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Diagnosis and Treatment of Foot Infections
REVIEW Diagnosis and Treatment of Foot Infections Bob Agne, DVM
ABSTRACT The equine foot is a prime candidate for bacterial and fungal infections. The majority of infections are abscess based and generally are easily managed. Prolonged infections can result in chronic lameness and in severe cases they can be life threatening. A systematic approach to evaluation of the equine hoof can expedite the diagnosis and treatment of foot infections. Keywords: Horse; Hoof; Foot; Infection; White line
INTRODUCTION This article outlines the diagnosis and treatment of bacterial and fungal infections of the equine foot. Although the majority of foot infections in the horse are mild hoof abscesses that can be treated without any consequences, foot infections can often result in chronic lameness and in some severe cases they can be life-threatening. The hoof consists of specialized epithelial tissue, and bacteria and fungi can invade through defects in the sole or through cracks in the wall of the hoof. The white line around the ground surface of the hoof is particularly susceptible to invasion by bacteria and fungi, especially in the case of overgrown hoof walls. The white line may become more porous as compared with the sole, frog, or wall tissue and it provides a direct path to the sensitive tissues of the laminar and solar corium. Foot infections can also arise from the hematogenous seeding of bacteria into different regions of the foot. This is most often seen in foals. Chronically laminitic horses are particularly susceptible to invasion by bacteria and fungi through the dystrophic insensitive laminae. Additionally, the chronically laminitic foot may have vascular deficits that make it more difficult for these horses to fight infection. They are also more prone to toe cracks, which offer a pathway for bacteria and fungi to invade sensitive tissue. This article outlines the diagnosis and treatment of the following infections: submural and subsolar abscesses, penetrating hoof injuries, canker, thrush, white line disease (WLD), and keratomas (which, although not infections, are often accompanied by infection). From Rood and Riddle Equine Hospital, Lexington, KY. Reprint requests: Bob Agne, DVM, Rood and Riddle Equine Hospital, 2150 Georgetown Rd., Lexington, KY 40580. 0737-0806/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jevs.2010.07.019
510
SUBMURAL AND SUBSOLAR HOOF ABSCESS Typically, submural or subsolar abscesses present as an acute, moderate to severe lameness. They can usually be diagnosed by a physical examination and treated by opening the abscess and maintaining drainage until the infection has resolved. In cases where the abscess cannot be easily located, radiographs may help identify a gas opacity and thus the location of the abscess. Alternatively, a poultice can be used to soften the horn and allow the abscess to erupt on its own. Protecting the lesion from reinfection with a shoe or bandage is important to prevent recurrence. A systematic approach to locating foot abscesses can expedite diagnosis and treatment, as well as prevent unnecessary paring of the sole or other damage to the hoof capsule. First, observing the manner in which the horse loads the affected foot may give an indication as to where the abscess may be located. For example, when the patient walks with a toe-first landing pattern, the abscess may be located in the palmar/plantar portion of the foot. Second, a thorough palpation of the entire foot may help in locating the abscess, especially when the eruption is about to occur at the coronary band. This procedure may also help prevent the unnecessary removal of the shoe in cases where the abscess is likely to erupt from the coronary band or the heel bulb. Third, cleaning the entire hoof and performing a hoof tester examination may help in locating the abscess. With respect to the shod foot, special attention should be paid to the area around the clinches because sensitivity in this area may indicate an abscess or “close” nail, and removal of the offending nail could be curative. If no areas of potential eruption are found by palpation, removal of the shoe may be necessary. Shoe removal should be performed carefully because the process could be extremely painful. After the shoe is removed, the white line should be lightly pared and examined for tracts that may indicate the site of the abscess. This procedure, along with repeat hoof tester examination, may help in locating the abscess. Following the dark defect in the white line with a hoof knife or curette may open the abscess. Conservatively limiting the paring to the white line may help prevent the formation of a large defect in the hoof capsule while still allowing for drainage. Whenever possible, the sole should be avoided because a large defect in the sole will necessitate a special shoe or treatment plate for protection; however, paring of the sole cannot always be avoided with subsolar abscesses.
Journal of Equine Veterinary Science Vol 30, No 9 (2010)
B Agne Vol 30, No 9 (2010)
In cases where the abscess cannot be located, even after initial examination and exploration, radiographs may prove to be helpful by identifying gas opacities that are indicative of abscessation. After drainage has been established, a damp poultice should be applied until the drainage has ceased. It is essential that the abscess tract be protected against reinfection. Adequate protection may be achieved with a regular shoe when the tract is in the white line, but when the abscess tract involves the sole, a treatment-plate shoe or other type of protective shoe may be necessary. If, after allowing drainage, the lameness does not improve in 2 to 3 days and/or drainage continues beyond that time, further examination might be required. Deep structures, such as the coffin bone, collateral cartilages, or navicular structures, may be involved in such cases, and more intensive investigation and treatment might be required. Radiographs and fistulograms are helpful in determining the extent of the infection and the structures involved. In such cases, surgical debridement, local and systemic antibiotic therapy, and larval debridement therapy, may be necessary to resolve the infection.
PENETRATING HOOF INJURIES Penetrating hoof injuries can be life-threatening for the horse, particularly when the injury occurs in the palmar/ plantar aspect of the foot. Successful treatment requires early diagnosis and intensive treatment. If left untreated for more than 12 hours, the chances of return to soundness for injuries involving the deep digital flexor tendon sheath, the tendon itself, or the navicular bone and/or bursa are profoundly diminished. Initial examination should determine the extent of the injury and the structures involved. In cases where the metallic foreign object which causes the injury continues to remain in the wound, radiographs should be taken with the object in place. When the object is absent in the wound, a fistulogram of the wound tract can be performed under regional anesthesia (nerve block). Distal limb perfusion with a broad-spectrum antibiotic can be performed simultaneously. Penetrating wounds that enter through the frog are often difficult to locate. When such a wound is suspected, it is important to thoroughly pare and examine the frog and its sulci. Arthrocentesis of the coffin joint and navicular bursa can be used to determine whether these structures are involved in the injury. As is the case for all hoof infections, the treatment goals include: (1) debride any necrotic tissue; (2) establish drainage and maintain it for as long as necessary; (3) appropriate antibiotic therapy; (4) protection of the damaged area to prevent reinfection; and (5) support for the surrounding healthy tissue and the contralateral limb. Methods used
511
to achieve these goals will vary on the basis of the tissues involved and the severity of the wound.
CANKER Canker, or proliferative pododermatitis, is caused by an intracellular bacterium that causes dystrophic proliferation of the dermis, usually in the frog and heel bulb region of the foot. Although secondary infection is common, Treponema sp. have been identified in the cytoplasm of affected tissues. Lesions can range in severity from a discrete 1 cm diameter lesion to extensive involvement of the entire frog and sole region, and may even extend over the heel bulbs into the distal pastern. Diagnosis can be difficult in the early stages because the lesion is easily mistaken for exuberant granulation tissue. Canker lesions differ from granulation tissue in that cankerous tissue usually has a white or tan appearance instead of the typical pink coloration of granulation tissue. Biopsy and histologic evaluation may be helpful in identifying canker lesions. Treatment consists primarily of surgical debridement, which may have to be repeated when regions of proliferative tissue reappear. Protecting the surgical site and treatment with a topical antibiotic is also important.
THRUSH Although common and not often associated with lameness, thrush (dermatitis of the frog sulci) can become severe, cause lameness, and be difficult to treat. Usually involving the central sulcus of the frog, thrush is characterized by the appearance of a dark exudate and foul smell. When the bacterial infection invades the sensitive tissues of the frog, it can cause sensitivity and lameness. Treatment consists of debriding excessive frog tissue in the central sulcus, and topical treatment with 7% iodine or any of the several commercially-available products. Flossing the central sulcus with iodine-impregnated gauze ensures debridement of deep central sulci. When thrush is severe, it may be necessary to apply a treatment-plate shoe to prevent recontamination and still allow for daily treatment. In such cases, intramammary antibiotic paste used for treating or preventing dry-cow mastitis can also be helpful. Prevention of thrush includes regular foot care and maintaining a clean, dry environment for stabled horses. It should also be noted that thrush often occurs in horses with contracted heels and deep sulci. These characteristic are sometimes associated with heel pain and may indicate the need for further diagnostics.
WHITE LINE DISEASE WLD is a fungal infection of the insensitive laminae. It is characterized by chalky, crumbling white line around the ground surface of the hoof. The process undermines the
B Agne Vol 30, No 9 (2010)
512
wall and can extend proximally up the hoof wall. Typically, WLD does not cause lameness until the disease has disrupted the dermal-epidermal junction enough to destabilize healthy laminar attachment and cause tearing, inflammation, and displacement of the coffin bone (rotation and/ or sinking). Usually, farriers are the among the first to identify the problem. When mild, WLD can be treated by removing the damaged white line tissue and treating with a topical astringent. If the infection extends by >1 cm (half an inch) up the hoof wall, treatment entails removal of the undermined hoof wall until normal white line tissue is apparent at the perimeter of the entire lesion. It is important that the edges of the debrided region blend smoothly with healthy wall (ie, no undermined wall is left in place). Tools and instruments used to debride white line lesions should be disinfected after the procedure. In severe cases, a large area of the wall may be compromised, and therapeutic shoeing may be necessary to support the remaining healthy tissue. However, the shoeing materials should not cover the debrided region because the exposed area must remain dry and well aerated. There are several commercially available soaks that are helpful after debridement. In mild cases, these products can be used when shoes are reset or feet are trimmed.
KERATOMA Although it is neither an infection nor infectious, keratomas (benign epidermal tumors within the hoof capsule) may be a source of recurrent hoof infection. Initially, keratomas usually present as abscess tracts that can be resolved with conservative treatment, but which later then recur. Radiographs characteristically show a distinct, scalloped area of osteolysis on the distal margin of P3. The borders of the lesion are smooth, which distinguishes keratoma from osteomyelitis of P3, in which the borders of the osteolytic area are rough. Treatment consists of hoof wall resection and tumor excision. Therapeutic shoeing is often required after surgery to support the surrounding hoof capsule and protect the surgical site. Exposed sensitive laminae epithelializes and, when complete excision of the keratoma is performed, the hoof wall grows out normally; therefore, complete recovery can be expected.
FINAL THOUGHTS Foot infections in the equine population are common. When severe or left untreated, these infections can end horse-related careers and can even be life-threatening in some cases. Therefore, they should be treated promptly and aggressively.
ABSTRACT The equine foot is a prime candidate for bacterial and fungal infections. The majority of infections are abscess based and generally are easily managed. Prolonged infections can result in chronic lameness and in severe cases they can be life threatening. A systematic approach to evaluation of the equine hoof can expedite the diagnosis and treatment of foot infections. Keywords: Horse; Hoof; Foot; Infection; White line
INTRODUCTION This article outlines the diagnosis and treatment of bacterial and fungal infections of the equine foot. Although the majority of foot infections in the horse are mild hoof abscesses that can be treated without any consequences, foot infections can often result in chronic lameness and in some severe cases they can be life-threatening. The hoof consists of specialized epithelial tissue, and bacteria and fungi can invade through defects in the sole or through cracks in the wall of the hoof. The white line around the ground surface of the hoof is particularly susceptible to invasion by bacteria and fungi, especially in the case of overgrown hoof walls. The white line may become more porous as compared with the sole, frog, or wall tissue and it provides a direct path to the sensitive tissues of the laminar and solar corium. Foot infections can also arise from the hematogenous seeding of bacteria into different regions of the foot. This is most often seen in foals. Chronically laminitic horses are particularly susceptible to invasion by bacteria and fungi through the dystrophic insensitive laminae. Additionally, the chronically laminitic foot may have vascular deficits that make it more difficult for these horses to fight infection. They are also more prone to toe cracks, which offer a pathway for bacteria and fungi to invade sensitive tissue. This article outlines the diagnosis and treatment of the following infections: submural and subsolar abscesses, penetrating hoof injuries, canker, thrush, white line disease (WLD), and keratomas (which, although not infections, are often accompanied by infection). From Rood and Riddle Equine Hospital, Lexington, KY. Reprint requests: Bob Agne, DVM, Rood and Riddle Equine Hospital, 2150 Georgetown Rd., Lexington, KY 40580. 0737-0806/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jevs.2010.07.019
510
SUBMURAL AND SUBSOLAR HOOF ABSCESS Typically, submural or subsolar abscesses present as an acute, moderate to severe lameness. They can usually be diagnosed by a physical examination and treated by opening the abscess and maintaining drainage until the infection has resolved. In cases where the abscess cannot be easily located, radiographs may help identify a gas opacity and thus the location of the abscess. Alternatively, a poultice can be used to soften the horn and allow the abscess to erupt on its own. Protecting the lesion from reinfection with a shoe or bandage is important to prevent recurrence. A systematic approach to locating foot abscesses can expedite diagnosis and treatment, as well as prevent unnecessary paring of the sole or other damage to the hoof capsule. First, observing the manner in which the horse loads the affected foot may give an indication as to where the abscess may be located. For example, when the patient walks with a toe-first landing pattern, the abscess may be located in the palmar/plantar portion of the foot. Second, a thorough palpation of the entire foot may help in locating the abscess, especially when the eruption is about to occur at the coronary band. This procedure may also help prevent the unnecessary removal of the shoe in cases where the abscess is likely to erupt from the coronary band or the heel bulb. Third, cleaning the entire hoof and performing a hoof tester examination may help in locating the abscess. With respect to the shod foot, special attention should be paid to the area around the clinches because sensitivity in this area may indicate an abscess or “close” nail, and removal of the offending nail could be curative. If no areas of potential eruption are found by palpation, removal of the shoe may be necessary. Shoe removal should be performed carefully because the process could be extremely painful. After the shoe is removed, the white line should be lightly pared and examined for tracts that may indicate the site of the abscess. This procedure, along with repeat hoof tester examination, may help in locating the abscess. Following the dark defect in the white line with a hoof knife or curette may open the abscess. Conservatively limiting the paring to the white line may help prevent the formation of a large defect in the hoof capsule while still allowing for drainage. Whenever possible, the sole should be avoided because a large defect in the sole will necessitate a special shoe or treatment plate for protection; however, paring of the sole cannot always be avoided with subsolar abscesses.
Journal of Equine Veterinary Science Vol 30, No 9 (2010)
B Agne Vol 30, No 9 (2010)
In cases where the abscess cannot be located, even after initial examination and exploration, radiographs may prove to be helpful by identifying gas opacities that are indicative of abscessation. After drainage has been established, a damp poultice should be applied until the drainage has ceased. It is essential that the abscess tract be protected against reinfection. Adequate protection may be achieved with a regular shoe when the tract is in the white line, but when the abscess tract involves the sole, a treatment-plate shoe or other type of protective shoe may be necessary. If, after allowing drainage, the lameness does not improve in 2 to 3 days and/or drainage continues beyond that time, further examination might be required. Deep structures, such as the coffin bone, collateral cartilages, or navicular structures, may be involved in such cases, and more intensive investigation and treatment might be required. Radiographs and fistulograms are helpful in determining the extent of the infection and the structures involved. In such cases, surgical debridement, local and systemic antibiotic therapy, and larval debridement therapy, may be necessary to resolve the infection.
PENETRATING HOOF INJURIES Penetrating hoof injuries can be life-threatening for the horse, particularly when the injury occurs in the palmar/ plantar aspect of the foot. Successful treatment requires early diagnosis and intensive treatment. If left untreated for more than 12 hours, the chances of return to soundness for injuries involving the deep digital flexor tendon sheath, the tendon itself, or the navicular bone and/or bursa are profoundly diminished. Initial examination should determine the extent of the injury and the structures involved. In cases where the metallic foreign object which causes the injury continues to remain in the wound, radiographs should be taken with the object in place. When the object is absent in the wound, a fistulogram of the wound tract can be performed under regional anesthesia (nerve block). Distal limb perfusion with a broad-spectrum antibiotic can be performed simultaneously. Penetrating wounds that enter through the frog are often difficult to locate. When such a wound is suspected, it is important to thoroughly pare and examine the frog and its sulci. Arthrocentesis of the coffin joint and navicular bursa can be used to determine whether these structures are involved in the injury. As is the case for all hoof infections, the treatment goals include: (1) debride any necrotic tissue; (2) establish drainage and maintain it for as long as necessary; (3) appropriate antibiotic therapy; (4) protection of the damaged area to prevent reinfection; and (5) support for the surrounding healthy tissue and the contralateral limb. Methods used
511
to achieve these goals will vary on the basis of the tissues involved and the severity of the wound.
CANKER Canker, or proliferative pododermatitis, is caused by an intracellular bacterium that causes dystrophic proliferation of the dermis, usually in the frog and heel bulb region of the foot. Although secondary infection is common, Treponema sp. have been identified in the cytoplasm of affected tissues. Lesions can range in severity from a discrete 1 cm diameter lesion to extensive involvement of the entire frog and sole region, and may even extend over the heel bulbs into the distal pastern. Diagnosis can be difficult in the early stages because the lesion is easily mistaken for exuberant granulation tissue. Canker lesions differ from granulation tissue in that cankerous tissue usually has a white or tan appearance instead of the typical pink coloration of granulation tissue. Biopsy and histologic evaluation may be helpful in identifying canker lesions. Treatment consists primarily of surgical debridement, which may have to be repeated when regions of proliferative tissue reappear. Protecting the surgical site and treatment with a topical antibiotic is also important.
THRUSH Although common and not often associated with lameness, thrush (dermatitis of the frog sulci) can become severe, cause lameness, and be difficult to treat. Usually involving the central sulcus of the frog, thrush is characterized by the appearance of a dark exudate and foul smell. When the bacterial infection invades the sensitive tissues of the frog, it can cause sensitivity and lameness. Treatment consists of debriding excessive frog tissue in the central sulcus, and topical treatment with 7% iodine or any of the several commercially-available products. Flossing the central sulcus with iodine-impregnated gauze ensures debridement of deep central sulci. When thrush is severe, it may be necessary to apply a treatment-plate shoe to prevent recontamination and still allow for daily treatment. In such cases, intramammary antibiotic paste used for treating or preventing dry-cow mastitis can also be helpful. Prevention of thrush includes regular foot care and maintaining a clean, dry environment for stabled horses. It should also be noted that thrush often occurs in horses with contracted heels and deep sulci. These characteristic are sometimes associated with heel pain and may indicate the need for further diagnostics.
WHITE LINE DISEASE WLD is a fungal infection of the insensitive laminae. It is characterized by chalky, crumbling white line around the ground surface of the hoof. The process undermines the
B Agne Vol 30, No 9 (2010)
512
wall and can extend proximally up the hoof wall. Typically, WLD does not cause lameness until the disease has disrupted the dermal-epidermal junction enough to destabilize healthy laminar attachment and cause tearing, inflammation, and displacement of the coffin bone (rotation and/ or sinking). Usually, farriers are the among the first to identify the problem. When mild, WLD can be treated by removing the damaged white line tissue and treating with a topical astringent. If the infection extends by >1 cm (half an inch) up the hoof wall, treatment entails removal of the undermined hoof wall until normal white line tissue is apparent at the perimeter of the entire lesion. It is important that the edges of the debrided region blend smoothly with healthy wall (ie, no undermined wall is left in place). Tools and instruments used to debride white line lesions should be disinfected after the procedure. In severe cases, a large area of the wall may be compromised, and therapeutic shoeing may be necessary to support the remaining healthy tissue. However, the shoeing materials should not cover the debrided region because the exposed area must remain dry and well aerated. There are several commercially available soaks that are helpful after debridement. In mild cases, these products can be used when shoes are reset or feet are trimmed.
KERATOMA Although it is neither an infection nor infectious, keratomas (benign epidermal tumors within the hoof capsule) may be a source of recurrent hoof infection. Initially, keratomas usually present as abscess tracts that can be resolved with conservative treatment, but which later then recur. Radiographs characteristically show a distinct, scalloped area of osteolysis on the distal margin of P3. The borders of the lesion are smooth, which distinguishes keratoma from osteomyelitis of P3, in which the borders of the osteolytic area are rough. Treatment consists of hoof wall resection and tumor excision. Therapeutic shoeing is often required after surgery to support the surrounding hoof capsule and protect the surgical site. Exposed sensitive laminae epithelializes and, when complete excision of the keratoma is performed, the hoof wall grows out normally; therefore, complete recovery can be expected.
FINAL THOUGHTS Foot infections in the equine population are common. When severe or left untreated, these infections can end horse-related careers and can even be life-threatening in some cases. Therefore, they should be treated promptly and aggressively.