques then is used to decrease impact and protect the bruised area. One method is use of a rim pad that is cut out over the bruised area so that the affected heel or quarter is “floated” and thus receives minimal weight-bearing forces. Another method is application of a bar shoe with a deeply concaved solar (inner) surface to stabilize the foot and alleviate any sole pressure from the shoe itself. A wide-web shoe may provide relief by covering and providing protection over a larger surface. It is important that this shoe be properly positioned on the hoof wall so that it does not increase sole pressure. Application of full pads packed with silicone or oakum may provide temporary relief by distributing weight-bearing forces over a wider area but often leads to a weakened and softer sole, causing recurrent problems.⁵

Prognosis

The prognosis is good if the inciting cause of the bruising can be corrected. Corrections may be difficult in horses with flat feet or long-toe–low-heel conformation, and such horses often have recurrent solar bruising.

Clinical Signs and Diagnosis

Lameness often is not apparent, but if present, the severity can vary. With severe thrush lameness can be obvious, but in most horses thrush is an additional finding and the primary source of pain is elsewhere. Diagnosis is based on the presence of black, malodorous discharge located most commonly within the frog sulci. The central frog sulcus often is malformed and very deep. A painful response may occur when the affected sulci are cleaned, because the degenerative process may extend to sensitive structures of the foot. If structural damage has occurred, the bulbs of the heel may move independently of each other, causing pain on manipulation.

Treatment

The predisposing cause should be identified and, if possible, removed. The horse should be moved to a clean, dry environment, and the feet should be cleaned daily. Any necrotic debris and undermined tissue are carefully debrided and cleaned using a hoof knife. Foot bandages may be necessary if the debridement is extensive. Systemic antimicrobial drugs may be necessary if deep or more proximal tissues are affected, but infection is usually managed by topical medication. Several caustic materials have been recommended, including a combination of phenol, tincture of iodine, and 10% formalin, Kopertox solution (Fort Dodge, Fort Dodge, Iowa, United States), or methylene blue. Initially, when the frog is very sensitive, the caustic materials may be too harsh and actually cause more tissue damage. We recommend to begin treatment by trying to dry the sensitive tissue with a mixture of sugar and povidone-iodine solution; make a paste consistency and apply that over the affected area until the tissue is dry and less sensitive. Once the frog begins to harden and keratinize, then the more caustic materials can be used. Others have recommended foot soaks in chlorine bleach (30 mL of bleach in 5 L of water). Corrective trimming and farriery may be necessary. If heel instability is present, a bar shoe may be necessary to stabilize the palmar aspect of the foot. Exercise is important to strengthen the palmar aspect of the foot and will naturally clean the feet.⁷ The best treatment for thrush involves prevention by educating the client on proper hoof hygiene.

Prognosis

The prognosis for horses with thrush is favorable if the cause can be identified and eliminated and if the condition is treated before extensive hoof damage has occurred.

History and Clinical Signs

Sheared heel refers to instability between the medial and lateral bulbs of the heel. Mediolateral foot imbalance may be a predisposing cause. It is frequently but not invariably associated with distortion of the hoof capsule. The medial bulb of heel often is displaced proximally, with a steep medial wall and flaring of the lateral wall (see Figure 6-3). However, instability between the bulbs of the heel can also occur in a more normally conformed foot, and distortion of the hoof capsule as previously described is not synonymous with sheared heel. It is also important to recognize that sheared heel can be present without causing lameness, although sheared heel may be a cause of lameness.

Sheared heel may be present in one or several feet and may be associated with mild to moderate lameness. Lameness is usually worst on firm or hard footing. There may be distortion of the coronary band, which usually is higher medially. There may be a deep cleft dissecting between the medial and lateral bulbs of the heel. Sheared heel may predispose to thrush.

Diagnosis

Instability of the bulbs of the heel is detected by grasping each bulb of the heel with the left and right hands and twisting each bulb in opposite directions in a shearing motion. In a normal horse the bulbs of the heel cannot be moved independently. Considerable independent motion can be associated with pain, causing lameness. However, if the lameness is severe, another coexisting cause of lameness should be considered. Lameness associated with sheared heel is removed by perineural analgesia of the palmar digital nerves.

Treatment and Prognosis

Any mediolateral or dorsopalmar foot imbalance should be corrected. The affected foot should be floated by trimming the high heel bulb shorter than the rest of the hoof wall such that it does not bear any weight. This allows the coronary band to drop down into the correct position. The foot with the floated heel bulb should be shod with a bar shoe to provide stability to the heel region. This may need to be continued for many months, and occasionally indefinitely, until some physical attachment between the heel bulbs has become established. If the hoof capsule is distorted in shape as previously described, the medial branch of the shoe should be set slightly wide to encourage the medial wall to grow down to it and prevent it from collapsing axially. Any excess flare on the lateral wall should be removed. The prognosis is generally good.

History and Clinical Signs

The white line, visible at the sole, is created by the junction of the insensitive laminae of the hoof wall and the horn of the sole. White line disease has historically been a term to describe the separation of the hoof wall from its laminar attachments. A crack or opening occurs within the white line, allowing a bacterial or fungal infection to invade the stratum medium, with proximity to the laminae causing cavities to develop between the laminae and outer hoof wall.⁸ Environmental conditions of either too much moisture (continuous wet pastures) or drought conditions producing excessively dry feet predispose to development of a crack or opening in the white line. Horses with poor-quality hoof walls that split or crack or those with chronic laminitis and a thickened or stretched white line in the toe region may develop white line disease. The term seedy toe

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