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Lameness in Foals
C H A P T E R
Lameness in Foals
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SCOTT E. MORRISON
T
he newborn foal can be affected by many congenital and acquired conditions that influence normal limb function and ambulation. Of all congenital deformities in the foal, congenital musculoskeletal abnormalities are the most common, with flexural and angular deformities being the most frequent congenital causes of lameness. However, not all congenital musculoskeletal deformities will cause lameness in the foal, and some may not become clinically evident until the foal matures and begins training. Acquired conditions in the newborn foal are a response to an event that occurs shortly after birth.
CONTRACTURES
Contractures are congenital conditions that typically affect bigger foals, but they can be seen in all body types. They range from upright fetlocks and pasterns to being over at the knee to severe deformities resulting in loss of use of the limb. One or more limbs can be affected, and the contracture can involve the deep digital or superficial flexor tendon, the suspensory ligament, the joint capsules, or any combination thereof. In foals with deep digital flexor tendon contracture, also known as ballerina syndrome, the heel does not contact the ground, and the foal walks on the toe or dorsal hoof wall. In severe bilateral cases, the foal is unable to stand. With superficial flexor tendon contracture, in contrast, the foot can be placed flat on the ground, but the fetlock and pastern buckle forward (Figure 183-1).
Etiology The cause of tendon contracture is unknown. Spatial restriction on the growth of large foals in utero is a theory commonly proposed to explain development of contractures, and in support of this was the finding in one study that the placentas of eight Thoroughbred foals with limb contractures were smaller than those of normal foals. There seems to be no correlation between the incidence of contractures and mare age, and the condition does not seem to be inherited. Because flexural deformities seem to be more common in some years than others and appear to come in groups, toxins (locoweed, Sudan grass, iodide toxicosis, or goiter) and influenza infection have been implicated, possibly by causing neuromuscular disorders in the developing limb. Bilateral limb contractures may be part of a larger complex known as contracted foal syndrome, which encompasses multiple developmental disorders, including bilateral limb contracture, torticollis, scoliosis, asymmetry of the skull, and attenuation or thinning of the ventral abdominal wall with possible eventration.
Treatment Treatment of appendicular contractures consists of medical treatment with oxytetracycline (3 g diluted in 150 mL saline solution and given intravenously over 10 minutes, once daily
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for 3 days) combined with mechanical stretching of the contracture with splints, braces, or both. Some degree of pain and discomfort can be expected from the splinting process, and administration of antiinflammatory drugs and antiulcer medication should be considered. Contractures become progressively harder to treat successfully with age. For this reason, treating affected foals early and aggressively is imperative; ideally, these foals are evaluated and treated on the first day of life. The typical newborn foal is sedated with intravenously administered butorphanol (3 mg) combined with xylazine (30 mg) and placed in lateral recumbency in the stall with the eyes covered by a towel. The limb is bandaged with a cotton combine bandage or quilt to the full extent of the contracture. For distal interphalangeal and fetlock contractures, the bandage is applied from the hoof to the proximal part of the cannon bone. For carpal contractures, the limb is bandaged from the cannon bone to the elbow. If the contractures extend from the distal interphalangeal joint through the fetlock and carpus, the bandage must also extend from hoof to elbow. The cotton combine bandage must be firmly secured with Vetrap1 or a similar product. The limb is held in extension, and a 3- or 4-inch-wide roll of fiberglass casting material is unrolled, folded to the length of the bandage, and applied to the palmar or plantar aspect of the limb. While the contracted joints are held in extension by direct manual pressure on the dorsum of the involved joints, the cast splint is bandaged to the limb with adhesive bandaging tape. Care should be taken not to bandage the splint to the limb too tightly or create a wrinkle in the splint material to avoid creating pressure points and skin sores. The pressure and forced extension are held until the cast has set. If the distal interphalangeal joint is involved, the cast splint must be extended to under the solar surface of the foot and at least one third of the way up the dorsal wall of the hoof (Figure 183-2). When the carpus is contracted, care should be taken not to bandage the splint too tightly in the antebrachial region because this can cause radial nerve paralysis. The splint is usually changed daily, making a new splint and achieving more correction each time. Most cases can be corrected within 3 to 4 days. Foals in which more than one limb is involved may need assistance to stand and nurse. After the limb contracture is corrected with splinting, the leg is maintained in a bandage for a few days to gradually decrease the level of support, and the foal is slowly introduced to turnout and exercise. In the author’s experience, a proportion of these foals will appear normal for a couple of months and then slowly develop an acquired club foot in one of the limbs. For this reason, cases of contracture should be closely monitored throughout their growth and
1
Vetrap, 3M.
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183 Lameness in Foals
C
Figure 183-1 Foals with tendon contractures. Contracture of the deep digital flexor tendon in the left hind limb (A); contracture of the superficial flexor tendon before (B) and after (C) splinting for 3 days.
A
B Figure 183-2 A, Splinting technique for deep digital flexor tendon contracture of the right forelimb. The foal is lying in left lateral recumbency (hoof is to the left). The bandages are applied around the limb, and the casting tape is being applied along the long axis of the limb. B, In this foal, the right hind limb is in a splint cast that is protected with a bandage.
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XVI The Foal safer to address these cases with bandages and splints, because these methods distribute the stress over a larger area. When toe extensions are used in mild cases, the foal should be monitored daily for lameness, which may indicate lamellar tearing. In those instances, the extension must be removed. In lame foals that have pain in the toe region, radiographs should be taken to rule out mechanical laminitis.
FLEXOR TENDON LAXITY
Figure 183-3 A toe extension (toe reinforcement) applied to a congenital club foot. The toe extension is made with an acrylic and fiberglass fabric compound.
Figure 183-4 Close-up of view of a shear lesion at the anterior coronary band of the hind foot of a foal that had a heel extension shoe placed too early in life.
development. Many of these foals eventually become sound athletes. Slight deep digital flexor tendon contracture may respond to stall rest, bandaging, and administration of antiinflammatory drugs. If the toe length is short or is being worn excessively, a toe extension may provide more leverage to lower the heel and stretch the contracted tendon (Figure 183-3). These toe extensions should, however, be used with caution because when they are applied, only a small area of the hoof is being used to counter and correct the contracture. Excessive strain concentrated on the immature toe region can cause tearing of the pedal bone away from the hoof wall, laminitis, or both. Because some cases can develop separation of the anterior part of the coronary band or shear lesion (Figure 183-4), shoes or toe extensions should not be applied within the first week of life, when the soft immature hoof and lamellar interface are more prone to failure. It is much
Laxity of the flexor tendons is another congenital condition that typically is seen in dysmature or premature foals, but the condition also occurs in otherwise normal foals. Flexor tendon laxity can affect one or more limbs but usually occurs in the hind limbs (Figure 183-5). The laxity and associated hyperextension commonly involve the phalangeal and metacarpal or metatarsal joints. Some cases also have hyperextension of the carpus or hyperflexion of the tarsus; such animals are said to be “back at the knee” or “sickle hocked,” respectively. Most of these foals improve within the first week of life. Many are also born with excessive hoof growth, so trimming the feet removes toe length, moves the heel position caudally, helps decrease the hyperextension of the distal interphalangeal joint, and helps prevent the toe from turning upward (Figure 183-6). Foals with flexor tendon laxity should be managed with stall rest and controlled exercise, such as hand walking the mare in the barn aisle several times daily while the foal follows. After the muscles and tendons strengthen, the mare and foal can begin turnout into a small paddock. Foals that are back at the knee or sickle hocked should not be allowed to exercise before radiographs have been taken to ensure that the carpal and tarsal bones are fully ossified; crushing of the incompletely ossified carpal or tarsal bones can create permanent wedge-shaped cuboidal bones and lameness. In foals that do not improve within a week or that develop heel bulb ulcerations, heel extensions can help provide caudal leverage and force the toe onto the ground. Heel extensions are usually cuffed shoes, which are attached to the hoof wall with epoxy or acrylic adhesive. These shoes are typically left on for 10 to 14 days, after which the hoof is trimmed and the foal is reevaluated. It is important not to attach the cuff to the heel region of the foot because the area is under stress and easily pinched or bruised by the glue. For this reason, the cuffed shoe should be modified by cutting the cuff away from the back half of the hoof and leaving cuff only to be attached to the toe of the hoof. After the cuff has been on for 5 days, the heel extension can be shortened by 50% with hoof nippers. After another 5 to 9 days, the shoe will need to be removed and the hoof trimmed. Most foals will have strengthened by this time and can be left barefoot. Some may require a second shoe application. If possible, the limbs of foals with tendon laxity should not be bandaged because the additional support causes further relaxation of the tendons and ligaments, worsening the laxity. If a bandage is required to protect an ulcerated area or sore on the fetlock or heel bulb, it should be loosely applied to just that area and not extended up the limb. The occasional foal with severe laxity is unresponsive to treatment (Figure 183-7).
ANGULAR DEFORMITIES
Angular deformities can be congenital or acquired and are common in the newborn foal. They are classified as valgus or varus according to whether the limb deviation is lateral or medial to the axis of limb, respectively. Foals with mild deformities are often sound, but those with more severe angular deformities can be lame because the limb instability
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over the medial or lateral region of the growth plate, which is sometimes referred to as physitis. Angular deformities can be classified as articular, diaphyseal, or physeal in origin. If the deformity can be straightened manually, it is the result of an articular deformity, which can be the consequence of incomplete ossification (usually the carpus or hock), uterine malpositioning, or flaccidity of the periarticular structures. Articular deformities respond well to rest, time, and application of some external form of support such as bandaging and splinting, if the angulation is severe. If incomplete ossification goes unnoticed, it can result in permanent deformity by the time the foal is several weeks old. Diaphyseal angular deformities are less common and originate along the diaphysis of the bone, giving the bone a bowed appearance. Physeal angular deformities are the result of congenital or acquired asymmetric growth of the metaphysis or epiphysis.
A
B
C Figure 183-5 Hind feet of a foal with flexor tendon laxity. A, The foal is resting on the bulbs of the heels, which results in development of heel bulb ulcers (B). C, A heel extension shoe has been glued to the foot. Notice how the cuff is trimmed away from the heel region so that it is only adherent to the toe region.
and abnormal loading of joints causes joint instability, physitis, and abnormal or excessive hoof wear. The normal newborn foal should have a moderate degree of carpal, tarsal, and fetlock joint valgus conformation and slight outward rotation of all four limbs (Figure 183-8). As long as the loading forces on the physis are within the normal physiologic range of the physeal cartilage, most valgus deformities improve with time. This is because physeal cartilage growth increases in response to compressive forces. However, if angular deformities are more severe and compressive forces are excessive, physeal growth slows. Foals with excessive compressive forces usually develop signs of pain and swelling
Treatment Treatment of angular deformities depends on severity, location, and how the joint angles change over time. The two main areas of interest with regard to managing the foot are the physis of the distal metacarpus or metatarsus and the physis of the distal radius. The management and treatment goals are to prevent and correct the excessive angular deformities or those that will create excessive compression on the growth plate and retard normal corrective physeal growth. Any varus deformity, and an excessive degree of valgus deformity, is abnormal. Constant improvement or self-correction is the desired trend in response to treatment. Frequent monitoring of the foal is paramount for early detection of limbs that are not improving with time so that proper intervention can be implemented to help correct the deformity. An understanding of the tools available and limitations of each is necessary to effectively implement a foal foot management plan. Equally as important as foot care is recognizing which limb abnormalities will respond favorably to foot manipulations and which may necessitate other treatment modalities, such as transphyseal bridge surgery. Distal metacarpal or metatarsal angular deformities (fetlock varus or fetlock valgus) are common. Because foot manipulations have most influence on the distal part of the limb and less influence proximally, fetlock angular deformities are most likely to respond to foot trimming or shoeing. Distal physes in the metacarpal and metatarsal bones close by 4 to 5 months and lose 50% of their growth potential every 30 days up to that time. Consequently, it is imperative that fetlock angular limb deformity be appropriately managed at an early age. The goal is to maintain the center of the foot directly perpendicular to the upright cannon bone (imagine a plumb line dropped through the center of the cannon bone to the center of the foot) while ignoring the angulation of the carpus or tarsus. One of the most common mistakes made in treatment of angular deformities is trying to correct a carpal angular deformity by use of foot manipulations at an early age and in the process worsening or creating a fetlock angular deformity. For this reason, emphasis should be on establishing fetlock alignment during the first 3 to 4 months and then, after the distal metacarpal or metatarsal physis has closed, shifting the focus to the carpus because the distal radial physis does not close physiologically until 14 months of age. Valgus deformities of the fetlock usually improve with time and typically do not require treatment unless severe. Fetlock varus, on the other hand, generally does not improve with time and requires trimming, application of shoe extensions, or surgical correction.
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A
C
B
D
Figure 183-6 A, A newborn foal foot with mild flexor tendon laxity, which results in the weight being borne on the heels. Trimming away the excessive hoof tissue to move the heel position caudally (B and C) resulted in a more normal posture (D).
Trimming alone can be effective in treating mild angular deformities of the fetlock region. If, however, the selfcorrecting mechanism is failing to improve the angular deformity, then one must assume that the medial region of the physis in a varus deformity or the lateral aspect of the physis in a valgus deformity is overloaded and growth is decreased in that region of the physis. Trimming and shoeing techniques to help decrease compressive forces on the medial or lateral region of the physis can alter physeal growth and encourage straightening of the limb. For example, lowering the medial side of the foot will decrease compression on the medial aspect of the bone column and increase compression laterally. Decreasing the height of the hoof wall on one side of the limb increases compressive force on the contralateral, longer side and creates tension on the “short” side of the foot, bone column, and physis. Additionally, lowering one side of the foot changes the manner in which the foot strikes the ground and becomes loaded: the longer side of the hoof strikes the ground first, causing the limb to align closer to the long side of the hoof. This potentially encourages loading on the longer side. If the trim alone aligns the foot with the
center of the cannon bone, trimming every 2 to 3 weeks may be sufficient to correct the angular deformity. Care should be taken when trimming foals’ feet. Overtrimming will cause bruising, wing fractures, and lameness. The foot should be routinely examined by digital palpation, and during the trim, as much sole as possible should be left in place for protection. Rolling the edge of the hoof wall can provide some degree of correction without invading sole mass. If the desired foot position cannot be achieved with the trim alone, application of a hoof extension is required. Shoes are recommended in foals that require more than 1 cm of correction and in those that become footsore from corrective trimming. Shoes provide correction while protecting the sole and do not cause focal tearing in one region of the hoof wall (Figure 183-9). If a fetlock deformity does not improve by 60 days and is severe, surgical placement of a transphyseal bridge may be indicated. Carpal deformities should be graded on that basis of severity. Slight (2 to 5 degrees) carpal valgus is normal in newborn foals of good conformation, and most cases of carpal valgus improve within 30 days. Surgical intervention may be
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indicated if the deformity stops improving or changes for the worse. Careful monitoring and scoring of the deformity is therefore important. In foals with severe carpal deformity, carpal radiographs should be taken to evaluate the cuboidal bones. Delayed ossification of the cuboidal bones makes enforced stall rest necessary until the bones have matured. If, however, there
183 Lameness in Foals
is angular deformity but the cuboidal bones are mature, the foal can be turned out for short periods. Shoes with medial extensions can be helpful in managing carpal valgus deformities, but care should be taken to not create a fetlock varus deformity in the process. This is especially important during the first 4 to 5 months of age (Figure 183-10). When a shoe is applied for a carpal angular deformity, the foot should be trimmed and balanced so that it is centered more perpendicular to the long axis of the cannon bone, with an extension used to support the carpal deformity. Unlike with fetlock angular deformities, altering hoof length medial to lateral is unlikely to have a significant beneficial effect on the physis of the upper limb and will only unnecessarily distort the hoof. Windswept foals have a conformational abnormality in which one limb has a varus deformity and the opposite limb has a valgus deformity. This condition can occur in the forelimbs or hind limbs. The condition will self-correct with time and does not warrant surgical intervention. The foot should be trimmed and balanced. If the hoof is rolling over on the medial aspect of the valgus limb or the lateral aspect of the varus limb, a shoe with a medial extension (for the valgus limb) or a lateral extension (for the varus limb) can be applied to help direct and support the foot directly beneath the bone column.
ROTATIONAL DEFORMITIES
Figure 183-7 A foal with severe hind limb flexor tendon laxity that failed to improve after 30 days of controlled exercise and use of heel extensions.
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B
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Newborn foals normally have slight outward rotation of the limbs, but this improves as the muscles of the chest and hindquarters develop. Rotational deformities that originate high in the limb are likely to improve with time. Rotational deformities that originate distal to the carpus generally do not improve. The author does not recommend correction of a rotational deformity by trimming and shoeing. The foot should be trimmed such that it is maintained directly beneath the cannon bone when viewed directly in front of the dorsal surface of that limb. Trying to correct a rotational deformity by trimming or shoeing the foot usually adds a fetlock
C
Figure 183-8 A foal with carpal valgus that improved over 6 weeks without treatment. Images show foal at 1 (A), 6 (B), and 9 (C) weeks of age.
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XVI The Foal metacarpus and the distal metacarpal physis, often creating a fetlock varus deformity. The offset knee cannot be corrected, but efforts should be taken to prevent a fetlock varus deformity from developing.
TRAUMATIC INJURIES OF THE FOOT Examination of the Foot
Figure 183-9 Foot extension of the type used when desired foot position cannot be achieved by trimming alone or when the foal requires more than 1 cm of correction. Notice the physitis of the distal metacarpus and the proximal phalanx.
In foals, common causes of acute-onset lameness are sole bruising, pedal bone fractures, and local infections. Diagnosis begins with examination of the foal at a walk and trot, if necessary. It is helpful to watch the foal walk or trot freely while the mare is led. When young foals are led, they often lean into or away from the holder, making gait evaluation difficult. After the lame limb is identified, thorough evaluation of the foot is performed. The foot should be cleaned and brushed out. The coronary band, heel bulbs, and pastern should be palpated for pain or swelling. The lame foot will have an exaggerated digital pulse. Examination with hoof testers will help locate the area of soreness. Because most foals will give false-positive responses to application of hoof testers, mild sedation will help improve the accuracy of the hoof-tester examination. A repeatable response to gentle hoof-tester pressure is considered a positive response. The coffin and pastern joints are flexed and palpated for pain, heat, or effusion. Diagnostic nerve blocks can help confirm the foot as the source of lameness. When the area of soreness is located, the foot is trimmed and closely inspected for defects in the sole or white line.
Bruising of the Foot Bruising of the foot is typically diagnosed by ruling out other causes of foot lameness. Bruises typically improve with time. Bandaging or applying a poultice to the foot, stall rest, and use of nonsteroidal antiinflammatory medications can speed recovery. Severe bone contusions, which can be confirmed by magnetic resonance imaging, can take longer to resolve.
Local Infections
Figure 183-10 Right front carpal valgus with fetlock varus conformation. The fetlock varus was caused by trying to correct the carpal valgus through trimming and shoeing.
angular deformity to the preexisting rotational deformity. Some practitioners advocate the use of a medial toe extension to force the foot to breakover at its center and to prevent it from breaking over on the medial quarter. This treatment does not correct the rotational deformity, but rather, the hoof capsule will develop a twisted or distorted appearance, or wry foot. The offset or “bench” knee conformation is an axial deformity in which the carpus is offset laterally to the metacarpus. This places more stress on the medial aspect of both the
If the lameness worsens with time, an infection should be considered. Most abscesses are detected through close inspection of the sore area of the foot. Defects in the sole, frog, or white line should be carefully debrided and trimmed out or followed down to the site of infection. The abscess should be adequately opened to allow drainage and prevent premature closure of the hole. A small double-edged abscess knife or a bone curette is useful for the latter procedure. If the infection cannot be located, an overnight poultice can be applied to the foot to encourage the abscess to mature. The poultice can be a wet Animalintex2 pad or other poultice product bandaged to the foot. The foal should be noticeably improved within the 2 days following abscess drainage. If the lameness persists without improvement or if drainage continues for more than 3 days, radiographs should be taken to evaluate the health of the pedal bone. Septic osteitis of the pedal bone is typically evident on radiographs within 3 to 5 days of onset of infection at the site. Septic osteitis of the pedal bone is seen as a focal irregular demineralization of the solar margin with gas or fluid opacities (Figure 183-11). Larger areas of infection may have larger areas of demineralization or sequestrum formation. Some cases may take longer to become evident radiographically, so if lameness persists, radiographs should be repeated as needed. Pedal bone septic osteitis warrants culture and
2
Animalintex Poultice Pad, 3M.
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183 Lameness in Foals
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B
Figure 183-11 Radiographs of two cases of septic pedal osteitis. A, Small focal area of osteomyelitis at the toe region of the pedal bone. B, Large area of osteomyelitis at the toe region of the pedal bone.
antimicrobial sensitivity testing. Treatment involves surgical debridement, administration of systemic antimicrobials, and possibly regional limb perfusion (see Chapter 186). Focal areas of septic osteitis can be effectively treated with medicalgrade larval therapy (also referred to as maggot therapy) and systemic antimicrobials.
Puncture Wounds Puncture wounds of the foot can be difficult to detect and inspect because tracts close quickly in the very elastic and pliable foal hoof. If a puncture to the sole or frog is suspected, the sore area should be pared down and gently inspected with a blunt-tipped, malleable probe. This part of the examination is usually performed with the foal under sedation and the foot desensitized with an abaxial sesamoid nerve block. When the tract is identified, the foot should be scrubbed and prepared for deeper inspection and a fistulogram. Deeper inspection includes probing the tract to determine the depth and direction of the wound. The fistulogram identifies the extent of the infection and involvement of synovial structures (Figure 183-12). It is performed by injecting 5 mL of radiopaque contrast material through a tomcat or 18-gauge, 3-inch catheter that has been inserted into the tract as far as it will go. The contrast material will leak out of the tract and onto the external surface of the sole and hoof and should be wiped off with alcohol-soaked gauze before the foot is placed on a radiograph block. Lateral and horizontal anterior-posterior views are taken. Suspected synovial infection detected on the fistulogram can be confirmed by arthrocentesis. Sepsis of a synovial structure (phalangeal joint, tendon sheath, or navicular bursa) requires aggressive daily lavage of the involved structures, regional limb antimicrobial
perfusions, and systemic broad-spectrum antimicrobials. Synovial fluid samples should be submitted for determination of the leukocyte count and total protein concentration and for bacterial culture. The foal’s comfort level, the leukocyte count of the synovial fluid retrieved before each lavage, and serum analyte concentration are the most common methods used to monitor progression of the infection. Daily lavage is recommended until the cell counts are normal and the foal is walking well. If lameness worsens after cessation of the lavage, centesis and white blood cell count should be repeated.
Injuries to the Hoof Capsule Injuries to the hoof wall, such as wall avulsions and fractures of the wall, sole, or pedal bone, are common and can result from kicking a fence or wall, stepping on a rock, or being stepped on by the mare. All traumatic injuries of the foot should be examined and radiographed to assess for involvement of deeper structures. With the foal sedated and the foot desensitized, the area of wall damage should be soaked, scrubbed, and disinfected. If the lesion is bleeding profusely, it may be helpful to apply a tourniquet. If the avulsion involves only the hoof capsule and the underlying corium is not damaged, the detached wall can be debrided and cut away. The exposed corium should be dressed with povidone-iodine solution or povidone cream and a heavily padded bandage. If the wall detachment involves more than one third of the hoof wall, a foot cast may be needed to stabilize the compromised hoof and improve comfort. The first foot cast should be changed in 3 to 4 days, then every 2 weeks thereafter until the hoof becomes cornified (Figure 183-13). If the avulsion involves deep lacerations to the coronet or pastern, surgical repair and
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Figure 183-12 Three examples of fistulograms from horses with puncture wounds of the hoof. A, Frog puncture wound with involvement and communication with tendon sheath. B, Anterior coronary band puncture wound with distal interphalangeal joint involvement. C, Wire puncture wound showing no synovial structure involvement.
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B
C
Figure 183-13 Hoof avulsion in a foal. The foot is shown immediately after wall avulsion (A), after 2 weeks of foot casting (B), and after 4 months (C).
sutures are required for the best result and to prevent abnormal coronary band wall growth. Sole fractures are the result of kicking or stepping on a firm object. Acute lameness and a cracked sole are seen on examination. Serum discharge is often seen on the margins of the sole crack. The bed of the crack is often contaminated with debris. Opening the margins of the crack, debriding the bed of the crack, and soaking and cleansing the defect are recommended. Applying a shoe with a removable treatment plate helps suspend and protect the damaged sole. This improves the lameness immediately and speeds recovery. The shoe is left on for 3 weeks and then reset if needed. Hoof wall fractures typically result from blunt trauma, such as that induced by kicking a fence or wall. Similar to sole cracks, the wall crack is often contaminated and has serum leaking from the margins. As the underlying corium swells, some cracks may open more. With the foot
desensitized and a tourniquet applied if needed, the crack should first be stabilized with a 1 8-inch-thick aluminum plate (shoe) and acrylic. The wall is dried and sanded, and the plate is glued across the crack to stabilize it. Care should be taken to avoid covering the crack with adhesive glue and to maintain access to the entire crack. After the crack is stabilized and the acrylic has dried, the margins of the crack can be debrided with a Dremel3 tool and thoroughly cleaned. The repair is done first because the wall must be dry for the acrylic to adhere. If the bed of the crack is contaminated with debris, broad-spectrum systemic antimicrobials may be indicated to prevent infection. Radiographs should be taken to rule out other causes of distal interphalangeal joint pain, such as subchondral bone cysts of the joint.
3
Dremel, Robert Bosch Tool Co International.
Figure 183-14 Radiograph revealing fracture of the left lateral palmar process of the pedal bone in a foal.
Pedal Bone Fractures Foals can sustain any type of pedal bone fracture, but fractures of the palmar or plantar process of the pedal bone are the most common (Figure 183-14). The incidence of palmar process fractures in foals has been reported to range from 75% to as high as 100%. This type of fracture may be an incidental finding in a sound foal or a cause of severe lameness in other foals. Most foals in which the fracture causes clinical signs present with acute lameness that improves substantially after 24 hours of stall rest. These fractures typically heal with conservative treatment, such as restriction of exercise for 30 days or shoeing with return to routine turnout. A regular aluminum shoe glued to the foot for 3 to 4 weeks is typically sufficient. A true osseous union can be expected. Other fracture types are more serious and require more aggressive shoeing modalities along with exercise restriction to heal. More serious fractures include those involving the joint or those causing instability. In those cases, stabilization of the hoof capsule is required, along with arch or sole support to limit downward descent of the arch of the sole. Limiting pedal bone movement in all planes is the goal. This can be accomplished by gluing an aluminum shoe with a firm polyurethane or acrylic sole support to the hoof. Another option is to use a hoof-wall cast, applied with fiberglass casting tape. These stabilizing materials are changed every 3 to 4 weeks, and the fracture site should be monitored with radiographs to ensure healing. Foals heal faster than adult horses. Most foals take at least 3 months to heal. Fractures that involve the joint surface have a good prognosis for healing well, as long as the congruency of the joint surface is maintained.
Phalangeal Joint Pain Pain originating from the distal and proximal interphalangeal joints can occur in foals in which the hooves have been trimmed severely out of balance in an effort to correct an angular limb deformity. Such foals exhibit varying degrees of lameness, and a positive response to flexion of the distal joints of the limb can be expected. Occasionally, effusion of the distal interphalangeal joint can be palpated. Treatment is restoration of hoof balance, exercise restriction, and
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Figure 183-15 Rupture of the impar ligament in a foal. Notice the proximal displacement of the navicular bone.
systemic administration of nonsteroidal antiinflammatory drugs. Any foal with joint pain should be evaluated for septic arthritis by determination of body temperature, complete blood count and fibrinogen concentration, and arthrocentesis of the suspected septic distal interphalangeal joint. Other possible causes of distal interphalangeal joint pain include trauma to the joint or periarticular structures, or a subchondral bone cyst. However, most foals with subchondral bone cysts fail to show clinical lameness, and the lesion is not detected until a young horse is put into exercise, either as a yearling being prepared for sales or when it is beginning training as a 2-year-old.
Soft Tissue Injuries Rarely are soft tissue injuries diagnosed inside the foal hoof capsule, but with the use of magnetic resonance imaging these structures can be evaluated. Complete rupture of the impar ligament can be seen as a proximal displacement of the navicular bone in the foal (Figure 183-15). This can be caused by an acute injury or by overaggressive correction of phalangeal contracture.
Laminitis Laminitis is rare in the foal but has been reported. The lamellar epidermal-dermal attachment depends on the integrity of the basal cell cytoskeleton, hemidesmosomes, anchoring filaments, and basement membrane. Any genetic defect that affects the molecular components of this attachment can cause congenital laminitis in the foal. A defect in laminin 5 (anchoring filament protein) occurs in epidermolysis bullosa in Belgian foals and is the cause of skin sores and laminitis. Deficiency in plectin, a hemidesmosome protein, has been described in a Quarter Horse foal with congenital laminitis. In these conditions, laminitis can be seen in the front, hind, or all four feet. Foals can have the posture and gait classically associated with founder, that is, rocking backward and placing the front feet far out in front of the body. If the hind feet are affected, a goose-stepping or hypermetric gait is common. Physical examination reveals exaggerated digital pulse intensity, soreness to hoof testers over the toe region, and a flat or even prolapsed sole. Radiographs confirm
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displacement of the pedal bone (Figure 183-16). Congenital founder conditions carry a poor prognosis for future soundness. As body weight and size increase with age, these cases become increasingly difficult to manage. Laminitis of traumatic origin also occurs in foals. Traumatic laminitis or road founder can be seen in foals that must keep up with young dams that run excessively on firm footing or hard ground. These cases typically respond well to rest, administration of nonsteroidal antiinflammatory drugs, and foot support and protection. Mechanical tearing of the laminae can be a complication in the treatment of foals with flexor tendon contracture. Application of toe extensions to counter the tension of a contracted deep digital flexor tendon can mechanically tear the dorsal laminae. When wearing toe extensions, foals should be monitored daily for soreness or strong digital
pulses. Limb splints should therefore be used to stretch the tendons in foals with severe contractures. The latter treatment distributes countertension over more structures and greater surface area, whereas toe extensions apply forces to only the hoof and laminae to counter the tendon contraction. Treatment of laminitis in the foal should be directed toward reducing strain on the compromised laminae. Stall rest, combined with use of nonsteroidal antiinflammatory drugs and special shoeing, is the mainstay of treatment. Reducing the functional toe length or lever arm and facilitating breakover are methods of decreasing strain on the anterior laminae. The addition of axial or sole support materials such as silicone, urethane, and elastomers can be used to create loading of the sole and frog and take weight off the hoof wall. Severe cases of laminitis may need heel elevation to reduce tension on the deep digital flexor tendon, move the center of pressure toward the heels, and decrease strain in the toe region. Future prognosis depends on the degree of damage and quality of healing. Foals that develop a significant degree of bone demineralization or heal with a thickened lamellar interface (lamellar wedge) carry a less favorable prognosis for future soundness.
Polydactyly and Adactyly
Figure 183-16 Radiograph of the foot of a foal with congenital laminitis. Notice the displacement of the pedal bone within the hoof capsule.
A
B
Polydactyly refers to the congenital condition in which more than one digit (phalangeal bone) develops on a given limb. The digit can develop proximal to the fetlock and articulate with the second metacarpal or tarsal bone, or the digit can develop distal to the fetlock, in which the extra digit articulates with distal third metacarpal or tarsal bone. Polydactyly originating proximal to the fetlock can be treated successfully by surgical removal. When polydactyly involves articulation with the third metacarpal or tarsal bone, the prognosis for soundness is poor. Adactyly refers to the absence of an entire digit or one phalangeal bone (Figure 183-17). These cases typically present with a vestigial distorted hoof and contracted distal limb. Foals that are missing just the third phalanx can be pasture sound for a limited time if they have a functional hoof and the contracture is resolved, but they experience complications such as arthritis and recontracture as they age. Both these conditions are relatively rare.
C
Figure 183-17 A, Foal born with no pedal bone (adactyly) in the right hind limb. B and C, Same foal 3 months later. Notice the hoof and sole growth and ossification of the extensor process of the third phalanx (visible just above the hoof in B).
Suggested Readings Bowker RM. The growth and adaptive capabilities of the hoof wall and sole: functional changes in response to stress. In: Proceedings of the American Association of Equine Practitioners, 2003;49:146-168. Chan CC-H, Munroe GA. Congenital defects of the equine musculoskeletal system. Equine Vet Educ 1996;8:157-163. Compston PC, Payne RJ. Active tension-extension splints: a novel technique for the management of congenital flexural deformities affecting the distal limb in the foal. Equine Vet Educ 2011;24:209-306. Crow MW, Swerczek TW. Equine congenital defects. Am J Vet Res 1985;46:353-358. Dascanio JJ, Pleasant RS, Witonsky SG, et al. Palmar process fractures in foals: a prospective radiographic survey of the incidence and duration of fractures on a Virginia farm. In: Proceedings of the American Association of Equine Practitioners, 2009;55:238. French KR, Pollitt CC. Equine laminitis: congenital hemidesmosomal plectin deficiency in a Quarter Horse foal. J Am Vet Med Assoc 2004;36:299-303. Greet TRC. Managing flexural and angular limb deformities: the Newmarket perspective. In: Proceedings of the American Association of Equine Practitioners, 2000;46:130-136. Hartzel DK, Arnoczky SP, Kilfoyle SJ, et al. Myofibroblasts in the accessory ligament (distal check ligament) and the deep digital flexor tendon of foals. Am J Vet Res 2001;62:823-827. Kasper C, Clayton H, Wright A, et al. Effects of high doses of oxytetracycline on metacarpophalangeal joint kinematics in neonatal foals. J Am Vet Med Assoc 1995;207:71-73.
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Mayhew IG. Neuromuscular arthrogryposis multiplex congenita in a Thoroughbred foal. Vet Pathol 1984;21: 187-192. McIlwraith CW, Anderson TA, Douay P, et al. Role of conformation in musculoskeletal problems in the racing Thoroughbred and racing Quarter Horse. In: Proceedings of the American Association of Equine Practitioners, 2003;49: 59-61. McIlwraith CW, James LF. Limb deformities in foals associated with ingestion of locoweed by mares. J Am Vet Med Assoc 1982;72:293-298. Morgan JW, Leibsle SR, Gotchey MH, et al. Forelimb conformation of Thoroughbred racing prospects and racing performance from 2 to 4 years of age. In: Proceedings of the American Association of Equine Practitioners, 2005;51: 299-300. Morrison SM. How to utilize sterile maggot debridement therapy for infections of the horse. In: Proceedings of the American Association of Equine Practitioners, 2005;51-54. Munroe GA, Chan CC-H. Congenital flexural deformities of the foal. Equine Vet Educ 1996;8:92-96. Pierce SW. Foal care from birth to 30 days: a practitioner’s perspective. In: Proceedings of the American Association of Equine Practitioners, 2003;49:13-21. Smith LJ, Marr CM, Payne RJ, et al. What is the likelihood foals treated for septic arthritis will race? Equine Vet J 2004;36:452-456. Wilsher S, Ousey J, Allen WR. Observations on the placentae of eight Thoroughbred foals born with flexural limb deformities. Equine Vet Educ 2013;25:84-95.
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he newborn foal can be affected by many congenital and acquired conditions that influence normal limb function and ambulation. Of all congenital deformities in the foal, congenital musculoskeletal abnormalities are the most common, with flexural and angular deformities being the most frequent congenital causes of lameness. However, not all congenital musculoskeletal deformities will cause lameness in the foal, and some may not become clinically evident until the foal matures and begins training. Acquired conditions in the newborn foal are a response to an event that occurs shortly after birth.
CONTRACTURES
Contractures are congenital conditions that typically affect bigger foals, but they can be seen in all body types. They range from upright fetlocks and pasterns to being over at the knee to severe deformities resulting in loss of use of the limb. One or more limbs can be affected, and the contracture can involve the deep digital or superficial flexor tendon, the suspensory ligament, the joint capsules, or any combination thereof. In foals with deep digital flexor tendon contracture, also known as ballerina syndrome, the heel does not contact the ground, and the foal walks on the toe or dorsal hoof wall. In severe bilateral cases, the foal is unable to stand. With superficial flexor tendon contracture, in contrast, the foot can be placed flat on the ground, but the fetlock and pastern buckle forward (Figure 183-1).
Etiology The cause of tendon contracture is unknown. Spatial restriction on the growth of large foals in utero is a theory commonly proposed to explain development of contractures, and in support of this was the finding in one study that the placentas of eight Thoroughbred foals with limb contractures were smaller than those of normal foals. There seems to be no correlation between the incidence of contractures and mare age, and the condition does not seem to be inherited. Because flexural deformities seem to be more common in some years than others and appear to come in groups, toxins (locoweed, Sudan grass, iodide toxicosis, or goiter) and influenza infection have been implicated, possibly by causing neuromuscular disorders in the developing limb. Bilateral limb contractures may be part of a larger complex known as contracted foal syndrome, which encompasses multiple developmental disorders, including bilateral limb contracture, torticollis, scoliosis, asymmetry of the skull, and attenuation or thinning of the ventral abdominal wall with possible eventration.
Treatment Treatment of appendicular contractures consists of medical treatment with oxytetracycline (3 g diluted in 150 mL saline solution and given intravenously over 10 minutes, once daily
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for 3 days) combined with mechanical stretching of the contracture with splints, braces, or both. Some degree of pain and discomfort can be expected from the splinting process, and administration of antiinflammatory drugs and antiulcer medication should be considered. Contractures become progressively harder to treat successfully with age. For this reason, treating affected foals early and aggressively is imperative; ideally, these foals are evaluated and treated on the first day of life. The typical newborn foal is sedated with intravenously administered butorphanol (3 mg) combined with xylazine (30 mg) and placed in lateral recumbency in the stall with the eyes covered by a towel. The limb is bandaged with a cotton combine bandage or quilt to the full extent of the contracture. For distal interphalangeal and fetlock contractures, the bandage is applied from the hoof to the proximal part of the cannon bone. For carpal contractures, the limb is bandaged from the cannon bone to the elbow. If the contractures extend from the distal interphalangeal joint through the fetlock and carpus, the bandage must also extend from hoof to elbow. The cotton combine bandage must be firmly secured with Vetrap1 or a similar product. The limb is held in extension, and a 3- or 4-inch-wide roll of fiberglass casting material is unrolled, folded to the length of the bandage, and applied to the palmar or plantar aspect of the limb. While the contracted joints are held in extension by direct manual pressure on the dorsum of the involved joints, the cast splint is bandaged to the limb with adhesive bandaging tape. Care should be taken not to bandage the splint to the limb too tightly or create a wrinkle in the splint material to avoid creating pressure points and skin sores. The pressure and forced extension are held until the cast has set. If the distal interphalangeal joint is involved, the cast splint must be extended to under the solar surface of the foot and at least one third of the way up the dorsal wall of the hoof (Figure 183-2). When the carpus is contracted, care should be taken not to bandage the splint too tightly in the antebrachial region because this can cause radial nerve paralysis. The splint is usually changed daily, making a new splint and achieving more correction each time. Most cases can be corrected within 3 to 4 days. Foals in which more than one limb is involved may need assistance to stand and nurse. After the limb contracture is corrected with splinting, the leg is maintained in a bandage for a few days to gradually decrease the level of support, and the foal is slowly introduced to turnout and exercise. In the author’s experience, a proportion of these foals will appear normal for a couple of months and then slowly develop an acquired club foot in one of the limbs. For this reason, cases of contracture should be closely monitored throughout their growth and
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Vetrap, 3M.
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183 Lameness in Foals
C
Figure 183-1 Foals with tendon contractures. Contracture of the deep digital flexor tendon in the left hind limb (A); contracture of the superficial flexor tendon before (B) and after (C) splinting for 3 days.
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B Figure 183-2 A, Splinting technique for deep digital flexor tendon contracture of the right forelimb. The foal is lying in left lateral recumbency (hoof is to the left). The bandages are applied around the limb, and the casting tape is being applied along the long axis of the limb. B, In this foal, the right hind limb is in a splint cast that is protected with a bandage.
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XVI The Foal safer to address these cases with bandages and splints, because these methods distribute the stress over a larger area. When toe extensions are used in mild cases, the foal should be monitored daily for lameness, which may indicate lamellar tearing. In those instances, the extension must be removed. In lame foals that have pain in the toe region, radiographs should be taken to rule out mechanical laminitis.
FLEXOR TENDON LAXITY
Figure 183-3 A toe extension (toe reinforcement) applied to a congenital club foot. The toe extension is made with an acrylic and fiberglass fabric compound.
Figure 183-4 Close-up of view of a shear lesion at the anterior coronary band of the hind foot of a foal that had a heel extension shoe placed too early in life.
development. Many of these foals eventually become sound athletes. Slight deep digital flexor tendon contracture may respond to stall rest, bandaging, and administration of antiinflammatory drugs. If the toe length is short or is being worn excessively, a toe extension may provide more leverage to lower the heel and stretch the contracted tendon (Figure 183-3). These toe extensions should, however, be used with caution because when they are applied, only a small area of the hoof is being used to counter and correct the contracture. Excessive strain concentrated on the immature toe region can cause tearing of the pedal bone away from the hoof wall, laminitis, or both. Because some cases can develop separation of the anterior part of the coronary band or shear lesion (Figure 183-4), shoes or toe extensions should not be applied within the first week of life, when the soft immature hoof and lamellar interface are more prone to failure. It is much
Laxity of the flexor tendons is another congenital condition that typically is seen in dysmature or premature foals, but the condition also occurs in otherwise normal foals. Flexor tendon laxity can affect one or more limbs but usually occurs in the hind limbs (Figure 183-5). The laxity and associated hyperextension commonly involve the phalangeal and metacarpal or metatarsal joints. Some cases also have hyperextension of the carpus or hyperflexion of the tarsus; such animals are said to be “back at the knee” or “sickle hocked,” respectively. Most of these foals improve within the first week of life. Many are also born with excessive hoof growth, so trimming the feet removes toe length, moves the heel position caudally, helps decrease the hyperextension of the distal interphalangeal joint, and helps prevent the toe from turning upward (Figure 183-6). Foals with flexor tendon laxity should be managed with stall rest and controlled exercise, such as hand walking the mare in the barn aisle several times daily while the foal follows. After the muscles and tendons strengthen, the mare and foal can begin turnout into a small paddock. Foals that are back at the knee or sickle hocked should not be allowed to exercise before radiographs have been taken to ensure that the carpal and tarsal bones are fully ossified; crushing of the incompletely ossified carpal or tarsal bones can create permanent wedge-shaped cuboidal bones and lameness. In foals that do not improve within a week or that develop heel bulb ulcerations, heel extensions can help provide caudal leverage and force the toe onto the ground. Heel extensions are usually cuffed shoes, which are attached to the hoof wall with epoxy or acrylic adhesive. These shoes are typically left on for 10 to 14 days, after which the hoof is trimmed and the foal is reevaluated. It is important not to attach the cuff to the heel region of the foot because the area is under stress and easily pinched or bruised by the glue. For this reason, the cuffed shoe should be modified by cutting the cuff away from the back half of the hoof and leaving cuff only to be attached to the toe of the hoof. After the cuff has been on for 5 days, the heel extension can be shortened by 50% with hoof nippers. After another 5 to 9 days, the shoe will need to be removed and the hoof trimmed. Most foals will have strengthened by this time and can be left barefoot. Some may require a second shoe application. If possible, the limbs of foals with tendon laxity should not be bandaged because the additional support causes further relaxation of the tendons and ligaments, worsening the laxity. If a bandage is required to protect an ulcerated area or sore on the fetlock or heel bulb, it should be loosely applied to just that area and not extended up the limb. The occasional foal with severe laxity is unresponsive to treatment (Figure 183-7).
ANGULAR DEFORMITIES
Angular deformities can be congenital or acquired and are common in the newborn foal. They are classified as valgus or varus according to whether the limb deviation is lateral or medial to the axis of limb, respectively. Foals with mild deformities are often sound, but those with more severe angular deformities can be lame because the limb instability
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over the medial or lateral region of the growth plate, which is sometimes referred to as physitis. Angular deformities can be classified as articular, diaphyseal, or physeal in origin. If the deformity can be straightened manually, it is the result of an articular deformity, which can be the consequence of incomplete ossification (usually the carpus or hock), uterine malpositioning, or flaccidity of the periarticular structures. Articular deformities respond well to rest, time, and application of some external form of support such as bandaging and splinting, if the angulation is severe. If incomplete ossification goes unnoticed, it can result in permanent deformity by the time the foal is several weeks old. Diaphyseal angular deformities are less common and originate along the diaphysis of the bone, giving the bone a bowed appearance. Physeal angular deformities are the result of congenital or acquired asymmetric growth of the metaphysis or epiphysis.
A
B
C Figure 183-5 Hind feet of a foal with flexor tendon laxity. A, The foal is resting on the bulbs of the heels, which results in development of heel bulb ulcers (B). C, A heel extension shoe has been glued to the foot. Notice how the cuff is trimmed away from the heel region so that it is only adherent to the toe region.
and abnormal loading of joints causes joint instability, physitis, and abnormal or excessive hoof wear. The normal newborn foal should have a moderate degree of carpal, tarsal, and fetlock joint valgus conformation and slight outward rotation of all four limbs (Figure 183-8). As long as the loading forces on the physis are within the normal physiologic range of the physeal cartilage, most valgus deformities improve with time. This is because physeal cartilage growth increases in response to compressive forces. However, if angular deformities are more severe and compressive forces are excessive, physeal growth slows. Foals with excessive compressive forces usually develop signs of pain and swelling
Treatment Treatment of angular deformities depends on severity, location, and how the joint angles change over time. The two main areas of interest with regard to managing the foot are the physis of the distal metacarpus or metatarsus and the physis of the distal radius. The management and treatment goals are to prevent and correct the excessive angular deformities or those that will create excessive compression on the growth plate and retard normal corrective physeal growth. Any varus deformity, and an excessive degree of valgus deformity, is abnormal. Constant improvement or self-correction is the desired trend in response to treatment. Frequent monitoring of the foal is paramount for early detection of limbs that are not improving with time so that proper intervention can be implemented to help correct the deformity. An understanding of the tools available and limitations of each is necessary to effectively implement a foal foot management plan. Equally as important as foot care is recognizing which limb abnormalities will respond favorably to foot manipulations and which may necessitate other treatment modalities, such as transphyseal bridge surgery. Distal metacarpal or metatarsal angular deformities (fetlock varus or fetlock valgus) are common. Because foot manipulations have most influence on the distal part of the limb and less influence proximally, fetlock angular deformities are most likely to respond to foot trimming or shoeing. Distal physes in the metacarpal and metatarsal bones close by 4 to 5 months and lose 50% of their growth potential every 30 days up to that time. Consequently, it is imperative that fetlock angular limb deformity be appropriately managed at an early age. The goal is to maintain the center of the foot directly perpendicular to the upright cannon bone (imagine a plumb line dropped through the center of the cannon bone to the center of the foot) while ignoring the angulation of the carpus or tarsus. One of the most common mistakes made in treatment of angular deformities is trying to correct a carpal angular deformity by use of foot manipulations at an early age and in the process worsening or creating a fetlock angular deformity. For this reason, emphasis should be on establishing fetlock alignment during the first 3 to 4 months and then, after the distal metacarpal or metatarsal physis has closed, shifting the focus to the carpus because the distal radial physis does not close physiologically until 14 months of age. Valgus deformities of the fetlock usually improve with time and typically do not require treatment unless severe. Fetlock varus, on the other hand, generally does not improve with time and requires trimming, application of shoe extensions, or surgical correction.
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C
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D
Figure 183-6 A, A newborn foal foot with mild flexor tendon laxity, which results in the weight being borne on the heels. Trimming away the excessive hoof tissue to move the heel position caudally (B and C) resulted in a more normal posture (D).
Trimming alone can be effective in treating mild angular deformities of the fetlock region. If, however, the selfcorrecting mechanism is failing to improve the angular deformity, then one must assume that the medial region of the physis in a varus deformity or the lateral aspect of the physis in a valgus deformity is overloaded and growth is decreased in that region of the physis. Trimming and shoeing techniques to help decrease compressive forces on the medial or lateral region of the physis can alter physeal growth and encourage straightening of the limb. For example, lowering the medial side of the foot will decrease compression on the medial aspect of the bone column and increase compression laterally. Decreasing the height of the hoof wall on one side of the limb increases compressive force on the contralateral, longer side and creates tension on the “short” side of the foot, bone column, and physis. Additionally, lowering one side of the foot changes the manner in which the foot strikes the ground and becomes loaded: the longer side of the hoof strikes the ground first, causing the limb to align closer to the long side of the hoof. This potentially encourages loading on the longer side. If the trim alone aligns the foot with the
center of the cannon bone, trimming every 2 to 3 weeks may be sufficient to correct the angular deformity. Care should be taken when trimming foals’ feet. Overtrimming will cause bruising, wing fractures, and lameness. The foot should be routinely examined by digital palpation, and during the trim, as much sole as possible should be left in place for protection. Rolling the edge of the hoof wall can provide some degree of correction without invading sole mass. If the desired foot position cannot be achieved with the trim alone, application of a hoof extension is required. Shoes are recommended in foals that require more than 1 cm of correction and in those that become footsore from corrective trimming. Shoes provide correction while protecting the sole and do not cause focal tearing in one region of the hoof wall (Figure 183-9). If a fetlock deformity does not improve by 60 days and is severe, surgical placement of a transphyseal bridge may be indicated. Carpal deformities should be graded on that basis of severity. Slight (2 to 5 degrees) carpal valgus is normal in newborn foals of good conformation, and most cases of carpal valgus improve within 30 days. Surgical intervention may be
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indicated if the deformity stops improving or changes for the worse. Careful monitoring and scoring of the deformity is therefore important. In foals with severe carpal deformity, carpal radiographs should be taken to evaluate the cuboidal bones. Delayed ossification of the cuboidal bones makes enforced stall rest necessary until the bones have matured. If, however, there
183 Lameness in Foals
is angular deformity but the cuboidal bones are mature, the foal can be turned out for short periods. Shoes with medial extensions can be helpful in managing carpal valgus deformities, but care should be taken to not create a fetlock varus deformity in the process. This is especially important during the first 4 to 5 months of age (Figure 183-10). When a shoe is applied for a carpal angular deformity, the foot should be trimmed and balanced so that it is centered more perpendicular to the long axis of the cannon bone, with an extension used to support the carpal deformity. Unlike with fetlock angular deformities, altering hoof length medial to lateral is unlikely to have a significant beneficial effect on the physis of the upper limb and will only unnecessarily distort the hoof. Windswept foals have a conformational abnormality in which one limb has a varus deformity and the opposite limb has a valgus deformity. This condition can occur in the forelimbs or hind limbs. The condition will self-correct with time and does not warrant surgical intervention. The foot should be trimmed and balanced. If the hoof is rolling over on the medial aspect of the valgus limb or the lateral aspect of the varus limb, a shoe with a medial extension (for the valgus limb) or a lateral extension (for the varus limb) can be applied to help direct and support the foot directly beneath the bone column.
ROTATIONAL DEFORMITIES
Figure 183-7 A foal with severe hind limb flexor tendon laxity that failed to improve after 30 days of controlled exercise and use of heel extensions.
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B
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Newborn foals normally have slight outward rotation of the limbs, but this improves as the muscles of the chest and hindquarters develop. Rotational deformities that originate high in the limb are likely to improve with time. Rotational deformities that originate distal to the carpus generally do not improve. The author does not recommend correction of a rotational deformity by trimming and shoeing. The foot should be trimmed such that it is maintained directly beneath the cannon bone when viewed directly in front of the dorsal surface of that limb. Trying to correct a rotational deformity by trimming or shoeing the foot usually adds a fetlock
C
Figure 183-8 A foal with carpal valgus that improved over 6 weeks without treatment. Images show foal at 1 (A), 6 (B), and 9 (C) weeks of age.
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TRAUMATIC INJURIES OF THE FOOT Examination of the Foot
Figure 183-9 Foot extension of the type used when desired foot position cannot be achieved by trimming alone or when the foal requires more than 1 cm of correction. Notice the physitis of the distal metacarpus and the proximal phalanx.
In foals, common causes of acute-onset lameness are sole bruising, pedal bone fractures, and local infections. Diagnosis begins with examination of the foal at a walk and trot, if necessary. It is helpful to watch the foal walk or trot freely while the mare is led. When young foals are led, they often lean into or away from the holder, making gait evaluation difficult. After the lame limb is identified, thorough evaluation of the foot is performed. The foot should be cleaned and brushed out. The coronary band, heel bulbs, and pastern should be palpated for pain or swelling. The lame foot will have an exaggerated digital pulse. Examination with hoof testers will help locate the area of soreness. Because most foals will give false-positive responses to application of hoof testers, mild sedation will help improve the accuracy of the hoof-tester examination. A repeatable response to gentle hoof-tester pressure is considered a positive response. The coffin and pastern joints are flexed and palpated for pain, heat, or effusion. Diagnostic nerve blocks can help confirm the foot as the source of lameness. When the area of soreness is located, the foot is trimmed and closely inspected for defects in the sole or white line.
Bruising of the Foot Bruising of the foot is typically diagnosed by ruling out other causes of foot lameness. Bruises typically improve with time. Bandaging or applying a poultice to the foot, stall rest, and use of nonsteroidal antiinflammatory medications can speed recovery. Severe bone contusions, which can be confirmed by magnetic resonance imaging, can take longer to resolve.
Local Infections
Figure 183-10 Right front carpal valgus with fetlock varus conformation. The fetlock varus was caused by trying to correct the carpal valgus through trimming and shoeing.
angular deformity to the preexisting rotational deformity. Some practitioners advocate the use of a medial toe extension to force the foot to breakover at its center and to prevent it from breaking over on the medial quarter. This treatment does not correct the rotational deformity, but rather, the hoof capsule will develop a twisted or distorted appearance, or wry foot. The offset or “bench” knee conformation is an axial deformity in which the carpus is offset laterally to the metacarpus. This places more stress on the medial aspect of both the
If the lameness worsens with time, an infection should be considered. Most abscesses are detected through close inspection of the sore area of the foot. Defects in the sole, frog, or white line should be carefully debrided and trimmed out or followed down to the site of infection. The abscess should be adequately opened to allow drainage and prevent premature closure of the hole. A small double-edged abscess knife or a bone curette is useful for the latter procedure. If the infection cannot be located, an overnight poultice can be applied to the foot to encourage the abscess to mature. The poultice can be a wet Animalintex2 pad or other poultice product bandaged to the foot. The foal should be noticeably improved within the 2 days following abscess drainage. If the lameness persists without improvement or if drainage continues for more than 3 days, radiographs should be taken to evaluate the health of the pedal bone. Septic osteitis of the pedal bone is typically evident on radiographs within 3 to 5 days of onset of infection at the site. Septic osteitis of the pedal bone is seen as a focal irregular demineralization of the solar margin with gas or fluid opacities (Figure 183-11). Larger areas of infection may have larger areas of demineralization or sequestrum formation. Some cases may take longer to become evident radiographically, so if lameness persists, radiographs should be repeated as needed. Pedal bone septic osteitis warrants culture and
2
Animalintex Poultice Pad, 3M.
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B
Figure 183-11 Radiographs of two cases of septic pedal osteitis. A, Small focal area of osteomyelitis at the toe region of the pedal bone. B, Large area of osteomyelitis at the toe region of the pedal bone.
antimicrobial sensitivity testing. Treatment involves surgical debridement, administration of systemic antimicrobials, and possibly regional limb perfusion (see Chapter 186). Focal areas of septic osteitis can be effectively treated with medicalgrade larval therapy (also referred to as maggot therapy) and systemic antimicrobials.
Puncture Wounds Puncture wounds of the foot can be difficult to detect and inspect because tracts close quickly in the very elastic and pliable foal hoof. If a puncture to the sole or frog is suspected, the sore area should be pared down and gently inspected with a blunt-tipped, malleable probe. This part of the examination is usually performed with the foal under sedation and the foot desensitized with an abaxial sesamoid nerve block. When the tract is identified, the foot should be scrubbed and prepared for deeper inspection and a fistulogram. Deeper inspection includes probing the tract to determine the depth and direction of the wound. The fistulogram identifies the extent of the infection and involvement of synovial structures (Figure 183-12). It is performed by injecting 5 mL of radiopaque contrast material through a tomcat or 18-gauge, 3-inch catheter that has been inserted into the tract as far as it will go. The contrast material will leak out of the tract and onto the external surface of the sole and hoof and should be wiped off with alcohol-soaked gauze before the foot is placed on a radiograph block. Lateral and horizontal anterior-posterior views are taken. Suspected synovial infection detected on the fistulogram can be confirmed by arthrocentesis. Sepsis of a synovial structure (phalangeal joint, tendon sheath, or navicular bursa) requires aggressive daily lavage of the involved structures, regional limb antimicrobial
perfusions, and systemic broad-spectrum antimicrobials. Synovial fluid samples should be submitted for determination of the leukocyte count and total protein concentration and for bacterial culture. The foal’s comfort level, the leukocyte count of the synovial fluid retrieved before each lavage, and serum analyte concentration are the most common methods used to monitor progression of the infection. Daily lavage is recommended until the cell counts are normal and the foal is walking well. If lameness worsens after cessation of the lavage, centesis and white blood cell count should be repeated.
Injuries to the Hoof Capsule Injuries to the hoof wall, such as wall avulsions and fractures of the wall, sole, or pedal bone, are common and can result from kicking a fence or wall, stepping on a rock, or being stepped on by the mare. All traumatic injuries of the foot should be examined and radiographed to assess for involvement of deeper structures. With the foal sedated and the foot desensitized, the area of wall damage should be soaked, scrubbed, and disinfected. If the lesion is bleeding profusely, it may be helpful to apply a tourniquet. If the avulsion involves only the hoof capsule and the underlying corium is not damaged, the detached wall can be debrided and cut away. The exposed corium should be dressed with povidone-iodine solution or povidone cream and a heavily padded bandage. If the wall detachment involves more than one third of the hoof wall, a foot cast may be needed to stabilize the compromised hoof and improve comfort. The first foot cast should be changed in 3 to 4 days, then every 2 weeks thereafter until the hoof becomes cornified (Figure 183-13). If the avulsion involves deep lacerations to the coronet or pastern, surgical repair and
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B
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Figure 183-12 Three examples of fistulograms from horses with puncture wounds of the hoof. A, Frog puncture wound with involvement and communication with tendon sheath. B, Anterior coronary band puncture wound with distal interphalangeal joint involvement. C, Wire puncture wound showing no synovial structure involvement.
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B
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Figure 183-13 Hoof avulsion in a foal. The foot is shown immediately after wall avulsion (A), after 2 weeks of foot casting (B), and after 4 months (C).
sutures are required for the best result and to prevent abnormal coronary band wall growth. Sole fractures are the result of kicking or stepping on a firm object. Acute lameness and a cracked sole are seen on examination. Serum discharge is often seen on the margins of the sole crack. The bed of the crack is often contaminated with debris. Opening the margins of the crack, debriding the bed of the crack, and soaking and cleansing the defect are recommended. Applying a shoe with a removable treatment plate helps suspend and protect the damaged sole. This improves the lameness immediately and speeds recovery. The shoe is left on for 3 weeks and then reset if needed. Hoof wall fractures typically result from blunt trauma, such as that induced by kicking a fence or wall. Similar to sole cracks, the wall crack is often contaminated and has serum leaking from the margins. As the underlying corium swells, some cracks may open more. With the foot
desensitized and a tourniquet applied if needed, the crack should first be stabilized with a 1 8-inch-thick aluminum plate (shoe) and acrylic. The wall is dried and sanded, and the plate is glued across the crack to stabilize it. Care should be taken to avoid covering the crack with adhesive glue and to maintain access to the entire crack. After the crack is stabilized and the acrylic has dried, the margins of the crack can be debrided with a Dremel3 tool and thoroughly cleaned. The repair is done first because the wall must be dry for the acrylic to adhere. If the bed of the crack is contaminated with debris, broad-spectrum systemic antimicrobials may be indicated to prevent infection. Radiographs should be taken to rule out other causes of distal interphalangeal joint pain, such as subchondral bone cysts of the joint.
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Dremel, Robert Bosch Tool Co International.
Figure 183-14 Radiograph revealing fracture of the left lateral palmar process of the pedal bone in a foal.
Pedal Bone Fractures Foals can sustain any type of pedal bone fracture, but fractures of the palmar or plantar process of the pedal bone are the most common (Figure 183-14). The incidence of palmar process fractures in foals has been reported to range from 75% to as high as 100%. This type of fracture may be an incidental finding in a sound foal or a cause of severe lameness in other foals. Most foals in which the fracture causes clinical signs present with acute lameness that improves substantially after 24 hours of stall rest. These fractures typically heal with conservative treatment, such as restriction of exercise for 30 days or shoeing with return to routine turnout. A regular aluminum shoe glued to the foot for 3 to 4 weeks is typically sufficient. A true osseous union can be expected. Other fracture types are more serious and require more aggressive shoeing modalities along with exercise restriction to heal. More serious fractures include those involving the joint or those causing instability. In those cases, stabilization of the hoof capsule is required, along with arch or sole support to limit downward descent of the arch of the sole. Limiting pedal bone movement in all planes is the goal. This can be accomplished by gluing an aluminum shoe with a firm polyurethane or acrylic sole support to the hoof. Another option is to use a hoof-wall cast, applied with fiberglass casting tape. These stabilizing materials are changed every 3 to 4 weeks, and the fracture site should be monitored with radiographs to ensure healing. Foals heal faster than adult horses. Most foals take at least 3 months to heal. Fractures that involve the joint surface have a good prognosis for healing well, as long as the congruency of the joint surface is maintained.
Phalangeal Joint Pain Pain originating from the distal and proximal interphalangeal joints can occur in foals in which the hooves have been trimmed severely out of balance in an effort to correct an angular limb deformity. Such foals exhibit varying degrees of lameness, and a positive response to flexion of the distal joints of the limb can be expected. Occasionally, effusion of the distal interphalangeal joint can be palpated. Treatment is restoration of hoof balance, exercise restriction, and
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Figure 183-15 Rupture of the impar ligament in a foal. Notice the proximal displacement of the navicular bone.
systemic administration of nonsteroidal antiinflammatory drugs. Any foal with joint pain should be evaluated for septic arthritis by determination of body temperature, complete blood count and fibrinogen concentration, and arthrocentesis of the suspected septic distal interphalangeal joint. Other possible causes of distal interphalangeal joint pain include trauma to the joint or periarticular structures, or a subchondral bone cyst. However, most foals with subchondral bone cysts fail to show clinical lameness, and the lesion is not detected until a young horse is put into exercise, either as a yearling being prepared for sales or when it is beginning training as a 2-year-old.
Soft Tissue Injuries Rarely are soft tissue injuries diagnosed inside the foal hoof capsule, but with the use of magnetic resonance imaging these structures can be evaluated. Complete rupture of the impar ligament can be seen as a proximal displacement of the navicular bone in the foal (Figure 183-15). This can be caused by an acute injury or by overaggressive correction of phalangeal contracture.
Laminitis Laminitis is rare in the foal but has been reported. The lamellar epidermal-dermal attachment depends on the integrity of the basal cell cytoskeleton, hemidesmosomes, anchoring filaments, and basement membrane. Any genetic defect that affects the molecular components of this attachment can cause congenital laminitis in the foal. A defect in laminin 5 (anchoring filament protein) occurs in epidermolysis bullosa in Belgian foals and is the cause of skin sores and laminitis. Deficiency in plectin, a hemidesmosome protein, has been described in a Quarter Horse foal with congenital laminitis. In these conditions, laminitis can be seen in the front, hind, or all four feet. Foals can have the posture and gait classically associated with founder, that is, rocking backward and placing the front feet far out in front of the body. If the hind feet are affected, a goose-stepping or hypermetric gait is common. Physical examination reveals exaggerated digital pulse intensity, soreness to hoof testers over the toe region, and a flat or even prolapsed sole. Radiographs confirm
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displacement of the pedal bone (Figure 183-16). Congenital founder conditions carry a poor prognosis for future soundness. As body weight and size increase with age, these cases become increasingly difficult to manage. Laminitis of traumatic origin also occurs in foals. Traumatic laminitis or road founder can be seen in foals that must keep up with young dams that run excessively on firm footing or hard ground. These cases typically respond well to rest, administration of nonsteroidal antiinflammatory drugs, and foot support and protection. Mechanical tearing of the laminae can be a complication in the treatment of foals with flexor tendon contracture. Application of toe extensions to counter the tension of a contracted deep digital flexor tendon can mechanically tear the dorsal laminae. When wearing toe extensions, foals should be monitored daily for soreness or strong digital
pulses. Limb splints should therefore be used to stretch the tendons in foals with severe contractures. The latter treatment distributes countertension over more structures and greater surface area, whereas toe extensions apply forces to only the hoof and laminae to counter the tendon contraction. Treatment of laminitis in the foal should be directed toward reducing strain on the compromised laminae. Stall rest, combined with use of nonsteroidal antiinflammatory drugs and special shoeing, is the mainstay of treatment. Reducing the functional toe length or lever arm and facilitating breakover are methods of decreasing strain on the anterior laminae. The addition of axial or sole support materials such as silicone, urethane, and elastomers can be used to create loading of the sole and frog and take weight off the hoof wall. Severe cases of laminitis may need heel elevation to reduce tension on the deep digital flexor tendon, move the center of pressure toward the heels, and decrease strain in the toe region. Future prognosis depends on the degree of damage and quality of healing. Foals that develop a significant degree of bone demineralization or heal with a thickened lamellar interface (lamellar wedge) carry a less favorable prognosis for future soundness.
Polydactyly and Adactyly
Figure 183-16 Radiograph of the foot of a foal with congenital laminitis. Notice the displacement of the pedal bone within the hoof capsule.
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Polydactyly refers to the congenital condition in which more than one digit (phalangeal bone) develops on a given limb. The digit can develop proximal to the fetlock and articulate with the second metacarpal or tarsal bone, or the digit can develop distal to the fetlock, in which the extra digit articulates with distal third metacarpal or tarsal bone. Polydactyly originating proximal to the fetlock can be treated successfully by surgical removal. When polydactyly involves articulation with the third metacarpal or tarsal bone, the prognosis for soundness is poor. Adactyly refers to the absence of an entire digit or one phalangeal bone (Figure 183-17). These cases typically present with a vestigial distorted hoof and contracted distal limb. Foals that are missing just the third phalanx can be pasture sound for a limited time if they have a functional hoof and the contracture is resolved, but they experience complications such as arthritis and recontracture as they age. Both these conditions are relatively rare.
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Figure 183-17 A, Foal born with no pedal bone (adactyly) in the right hind limb. B and C, Same foal 3 months later. Notice the hoof and sole growth and ossification of the extensor process of the third phalanx (visible just above the hoof in B).
Suggested Readings Bowker RM. The growth and adaptive capabilities of the hoof wall and sole: functional changes in response to stress. In: Proceedings of the American Association of Equine Practitioners, 2003;49:146-168. Chan CC-H, Munroe GA. Congenital defects of the equine musculoskeletal system. Equine Vet Educ 1996;8:157-163. Compston PC, Payne RJ. Active tension-extension splints: a novel technique for the management of congenital flexural deformities affecting the distal limb in the foal. Equine Vet Educ 2011;24:209-306. Crow MW, Swerczek TW. Equine congenital defects. Am J Vet Res 1985;46:353-358. Dascanio JJ, Pleasant RS, Witonsky SG, et al. Palmar process fractures in foals: a prospective radiographic survey of the incidence and duration of fractures on a Virginia farm. In: Proceedings of the American Association of Equine Practitioners, 2009;55:238. French KR, Pollitt CC. Equine laminitis: congenital hemidesmosomal plectin deficiency in a Quarter Horse foal. J Am Vet Med Assoc 2004;36:299-303. Greet TRC. Managing flexural and angular limb deformities: the Newmarket perspective. In: Proceedings of the American Association of Equine Practitioners, 2000;46:130-136. Hartzel DK, Arnoczky SP, Kilfoyle SJ, et al. Myofibroblasts in the accessory ligament (distal check ligament) and the deep digital flexor tendon of foals. Am J Vet Res 2001;62:823-827. Kasper C, Clayton H, Wright A, et al. Effects of high doses of oxytetracycline on metacarpophalangeal joint kinematics in neonatal foals. J Am Vet Med Assoc 1995;207:71-73.
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Mayhew IG. Neuromuscular arthrogryposis multiplex congenita in a Thoroughbred foal. Vet Pathol 1984;21: 187-192. McIlwraith CW, Anderson TA, Douay P, et al. Role of conformation in musculoskeletal problems in the racing Thoroughbred and racing Quarter Horse. In: Proceedings of the American Association of Equine Practitioners, 2003;49: 59-61. McIlwraith CW, James LF. Limb deformities in foals associated with ingestion of locoweed by mares. J Am Vet Med Assoc 1982;72:293-298. Morgan JW, Leibsle SR, Gotchey MH, et al. Forelimb conformation of Thoroughbred racing prospects and racing performance from 2 to 4 years of age. In: Proceedings of the American Association of Equine Practitioners, 2005;51: 299-300. Morrison SM. How to utilize sterile maggot debridement therapy for infections of the horse. In: Proceedings of the American Association of Equine Practitioners, 2005;51-54. Munroe GA, Chan CC-H. Congenital flexural deformities of the foal. Equine Vet Educ 1996;8:92-96. Pierce SW. Foal care from birth to 30 days: a practitioner’s perspective. In: Proceedings of the American Association of Equine Practitioners, 2003;49:13-21. Smith LJ, Marr CM, Payne RJ, et al. What is the likelihood foals treated for septic arthritis will race? Equine Vet J 2004;36:452-456. Wilsher S, Ousey J, Allen WR. Observations on the placentae of eight Thoroughbred foals born with flexural limb deformities. Equine Vet Educ 2013;25:84-95.