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Digital Infections in Cattle: Their Radiologic Spectrum
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SPECIAL ARTICLES
DIGITAL INFECTIONS IN CATTLE Their Radiologic Spectrum Charles S. Farrow, DVM
Infections of the digital region are the most common cause of lameness in cattle. Associated financial losses are considerable and usually result from a reduction in the animals' weight gain and milk production. Many such infections become economically unfeasible to treat, which results in the premature slaughter of the animals. Although superficial lesions may be adequately treated without the aid of radiography, the detection of deeper disorders requires radiographic assessment. CLINICAL ASPECTS
Affected cattle are usually between 1 and 10 years of age and have no relevant past medical history. Lameness is gradual in onset but tends to worsen rapidly with time. Almost invariably, home remedies have been tried that usually consist of soaks, poultices, wraps, and antibiotics. More often than not these remedies provide only temporary relief. Physical inspection of the infected part usually reveals one or more of the following abnormalities: varying degrees of altered weight-bearing, localized swelling, heat and hair loss proximal to the coronet, and granulation tissue and drainage in the proximal part of the interdigital space. Granulation tissue may also be seen protruding from vertically This article appeared in Veterinary Clinics of North America: Food Animal Practice, Vol. 1, No.1, March 1985, as part of an issue on Bovine Lameness and Orthopedics.
From the Department of Veterinary Anesthesiology, Radiology, and Surgery, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
VETERINARY CLINICS OF NORTH AMERICA: FOOD ANIMAL PRACTICE VOLUME 15 • NUMBER 2 • JULY 1999
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oriented cracks in the hoof wall. The hooves may be overgrown and spread laterally if there is much swelling of the interdigital space (Fig. 1). Relevant Anatomy
The bovine digital region is defined as those structures distal to the fetlock (metacarpo- and metatarsophalangeal joints). Internally, approximately half of these tissues are contained within the paired hooves. The latter are nearly symmetric but may appear differently depending on the perspective of the viewer. The paired digits are also nearly symmetric but are even more prone to appearing different because of their natural curvature, highly irregular contours, variable thickness, many vascular channels, and associated foramina. The relationship between the medial aspect of the hoof wall and the corresponding aspect of the distal interphalangeal joint space deserves special mention. This anatomic juxtaposition has been related previously to the high incidence of infection involving this joint. 1 Infections initiated in the interdigital space may extend laterally to the relatively unprotected distal interphalangeal joint with comparative ease (Fig. 2).
Figure 1. Infected bovine digits showing (a) hair loss, (b) drainage, (c) granulation tissue, and (d) a crack in the hoof wall.
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Figure 2. Bovine digit showing relationship of distal interphalangeal joint space to hoof wall. Notice relatively unprotected position of a joint medially (arrows).
Although they are not distinguishable individually on a radiograph, many vital nonosseous structures lie beneath the skin surface. Collectively, these tissues compose soft-tissue shadows surrounding the bones and joints (Fig. 3).
RADIOGRAPHY
The quality of bovine digital radiographs depends on a combination of technical skill and patient cooperation. Because the latter is highly variable and usually unpredictable, it is imperative to immobilize the affected part, either with ropes and the aid of assistants or, ideally, with a bovine restraint table (Fig. 4). Four standard views of the affected part should be made. Supplementary views should be made as required. The four standard views are the lateromedial, dorsopalmar or dorsoplantar, and two oblique (dorsomedial and dorsolateral) views. If further visualization of the distal phalanges is desired, one or two interdigital views may be made (Fig. 5). Low-output x-ray generators are capable of performing these examinations, although intermediate-powered machines will allow substan-
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Figure 3. Digital region showing underlying soft-tissue structures.
Figure 4. Secured cow on bovine restraint table in preparation for radiography.
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415
Figure 5. Stylized illustration showing relative positions of x-ray beam (arrows), foot (paired semicircles), and cassettes (bar) used to obtain four standard radiographic projections. These include (1) lateral view, (2) dorsopalmar/dorsoplantar view, and (3) dorsopalmarl dorsoplantar lateromedial and mediolateral oblique views. An optional interdigital position is shown (4).
tially reduced exposure times, which will decrease the likelihood of motion and the consequent indistinctness of structures. Rare earth intensifying screens and compatible film will further reduce the probability of motion problems. Settings of 2 MAS and 60 KVP are recommended in making the standard views, and settings of 3 MAS and 80 KVP are recommended when using nonscreen film for the interdigital radiographs. Focal-film distances that are commonly used are 30 cm.
RADIOLOGY Soft Tissues
Radiographic indicators of soft-tissue infection of the bovine foot include swelling, gas, mineralization, foreign bodies, and tissue defects. An increase in soft-tissue area and/ or density is a reliable indication of swelling, although it does not discriminate as to cause. Swelling may
416
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be localized to one aspect of the foot, such as the cranial surface; it may be confined to the interdigital space, which results in digital spreading (Fig. 6); or it may involve the entire foot. Gas within the soft tissues may be associated with atmospheric contamination via an open wound or tissue defect (Fig. 7). It may result from microbial metabolism, or it may be iatrogenic following aspiration, nerve block, or biopsy. Mineralization is usually of a dystrophic nature and often develops along natural soft-tissue planes such as tendons and ligaments. It may also develop within or surrounding natural cavities such as joints or bursa (Fig. 8). Foreign bodies must be metallic in order to be identified radiographically. Nails and wire are most commonly encountered and have usually penetrated the plantar or palmar surface (Fig. 9). Tissue defects may occur anywhere but are most often seen distally. These may be the result of direct trauma or occur secondary to tissue devitalization (see Fig. 7).
Joint Space
Indications of joint-space involvement include widening, narrowing, subchondral lysis, fracture, subluxation, and luxation. Widening of the joint space is one of the earliest and most reliable indicators of joint lesions in cattle. It is most commonly seen in the distal
Figure 6. Dorsopalmar view of digits showing spreading secondary to interdigital soft tissue swelling.
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Figure 7. Interdigital view of bovine digit showing pyramidal defect (large arrow) in dorsal aspect of sale with associated rectangular gas pocket (small arrows) lying ventral to the solar surface of the distal phalanx.
Figure 8. Dorsopalmar mediolateral oblique view of digit showing dystrophic mineralization superimposed on the navicular bone (arrow).
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Figure 9. Dorsoplantar view of bovine digit showing wire embedded in soft tissue lateral to mediodistal phalanx.
interphalangeal joint (Fig. lOA). Initially, widening may be subtle, but it tends to increase with time (Fig. lOB). Comparison with the width of the adjacent digit is useful. When no radiographic abnormalities are found but suspicions are high, progressive radiographic examinations are helpful. Joint-space narrowing is encountered only occasionally. It is possible that narrowing is most often detectable when radiography is done earlier in the disease process. Subchondral lysis develops following extension of the infection into the surrounding bone (Fig. 11). It may be focal, regional, or diffuse. Subchondral lysis often involves both sides of the joint but rarely to the same extent. Pathologic fractures often develop in advanced cases, usually in the form of avulsion-type injuries at or near the joint margins (Fig. 12A). These periarticular fractures often lead to destabilization of the involved joint with subsequent subluxation (Fig. 12B) or luxation (Fig. 12C).
Bone Bone alterations associated with infections are characterized by bone production, bone destruction, and sequestration (bone production is the most common alteration). New bone development may be classified
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Figure 10. A, Dorsopalmar view showing mild widening of laterodistal interphalangeal joint (arrow). (B), Dorsopalmar view of bovine digital region showing marked widening of laterodistal interphalangeal joint (arrow).
Figure 11. Dorsoplantar view of bovine digital region showing subchondral lysis of mediodistal interphalangeal joint (arrow).
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Figure 12. A, Dorsopalmar mediolateral oblique view of bovine digit showing periarticular avulsion fracture secondary to infection (arrow). B, Dorsopalmar view of bovine digital regions showing subluxation secondary to infection of mediodistal interphalangeal joint (arrow). C, Dorsolumbar view of bovine digit showing luxation of lateral distal interphalangeal joint secondary to infection (arrow).
DIGITAL INFECTIONS IN CATTLE
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according to location, which can be localized, regional, or diffuse. New bone development may be further characterized on the basis of maturity, which in tum provides a rough estimate of duration. A typical maturation sequence progresses from immature, to developing, to mature, and then to hypermature. These categories may in tum be related to early, intermediate, advanced, and long-standing lesions (Fig. 13A,B,C). Bone destruction, like production, may be localized, regional, or diffuse. It usually involves the subchondral tissues (Fig. 14A) but may also develop elsewhere (Fig. 14B). Sequestra may be traumatic or infective and are most frequently seen in the distal phalanges. They may occur dorsally (Fig. 15A), distally (Fig. 15B), or along the plantar or palmar margins (Fig. 15C).
CONCLUSION
By using a systematic approach, the radiographic signs of bovine foot infections, including infections of the regional soft tissues, joint spaces, and bones, may be detected readily. This information is often of primary importance in deciding on a specific method of treatment. Furthermore, a radiographic assessment is the only practical method of
Figure 13. A, Dorsopalmar view of bovine digit showing immature (early) new bone formation on lateral aspect of medial middle phalanx (arrows). B, Dorsopalmar view of bovine digit showing mature (advanced) new bone formation on lateral aspect of lateral middle phalanx (arrow). C, Dorsopalmar view of bovine digital region showing hypermature (longstanding) new bone formation on all aspects of right forelimb distally.
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Figure 14. A, Dorsoplantar view of bovine digital region showing subchondral lysis in the distal aspect of medial middle phalanx (arrow). B, Dorsopalmar view of bovine digit showing destruction of distal aspect of lateral distal phalanx (arrow).
establishing the magnitude and extent of a given infectious process; this information is necessary for formulation of an accurate prognosis. In addition, radiographic documentation of infectious foot disease may be required by an insurance carrier prior to claim settlement. Because of the availability and moderate cost of radiologic technology, a radiographic examination should be made in all cases of suspected foot infections in cattle.
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Figure 15. A, Interdigital view of bovine digit showing sequestrum dorsally (arrow). B, Interdigital view of bovine digit showing sequestrum distally (arrow). C, Interdigital view of bovine digit showing sequestrum ventral to midpalmar margin (arrow).
Reference 1. Greenough PR, MacCallum FJ, Weaver AD: Lameness in Cattle. Philadelphia, J. B. Lippincott Co., 1972
Address reprint requests to Charles S. Farrow, DVM Department of Veterinary Anesthesiology, Radiology, and Surgery Western College of Veterinary Medicine University of Saskatchewan 52 Campus Drive Saskatoon, SK S7N 5B4 Canada e-mail: [email protected]
SPECIAL ARTICLES
DIGITAL INFECTIONS IN CATTLE Their Radiologic Spectrum Charles S. Farrow, DVM
Infections of the digital region are the most common cause of lameness in cattle. Associated financial losses are considerable and usually result from a reduction in the animals' weight gain and milk production. Many such infections become economically unfeasible to treat, which results in the premature slaughter of the animals. Although superficial lesions may be adequately treated without the aid of radiography, the detection of deeper disorders requires radiographic assessment. CLINICAL ASPECTS
Affected cattle are usually between 1 and 10 years of age and have no relevant past medical history. Lameness is gradual in onset but tends to worsen rapidly with time. Almost invariably, home remedies have been tried that usually consist of soaks, poultices, wraps, and antibiotics. More often than not these remedies provide only temporary relief. Physical inspection of the infected part usually reveals one or more of the following abnormalities: varying degrees of altered weight-bearing, localized swelling, heat and hair loss proximal to the coronet, and granulation tissue and drainage in the proximal part of the interdigital space. Granulation tissue may also be seen protruding from vertically This article appeared in Veterinary Clinics of North America: Food Animal Practice, Vol. 1, No.1, March 1985, as part of an issue on Bovine Lameness and Orthopedics.
From the Department of Veterinary Anesthesiology, Radiology, and Surgery, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada
VETERINARY CLINICS OF NORTH AMERICA: FOOD ANIMAL PRACTICE VOLUME 15 • NUMBER 2 • JULY 1999
411
412
FARROW
oriented cracks in the hoof wall. The hooves may be overgrown and spread laterally if there is much swelling of the interdigital space (Fig. 1). Relevant Anatomy
The bovine digital region is defined as those structures distal to the fetlock (metacarpo- and metatarsophalangeal joints). Internally, approximately half of these tissues are contained within the paired hooves. The latter are nearly symmetric but may appear differently depending on the perspective of the viewer. The paired digits are also nearly symmetric but are even more prone to appearing different because of their natural curvature, highly irregular contours, variable thickness, many vascular channels, and associated foramina. The relationship between the medial aspect of the hoof wall and the corresponding aspect of the distal interphalangeal joint space deserves special mention. This anatomic juxtaposition has been related previously to the high incidence of infection involving this joint. 1 Infections initiated in the interdigital space may extend laterally to the relatively unprotected distal interphalangeal joint with comparative ease (Fig. 2).
Figure 1. Infected bovine digits showing (a) hair loss, (b) drainage, (c) granulation tissue, and (d) a crack in the hoof wall.
DIGITAL INFECTIONS IN CATTLE
413
Figure 2. Bovine digit showing relationship of distal interphalangeal joint space to hoof wall. Notice relatively unprotected position of a joint medially (arrows).
Although they are not distinguishable individually on a radiograph, many vital nonosseous structures lie beneath the skin surface. Collectively, these tissues compose soft-tissue shadows surrounding the bones and joints (Fig. 3).
RADIOGRAPHY
The quality of bovine digital radiographs depends on a combination of technical skill and patient cooperation. Because the latter is highly variable and usually unpredictable, it is imperative to immobilize the affected part, either with ropes and the aid of assistants or, ideally, with a bovine restraint table (Fig. 4). Four standard views of the affected part should be made. Supplementary views should be made as required. The four standard views are the lateromedial, dorsopalmar or dorsoplantar, and two oblique (dorsomedial and dorsolateral) views. If further visualization of the distal phalanges is desired, one or two interdigital views may be made (Fig. 5). Low-output x-ray generators are capable of performing these examinations, although intermediate-powered machines will allow substan-
414
FARROW
Figure 3. Digital region showing underlying soft-tissue structures.
Figure 4. Secured cow on bovine restraint table in preparation for radiography.
DIGITAL INFECTIONS IN CATTLE
415
Figure 5. Stylized illustration showing relative positions of x-ray beam (arrows), foot (paired semicircles), and cassettes (bar) used to obtain four standard radiographic projections. These include (1) lateral view, (2) dorsopalmar/dorsoplantar view, and (3) dorsopalmarl dorsoplantar lateromedial and mediolateral oblique views. An optional interdigital position is shown (4).
tially reduced exposure times, which will decrease the likelihood of motion and the consequent indistinctness of structures. Rare earth intensifying screens and compatible film will further reduce the probability of motion problems. Settings of 2 MAS and 60 KVP are recommended in making the standard views, and settings of 3 MAS and 80 KVP are recommended when using nonscreen film for the interdigital radiographs. Focal-film distances that are commonly used are 30 cm.
RADIOLOGY Soft Tissues
Radiographic indicators of soft-tissue infection of the bovine foot include swelling, gas, mineralization, foreign bodies, and tissue defects. An increase in soft-tissue area and/ or density is a reliable indication of swelling, although it does not discriminate as to cause. Swelling may
416
FARROW
be localized to one aspect of the foot, such as the cranial surface; it may be confined to the interdigital space, which results in digital spreading (Fig. 6); or it may involve the entire foot. Gas within the soft tissues may be associated with atmospheric contamination via an open wound or tissue defect (Fig. 7). It may result from microbial metabolism, or it may be iatrogenic following aspiration, nerve block, or biopsy. Mineralization is usually of a dystrophic nature and often develops along natural soft-tissue planes such as tendons and ligaments. It may also develop within or surrounding natural cavities such as joints or bursa (Fig. 8). Foreign bodies must be metallic in order to be identified radiographically. Nails and wire are most commonly encountered and have usually penetrated the plantar or palmar surface (Fig. 9). Tissue defects may occur anywhere but are most often seen distally. These may be the result of direct trauma or occur secondary to tissue devitalization (see Fig. 7).
Joint Space
Indications of joint-space involvement include widening, narrowing, subchondral lysis, fracture, subluxation, and luxation. Widening of the joint space is one of the earliest and most reliable indicators of joint lesions in cattle. It is most commonly seen in the distal
Figure 6. Dorsopalmar view of digits showing spreading secondary to interdigital soft tissue swelling.
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417
Figure 7. Interdigital view of bovine digit showing pyramidal defect (large arrow) in dorsal aspect of sale with associated rectangular gas pocket (small arrows) lying ventral to the solar surface of the distal phalanx.
Figure 8. Dorsopalmar mediolateral oblique view of digit showing dystrophic mineralization superimposed on the navicular bone (arrow).
418
FARROW
Figure 9. Dorsoplantar view of bovine digit showing wire embedded in soft tissue lateral to mediodistal phalanx.
interphalangeal joint (Fig. lOA). Initially, widening may be subtle, but it tends to increase with time (Fig. lOB). Comparison with the width of the adjacent digit is useful. When no radiographic abnormalities are found but suspicions are high, progressive radiographic examinations are helpful. Joint-space narrowing is encountered only occasionally. It is possible that narrowing is most often detectable when radiography is done earlier in the disease process. Subchondral lysis develops following extension of the infection into the surrounding bone (Fig. 11). It may be focal, regional, or diffuse. Subchondral lysis often involves both sides of the joint but rarely to the same extent. Pathologic fractures often develop in advanced cases, usually in the form of avulsion-type injuries at or near the joint margins (Fig. 12A). These periarticular fractures often lead to destabilization of the involved joint with subsequent subluxation (Fig. 12B) or luxation (Fig. 12C).
Bone Bone alterations associated with infections are characterized by bone production, bone destruction, and sequestration (bone production is the most common alteration). New bone development may be classified
DIGITAL INFECTIONS IN CATTLE
419
Figure 10. A, Dorsopalmar view showing mild widening of laterodistal interphalangeal joint (arrow). (B), Dorsopalmar view of bovine digital region showing marked widening of laterodistal interphalangeal joint (arrow).
Figure 11. Dorsoplantar view of bovine digital region showing subchondral lysis of mediodistal interphalangeal joint (arrow).
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FARROW
Figure 12. A, Dorsopalmar mediolateral oblique view of bovine digit showing periarticular avulsion fracture secondary to infection (arrow). B, Dorsopalmar view of bovine digital regions showing subluxation secondary to infection of mediodistal interphalangeal joint (arrow). C, Dorsolumbar view of bovine digit showing luxation of lateral distal interphalangeal joint secondary to infection (arrow).
DIGITAL INFECTIONS IN CATTLE
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according to location, which can be localized, regional, or diffuse. New bone development may be further characterized on the basis of maturity, which in tum provides a rough estimate of duration. A typical maturation sequence progresses from immature, to developing, to mature, and then to hypermature. These categories may in tum be related to early, intermediate, advanced, and long-standing lesions (Fig. 13A,B,C). Bone destruction, like production, may be localized, regional, or diffuse. It usually involves the subchondral tissues (Fig. 14A) but may also develop elsewhere (Fig. 14B). Sequestra may be traumatic or infective and are most frequently seen in the distal phalanges. They may occur dorsally (Fig. 15A), distally (Fig. 15B), or along the plantar or palmar margins (Fig. 15C).
CONCLUSION
By using a systematic approach, the radiographic signs of bovine foot infections, including infections of the regional soft tissues, joint spaces, and bones, may be detected readily. This information is often of primary importance in deciding on a specific method of treatment. Furthermore, a radiographic assessment is the only practical method of
Figure 13. A, Dorsopalmar view of bovine digit showing immature (early) new bone formation on lateral aspect of medial middle phalanx (arrows). B, Dorsopalmar view of bovine digit showing mature (advanced) new bone formation on lateral aspect of lateral middle phalanx (arrow). C, Dorsopalmar view of bovine digital region showing hypermature (longstanding) new bone formation on all aspects of right forelimb distally.
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FARROW
Figure 14. A, Dorsoplantar view of bovine digital region showing subchondral lysis in the distal aspect of medial middle phalanx (arrow). B, Dorsopalmar view of bovine digit showing destruction of distal aspect of lateral distal phalanx (arrow).
establishing the magnitude and extent of a given infectious process; this information is necessary for formulation of an accurate prognosis. In addition, radiographic documentation of infectious foot disease may be required by an insurance carrier prior to claim settlement. Because of the availability and moderate cost of radiologic technology, a radiographic examination should be made in all cases of suspected foot infections in cattle.
DIGITAL INFECTIONS IN CATTLE
423
Figure 15. A, Interdigital view of bovine digit showing sequestrum dorsally (arrow). B, Interdigital view of bovine digit showing sequestrum distally (arrow). C, Interdigital view of bovine digit showing sequestrum ventral to midpalmar margin (arrow).
Reference 1. Greenough PR, MacCallum FJ, Weaver AD: Lameness in Cattle. Philadelphia, J. B. Lippincott Co., 1972
Address reprint requests to Charles S. Farrow, DVM Department of Veterinary Anesthesiology, Radiology, and Surgery Western College of Veterinary Medicine University of Saskatchewan 52 Campus Drive Saskatoon, SK S7N 5B4 Canada e-mail: [email protected]