Equine medicine my report


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Equine medicine my report

  1. 1. Lameness in Horses Lameness is defined as an abnormal stance or gait caused by either a structural or a functional disorder of the locomotor system. The horse is either unwilling or unable to stand or move normally. Lameness is the most common cause of loss of use in horses. It can be caused by trauma, congenital or acquired disorders, infection, metabolic disorders, and nervous and circulatory disease. Lameness is not a disease per se but a clinical sign. It is a manifestation of pain, mechanical restrictions causing alteration of stance or gait, or neuromuscular disease. Pain is the most common cause of lameness in all horses. The signs are most obvious at the walk. Pain-related lameness can be classified as weight bearing (supporting leg) or nonweight bearing (swinging leg) lameness. A supporting leg lameness is seen when the horse reduces the amount of time or reduces the amount of force applied to the weight-bearing limb. The most consistent and easily recognized clinical signs of lameness are the head nod associated with forelimb lameness and the sacral rise, also called a pelvic rise or hip hike, associated with hindlimb lameness. Factors that predispose horses to lameness include physical immaturity, which may occur in premature or dysmature foals, and training older foals prior to maturity. Other factors include preexisting developmental orthopedic disease poor conformation; improper hoof balance or shoeing; failure to adequately condition performance horses; monotonous repetitive stresses on bones, tendons, ligaments, and joints in performance horses; hard, slippery, or rocky surfaces upon which horses work; and extremely athletic activities. Inciting factors in lameness include direct or indirect trauma, fatigue resulting in incoordination of muscles (which often occurs in racehorses at the end of races), inflammation, infection, and failure to recognize early disease before it creates significant pain. Lameness in one part of a limb often results in secondary soreness in another area of the same limb and may result in lameness of the contralateral forelimb or hindlimb from overuse due to compensation. The entire horse should be evaluated for secondary lameness even when the cause of the primary problem is obvious. Secondary lamenesses are very common in performance horses but may occur in all types of horses. A dramatic example of a secondary lameness occurs when biomechanical laminitis develops in the normal contralateral limb of a horse with a severe orthopedic problem due to a shifting of weight from the injured limb to the normal limb. Physical examination of Lameness A systematic investigation of a lame horse may be time consuming when the cause is not obvious. The examination benefits from standardized facilities such as a level, firm, nonslip surface for walking and trotting the horse and a soft support area for lungeing and riding the lame horse. The examiner must be knowledgeable in equine anatomy, normal conformation and gaits, regional anesthesia and imaging techniques and be able to recognize forelimb and hindlimb lameness. Conformation should be evaluated and the horse visually checked for symmetry, swellings, muscle loss, abnormal stance, and obvious injuries. The trunk and limbs should be palpated for heat, pain, swellings, and joint effusion. The high degree of variation between horses should be remembered, and comparison with the contralateral limb should always take place, although the latter may not necessarily be a useful control. The reaction of the horse to palpation and the range of flexion and extension of all joints should be noted. The feet should be thoroughly examined, including compression of the walls and sole with hoof testers. Examination during exercise is often required to localize the lameness to a specific limb or site and to evaluate the response to diagnostic regional anesthesia. If lameness is major and acute and a fracture is suspected, exercise should not be undertaken or a catastrophic breakdown may result. Similarly, diagnostic regional anesthesia should not be performed when a fracture is suspected. It is important to determine whether the horse may have been given analgesic medication prior to the lameness examination. The most consistent sign of a unilateral forelimb lameness is the head nod. The head and neck of the horse rise when the lame forelimb strikes the ground and is weightbearing and fall when the sound limb strikes the ground. The sacral rise or pelvic rise is the most consistent and easily observed sign of hindlimb lameness. The entire pelvis and sacrum rise when the lame limb
  2. 2. strikes the ground and is weight bearing and fall when the sound limb strikes the ground. Both head nod and sacral rise serve to reduce concussion on the lame limb. The horse should initially be examined by walking and jogging in hand with a loose line to the halter so that the movement of the horse is not restricted. A firm, nonslippery surface is ideal for trotting on a straight line and for lungeing on a firm surface. It also provides an opportunity to listen to the footfall and consider this information along with the visual appraisal. However, feet of different sizes and shapes and different shoes make slightly different impact sounds, often rendering these sounds of little diagnostic value. Frequently, lameness is more pronounced when the horse is worked in a circle. Circling can be done on a lunge line or in a large round pen or in hand. Lungeing on asphalt or concrete predisposes the horse to slipping and injury but may be done in selected cases to accentuate a very subtle hoof or lower limb lameness. Both forelimb and hindlimb lameness may become worse when the horse is circled; most of the time, the lameness is accentuated when the affected limb is on the inside of the circle. Flexion tests are useful diagnostic tools. The range of movement and response to passive flexion, along with any suggestion of increased lameness or onset of lameness following flexion, should be observed. The distal phalanges in both forelimbs and hindlimbs should be flexed independently of carpus and hock to obtain maximal information. Bending pressure should be firm but not excessive, which can create false positive responses. All tests should be done on both sound and lame limbs for comparison. Consistency should always be applied and individual experience used. A single positive flexion test without associated lameness may not be of significance. To establish consistency, the entire examination should involve the same handler, the same biting when the horse is under saddle, and the same surfaces under foot. The horse should be controlled so that it is trotting at a useful, repeatable pace to evaluate the lameness. Very slight sedation of nervous or fractious horses with 3 mg romifidine or 100 mg xylazine may result in a horse with a more relaxed outline and allow a better assessment without seemingly influencing the degree of lameness. Slowing down the pace at the trot often illustrates a subtle lameness better because the horse loses its momentum and struggles with suspension in the affected limb(s). A ridden assessment of the horse may be necessary, particularly with a subtle lameness that can only be observed under saddle. A multi-limb lameness without an obvious single-limb lameness may also be detected. The clinical signs may be minor (eg, the horse refusing certain movements or activities, slight head tilts, or tail swishing). However, a good rider can, often inadvertently, hide a problem by his or her inherent expertise and ability to ―correct‖ difficulties. Occasionally a horse appears to be sound when lunged and ridden, but the rider feels that the performance is impaired. In such cases it may be worth working the horse on concomitant analgesic or anti-inflammatory medication at therapeutic levels for an adequate period to assess whether improvement occurs. Some clinical signs purported to be caused by lameness are training problems. If improvement on medication occurs, the medication should be withdrawn and diagnostic anesthesia used beginning in an arbitrary limb, most often a forelimb. In this way, multiple limb lamenesses, often mimicking the clinical picture associated with back pain, can be evaluated and treated. Diagnostic regional anesthesia should be used to localize pain in all lame horses in which the lameness can be localized to a specific limb but not to a specific site on the limb. A consistently observable lameness must be present for the clinician to evaluate response to anesthesia. Because lameness may be caused by neuromuscular disorders, a complete neurologic examination should be part of the lameness examination whenever an obvious painful or mechanical cause has not been found. The examination should include evaluation of cranial nerve and upper and lower motor neuron function. Observing the horse execute movements such as turning short, backing, ―hopping‖ on one forelimb (with the other forelimb held up), negotiating a curb, turning in tight circles, and walking up- and downhill should be done. These tests help determine whether reduced proprioception, weakness, or spasticity may be the cause of the gait abnormality.
  3. 3. Imaging Techniques in Equine Lameness IMAGING The visual representation of an object, such as a body part or celestial body, for the purpose of medical diagnosis or data collection using any of a variety of usually computerized techniques [freedictionary.com]. Imaging techniques provide important pathologic and physiologic information necessary to treat specific conditions. Imaging can be divided into anatomic and physiologic methods. Anatomic imaging methods include radiology, ultrasonography, CT, and MRI. Physiologic imaging methods include scintigraphy and thermography. When diagnostic analgesia has failed to eliminate the lameness, the lameness is too subtle for localization by diagnostic analgesia, or the horse is not amenable to handling or injection, physiologic imaging techniques may help narrow the problem to a specific region. Anatomic imaging methods can then be used to evaluate those areas. Imaging may also help prevent injury through early detection of the physiologic changes associated with injury. ANATOMIC IMAGING TECHNIQUES RADIOLOGY Radiologic techniques are the methods most commonly used to evaluate lameness in horses. Plain film radiography requires multiple projections to evaluate any area. It allows assessment of bony tissues and reflects chronic changes. Occasionally, radiographic techniques that provide more information are needed. Contrast radiography provides information about articular cartilage and surfaces and is of particular value in determining whether subchondral cysts communicate with the joint and in delineating subcutaneous tracts. Pathologic diagnoses are usually made by radiography in conjunction with clinical examination. The future of radiography lies in digital techniques such as computed radiography (CR) and digital radiography (DR). CR uses a special plate that is read by the computer. Advantages of CR include fewer retakes, a lower radiation requirement, and postprocessing techniques that eliminate contrast problems. DR also uses a special plate, but the computer reads the radiation directly from the cassette to produce the image. It has the same advantages as CR but is faster. Regardless of the system used, the goal of radiology is to examine the region sufficiently to fully evaluate the anatomic structure. Diagnostic films require preparation, positioning, and production. Preparation involves readying the object to be radiographed. In most cases, this requires the object to be clean and all foreign materials removed (eg, any iodine-based products on the limb will cause artifacts on the radiograph). For radiographs of the hoof, the shoe may need to be removed and the sulci packed in addition to cleaning. Positioning is critical; the object must be evaluated from a sufficient number of angles to insure adequate evaluation. Minimally, this means 2 radiographs 90° apart. Many of the limbs require more views for adequate evaluation. Examination of those projections may necessitate further views to better assess any areas of interest. For instance, the equine foot, fetlock, and carpus require 5 projections, while the pastern and hock require 4. The upper limbs of the horse require fewer projections. This is not because these are less complex areas; rather, the size of the patient makes it difficult to get more projections. Two views can usually be made of the elbow and the stifle. For the shoulder joint usually only 1 view is possible. For the hip, anesthesia is usually required. However, digital radiography has made it possible to take standing hip projections on young horses and those with smaller muscle mass. The production of good radiographs requires the correct exposure of the film. For ambulatory equine practitioners, another factor that must be considered is the electricity output in the barn where the images are taken.
  4. 4. ULTRASONOGRPAHY Ultrasonographic examination can be used to assess any soft tissues. Like radiography, the area to be examined should be evaluated in 2 planes 90° apart. Selection of a probe should take into account the depth, contour, and location of the tissue to be examined. The deeper the tissue to be evaluated, the lower the wavelength of the probe used. The higher the wavelength, the greater the detail that can be achieved. For examination of superficial and deep flexor tendons or the suspensory ligament, a 7.5–10 MHz linear probe is best. Examination of complex anatomic areas such as the distal limb or pelvic region requires a convex linear probe. Examination of the pelvic region internally requires a rectal linear probe. Ultrasonography is most useful in the evaluation of tendons and ligaments but can also be used to evaluate muscle and cartilage. In all cases, tissue fiber alignment and echogenicity are the factors used to determine anatomic disruption. Generally speaking, loss of fiber alignment and decreased echogenicity are signs of acute injury; increased echogenicity is generally thought to indicate chronic conditions. However, if any questions arise during the examination, the opposite limb or area can be examined to compare changes. For the novice ultrasonographer, it is a good idea to compare the right and left sides before making an ultrasonographic diagnosis. Assessment of anatomic changes serves as the basis for any pathologic diagnosis, as well as being important in determining prognosis. For these purposes, radiography and ultrasonography are complementary. Radiography provides information regarding bony tissues, while ultrasonography provides information about the soft tissues that connect bone or provide support. MRI MRI [Magnetic Resonance Imaging] and CT [Computed Tomography] are high-detail anatomic imaging tools. Their use is becoming more common in equine lameness evaluations. MRI in particular has become quite popular. There are 2 types of MRI available: low-field and high-field magnets. High-field scanners produce a stronger signal and higher resolution pictures in a shorter time than low-field scanners. However, some low-field scanners can be used to examine the standing, sedated horse, whereas high-field scanners require the horse to be anesthetized. The standing units can only be used to evaluate from the carpus and hock distally. MRI provides sliced images of the anatomic region of interest. The slices are usually in 3 different planes: axial (transverse), sagittal (longitudinal), and dorsal. MRI of orthopedic disease is performed in several acquisition sequences. Each sequence displays different anatomic, physiologic, and pathologic information. The most common sequences are the proton density and the T1- weighted and T2-weighted images. Proton density provides the most anatomic detail. Tl- weighted images highlight the structural characteristics of bone and soft tissues, while T2- weighted images emphasize the fluid characteristics of tissues and are sensitive for detecting synovial effusions, cysts, and edema. Special sequences can further clarify or highlight a lesion. For instance, fat-suppressed sequences are used to evaluate edema in high-fat signal areas such as the bone marrow. CT Commonly referred to as CT scans, computed tomography is a technology that uses very small x-ray beams from many different angles around the body (called a slice) that are reconstructed by computer to produce an image. Because the images are in slices, there is less interference from surrounding anatomy. Therefore, the CT scanner provides the clearest images possible of the limbs, joints, nasal passages, skull, sinus cavities, and neck. These images improve the clinician's ability to accurately define and identify the extent of abnormalities of these regions. PHYSIOLOGIC IMAGING TECHNIQUES These techniques provide images that reflect physiologic processes. Unlike anatomic imaging, which reflects structure, physiologic imaging techniques assess metabolism or circulation. Thermography and scintigraphy allow examination of the entire horse. When combined with a
  5. 5. thorough clinical examination, these methods are useful for identifying injuries that may otherwise go undetected. Thermography is the pictorial representation of the surface temperature of an object. It is a noninvasive technique that measures emitted heat and is useful for detecting inflammatory changes that may contribute to lameness. Relative blood flow dictates the thermal pattern; normal thermal patterns can be predicted based on vascularity and surface contour. Skin overlying muscle is also subject to temperature increase during muscle activity. Circulation is invariably altered in injured or diseased tissues. Thermographically, the ―hot spot‖ associated with the localized inflammation generally is seen in the skin directly overlying the injury. However, diseased tissues may have a reduced blood supply due to swelling, vessel thrombosis, or tissue infarction. With such lesions, the area of decreased heat is usually surrounded by increased thermal emissions, probably due to shunting of blood. During scintigraphy, polyphosphonate radiopharmaceuticals are given IV. Their distribution is then measured by a gamma camera. The polyphosphonates bind rapidly to exposed hydroxyapatite crystal, generally in areas where bone is actively remodelling. Because inflammation causes an increase in blood flow, capillary permeability, and extracellular fluid volume, inflamed tissues accumulate high levels of radio-pharmaceutical during the soft-tissue phase of scintigraphy, allowing evaluation of soft-tissue injuries. During the bone phase, the radiopharmaceutical accumulates in areas of increased remodelling or vascularity. Because injured bone is remodelled more rapidly, scintigraphy is useful for detecting lesions in bone and ligaments, particularly in identifying enthesopathy (damage to the insertions of tendons and ligaments on bone). Regional Anesthesia in Equine Lameness Regional anesthesia is a valuable diagnostic aid used to localize lameness when, after a thorough clinical examination, the site of pain remains uncertain. Localizing pain allows other diagnostic procedures, such as anesthesia of a joint, radiography, ultrasonography, CT, scintigraphy, or MRI to be used more effectively and economically to identify the cause of lameness. Additionally, use of regional anesthesia allows some surgical procedures to be performed without the need for general anesthesia, and it can be used to provide temporary, humane relief of pain. Lidocaine HCl (2%) and mepivacaine HCl (2%) are the local anesthetic agents most commonly used to induce regional anesthesia during the lameness examination. Mepivacaine HCl is preferred by most clinicians because it causes less tissue reaction than lidocaine HCl. Bupivacaine HCl is used to induce regional anesthesia for humane relief of pain because it provides anesthesia that lasts 4–6 hr. The choice of anesthetic agent may depend on its duration of action. The anesthetic effect of mepivacaine HCl, which lasts 90–120 min, makes this agent valuable for examining a horse with lameness in multiple limbs or if multiple sites of pain on a limb are suspected. Lidocaine HC1, which has an anesthetic effect of only 30–45 min, might be the preferred local anesthetic agent when different techniques of diagnostic analgesia are likely to be used during the lameness examination. Before performing regional anesthesia, the horse should be consistently and sufficiently lame so that any improvement in gait can be detected. Lungeing or riding the horse may exacerbate a subtle lameness. The lameness of some horses improves or resolves during exercise; for these horses, a false-positive response to regional anesthesia may result if the horse has not been sufficiently exercised before it is examined. If a horse is subtly lame, independent observation and grading of its gait before and after regional anesthesia by 2 or more clinicians skilled at lameness examination may increase the accuracy of interpretation. Complications of regional nerve blocks are rare, but include a broken needle shaft, SC infection, and infection of a synovial structure adjacent to the nerve that was anesthetized. Local
  6. 6. anesthetic solution is detectable systemically, which could create a problem for a horse participating in a competition if the horse's serum is examined for the presence of drugs. REGIONAL ANESTHESIA OF THE FORELIMB Because perineural analgesia should start distally and progress proximally, the palmar digital nerve (PDN) block is probably the most commonly performed regional nerve block of the forelimb. The PDN block is performed with the limb held. The needle is inserted directly over the palpable neurovascular bundle ~1 cm above the cartilage of the foot. The needle is directed distally, and 1.5 mL of local anesthetic solution is deposited near the junction of the nerve and the cartilage of the foot. The PDN block is sometimes called a ―heel block,‖ but this terminology is erroneous because the block anesthetizes the entire foot, including the distal interphalangeal (coffin) joint. For a few horses, the PDN block may also cause at least partial anesthesia of the proximal interphalangeal (pastern) joint, especially if a large volume of local anesthetic solution is injected. If the horse's gait fails to improve after a PDN block, some clinicians next administer a semi- ring block at the pastern to anesthetize the dorsal branches of the digital nerve that supply the foot. Because the dorsal branches of the digital nerve contribute little to sensation within the foot, a semiring block at the pastern is unlikely to improve the gait if a PDN block failed to improve the gait, however. Most clinicians proceed to an abaxial sesamoid nerve block if the horse's lameness is not reduced with a PDN block. With this regional nerve block, the palmar nerves are anesthetized at the level of the proximal sesamoid bones, before the nerve branches into the dorsal and palmar digital nerves. When performing an abaxial sesamoid nerve block, 2.5–3 mL of local anesthetic solution is deposited at the base of the proximal sesamoid bones over the neurovascular bundle, which is easily palpated at this location. More proximal deposition of local anesthetic solution may anesthetize a portion of the fetlock joint. Positive response to an abaxial sesamoid nerve block, performed after a PDN block has failed to ameliorate lameness, localizes the site of pain causing lameness to the pastern. The low palmar nerve block, or low 4-point block, is performed after a negative response to the abaxial sesamoid nerve block. This nerve block is usually performed with the horse bearing weight on the limb, but it can also be performed with the limb held. The medial and lateral palmar nerves are anesthetized, using a 25-gauge, 5/8-in. needle, by depositing 2 mL of local anesthetic solution over each palmar nerve where it lies subcutaneously at the dorsal border of the deep digital flexor tendon. To complete the block, 1–2 mL of local anesthetic solution is deposited SC at the distal end of each splint bone, where the palmar metacarpal nerve lies next to the periosteum of the third metacarpal bone. A positive response to a low 4-point block, performed after a negative response to an abaxial sesamoid nerve block, localizes the site of pain causing lameness to the fetlock, or that portion of the superficial or deep flexor tendon or suspensory ligament distal to the block. The high palmar nerve block, or high 4-point block, can be performed when the low 4-point block fails to improve lameness. With the limb bearing weight, the medial and lateral palmar and palmar metacarpal nerves are anesthetized slightly distal to the level of the carpometacarpal joint. To anesthetize a palmar nerve, a 25-gauge, 5/8-in. needle is inserted through fascia to where the nerve lies near the dorsal border of the deep digital flexor tendon, and 3–5 mL of anesthetic solution is deposited over the nerve. Anesthetizing the medial and lateral palmar nerves alone desensitizes the flexor tendons and inferior check ligament. With the limb held or bearing weight, the palmar metacarpal nerves are anesthetized slightly distal to the level of the carpometacarpal joint by inserting a 20- to 22- gauge, 1 ½;-in. needle into the angle formed by the junction of the third metacarpal bone and the second or fourth metacarpal bone. Anesthetizing the medial and lateral palmar metacarpal nerves alone desensitizes the splint bones and their interosseous ligaments and the proximal aspect of the suspensory ligament.
  7. 7. An easier alternative to the high palmar nerve block, when the site of pain causing lameness is suspected to be in the proximal portion of suspensory ligament, is the lateral palmar nerve block, which is performed, with the limb bearing weight, by inserting a 25-gauge, 5/8-in. needle over the lateral palmar nerve where it courses over the medial aspect of the accessory carpal bone. The needle is inserted in a medial to lateral direction at the distal third of a palpable groove, and 2 mL of local anesthetic solution is deposited. Because the medial and lateral palmar metacarpal nerves arise from the lateral palmar nerve distal to this site, the structures they innervate, such as the proximal aspect of the suspensory ligament, are desensitized. If the site of pain causing lameness cannot be localized by performing the previously discussed nerve blocks, most clinicians perform joint blocks of the carpus, elbow, or shoulder. The order in which these synovial structures are desensitized is not important. The median, ulnar, and medial cutaneous antebrachial nerves are sometimes anesthetized as part of a lameness evaluation, but more commonly, they are anesthetized to allow surgery of the limb without the need for general anesthesia. REGIONAL ANESTHESIA OF THE PELVIC LIMB Techniques for administering regional anesthesia of the distal portion of the pelvic limb are slightly different than the techniques for administering regional anesthesia of the forelimb, because branches of the deep peroneal (fibular) nerve of the pelvic limb supply additional innervation to this region. These branches, the medial and lateral dorsal metatarsal nerves, course adjacent to the extensor tendon and innervate the dorsal aspect of the laminar corium. After depositing local anesthetic solution for a low 4-point nerve block at the level of the distal aspect of the splint bones, the needle is redirected dorsolaterally or dorsomedially, parallel to the bearing surface of the foot, and an additional 2 mL of local anesthetic solution is deposited SC to anesthetize the medial or lateral dorsal metatarsal nerves. Most lamenesses of the pelvic limb can be evaluated accurately without anesthetizing the dorsal metatarsal nerves, however. The high plantar nerve block is administered, using techniques similar to those used to administer the high palmar nerve block, ~1 cm distal to the tarsometatarsal joint. When the proximal aspect of the suspensory ligament is suspected to be the site of pain causing lameness, 3–4 mL of local anesthetic solution can be deposited through a 20- to 22-gauge, 1 ½- in. needle, axial to the lateral splint bone and ~l cm distal to the tarsometatarsal joint, between the tendon of the deep digital flexor muscle and the suspensory ligament. The solution diffuses to anesthetize the deep branch of the lateral plantar nerve, which branches into the medial and lateral plantar metatarsal nerves that supply the proximal aspect of the suspensory ligament. Osseous Cyst-Like Lesions in the Distal Phalanx in Horses A large cyst in the distal phalanx can result in a lameness that varies from mild to severe and may be unresponsive to anti-inflammatory medication. There is no apparent age, breed, or sex predisposition. Cysts are assumed to be traumatic in origin and not part of the osteochondrosis syndrome. They are most commonly located in the subchondral bone either in the extensor process or along the joint surface close to the midline; the cysts may communicate with the distal interphalangeal joint. The lameness usually responds to intra-articular anesthesia of the distal interphalangeal joint, and may respond to palmar digital nerve anesthesia. Diagnosis is confirmed by radiography and/or CT. Differential diagnoses include keratoma, navicular disease, and primary degenerative joint disease of the distal interphalangeal joint. Surgical treatment includes arthroscopic debridement or arthroscope-assisted corticosteroid injection into accessible cyst-like lesions; extracapsular (through the hoof wall) approaches have been used in less accessible lesions. Secondary fracture of the distal phalanx (especially the extensor process) can occur due to progressive weakening of the bone. Some horses return to performance status, while others are salvaged for alternative uses such as breeding. Bruised Sole and Corns in Horses Bruising on the solar surface of the foot usually is caused by direct injury from stones, irregular ground, or a poorly fitting shoe. Whereas subsolar bruising can occur anywhere on the solar surface, bruising in the caudal sole at the buttress is termed a corn. Horses with flat feet or dropped soles are predisposed to bruising, usually at the toe or around the periphery of the sole. The severity of solar bruising can range from some red staining of the inner solar
  8. 8. epidermis to the presence of serum either under the solar epidermis or seeping through it. If left untreated, the affected area can become infected Persistent, nonresponsive bruised sole dorsal to the apex of the frog suggests possible displacement of the distal phalanx secondary to laminitis. A ―corn‖ is most common in the forefeet on the inner buttress and can be caused by: 1) the heel of a shoe that is improperly placed, 2) a shoe that is left on too long, causing pressure on the buttress, and 3) shoes that have been fitted too closely at the quarters or are too small for the foot. Corns are described as dry moist or suppurative. Bruising may be associated with lameness, depending on the severity. When the foot is raised and the solar surface freed of dirt and loose horn, a discoloration, either red or reddish yellow, is noted. Pressure on the affected area with hoof testers usually causes varying degrees of discomfort, again depending on the severity of the lesion. Treatment is intended to remove pressure and protect the bruised area. In horses predisposed to corns, proper shoeing with branches that fit well on the hoof wall at the quarters and heels will decrease the incidence of lesions. In animals predisposed to bruising due to dropped soles, application of a wide-webbed shoe that is beveled on the solar surface to avoid solar pressure will help protect the sole. Additionally, a pad can be placed on the foot to protect the sole. This type of shoeing will generally help animals with sole bruising also. In animals with painful corns, the affected heel can be unweighted by trimming the wall and insensitive sole to minimize contact with the shoe until healed; a bar shoe can also help disperse pressure away from the trimmed area. If the bruise/corn is suppurating, ventral solar drainage, usually established with a hoof knife, is usually adequate to allow healing. If the affected subsolar area is large, the abscess can usually be addressed by establishing small areas of drainage at opposite sides of the affected area followed by lavage with saturated Epsom salt solution via either a 14-gauge catheter or teat cannula attached to a 60-mL syringe, repeated daily or every other day until healed. This is usually more effective than foot baths or application of poultices. The sole should be covered until the solar surface is covered by tough epithelium. Parenteral antibacterial therapy is of questionable value unless cellulitis is present proximal to the coronary band. Canker Canker is a chronic hypertrophy and apparent suppuration of the horn-producing tissues of the foot, involving the frog and the sole. The cause is unknown. Although frequently described as a disease seen in animals kept in moist or unsanitary environments, it is also encountered in well- cared-for animals. The disease can be observed in both front- and hindfeet. The disease most commonly starts in the caudal frog, where the affected area consists of an inflamed granulation tissue with proliferative epithelium, often appearing as fronds. The affected tissue is commonly covered by caseous exudate, which may be foul smelling. The surface of the lesion is irregular with a characteristic, cauliflower-like vegetative growth. The disease process may extend to the sole and even to the wall, showing no tendency to heal. Treatment requires radical debridement down to normal corium, using either sharp debridement or electrocautery. All loose horn and affected tissue should be removed. If sharp debridement is used, cryotherapy can be applied subsequently to kill affected tissue not removed by sharp debridement. Following debridement, an antiseptic or antibiotic dressing should be applied daily; good results have been reported using a solution of benzoyl peroxide dissolved in acetone. Metronidazole is commonly applied topically. A clean, dry wound environment must be maintained to allow healing, which may take weeks or months. Waterproof materials and plastic boots are used for such purposes. Navicular bone fractures Navicular bone fractures are usually a result of trauma or excessive concussion to the foot, but the cause is not always known. It is much less common than distal phalanx fracture and is more commonly observed in the forelimb. Although pain is variable, hoof testers usually induce a painful response over the frog. Lameness is severe with acute fractures, but it may be less in a chronic fracture in which a fibrous union has presumably failed. The lameness usually is markedly improved by palmar digital nerve block. Radiography confirms the diagnosis, in which a sagittal fracture is usually found medial or lateral to the midline; care must be taken to pack the sulci of the frog to avoid artifacts that appear as navicular bone fractures.
  9. 9. Conservative treatment is prolonged rest with corrective shoeing to apply a dramatically raised heel but a satisfactory bony union at the fracture site seldom occurs. The prognosis is guarded to poor. Surgical repair by lag screw has been described to have a better prognosis. Fracture of the distal phalanx is a fairly common injury that usually occurs at moderate or high speed. It occurs due to concussion and produces a sudden onset of lameness. The lameness is severe if the fracture is intra-articular, but may be less severe if only a wing is fractured with no articular component. Distal phalangeal fractures occur more frequently in the forelimb but are also common in the hindlimb. Intra-articular fractures may be easily isolated to the foot; lameness is usually associated with joint effusion. Nonarticular fractures may require compression of the foot with hoof testers and possibly unilateral palmar digital nerve anesthesia for localization. Lameness is exacerbated by turning the horse or making it pivot on the affected leg. If the fracture does not extend into the joint, the lameness may improve considerably after 48 hr of stall rest. The clinical signs may be suggestive, but the diagnosis is confirmed by palmar digital nerve block and radiography. Often, more than 2 views are required before the fracture line is evident. Radiographic confirmation may be difficult immediately after the injury because the fracture is only a hairline at this stage. Repeating the radiography several days or weeks later and using oblique views may be necessary to confirm the presence and exact site of the fracture. Additionally, if the suspected fracture is in a wing of the distal phalanx, unilateral palmar digital nerve anesthesia may be performed to localize the lameness to that side. Determining whether the fracture extends into the distal phalangeal joint is important. Conservative treatment of 6–9 mo rest is usually all that is required for fractures that do not involve the joint. Fractures often heal with a fibrous union, so that even though the horse returns to soundness, radiographic evidence of the fracture remains. A straight bar shoe with a clip well back on each quarter can be applied to limit expansion and contraction of the heels. In young horses, fractures into the joint may heal satisfactorily, provided a 12-mo rest period is given. Older horses have a much less favorable prognosis, and insertion of a cortical bone screw using interfragmentary compression across the fracture site is indicated. However, infection is a frequent complication, as it requires an extracapsular approach. Many fractures heal in the presence of infection, but the screw must be removed at a second surgery to restore the horse to complete working soundness. Unilateral palmar digital neurectomy of racehorses with wing fractures has been used to allow return to competition without the delay for complete healing. Keratoma in Horses (KERAPHYLLOCELE) A keratoma is a benign mass made up of keratin that is situated between the hoof wall and distal phalanx. The cause is unknown. The condition may be difficult to detect until the growth is well advanced. There may be bulging of either the coronary band or the hoof wall over the keratoma, depending on its position within the foot. Pressure from the keratoma causes bone resorption of the distal phalanx in most cases, which can be visualized via the 65° dorsopalmar radiographic view of the distal phalanx. Surgical removal of the mass is indicated. If possible, it is best to localize the mass using different imaging techniques only resect the hoof wall immediately over the mass. Laminitis in Horses (Founder) Equine laminitis is a crippling disease in which there is a failure of attachment of the epidermal laminae connected to the hoof wall from the dermal laminae attached to the distal phalanx. As the laminae are responsible for suspending the distal phalanx within the hoof wall, laminar failure in combination with the downward forces of the weight of the horse and distracting forces such as the tension from the deep digital flexor tendon commonly results in a catastrophic displacement of the distal phalanx resulting in severe lameness. Laminitis affects all breeds of horses. Etiology and Pathogenesis There are 3 main disease states thought to be associated with laminitis: 1) diseases associated with sepsis or endotoxemia, 2) equine metabolic syndrome and 3) supporting limb laminitis. The pathogenesis of laminitis is still controversial and most likely varies widely between these 3 primary causes. A fourth, less common cause is ingestion of shavings from black walnut heartwood. The most common causes of sepsis or endotoxemia-related laminitis are diseases associated with gram-negative bacteria sepsis and include ingestion of excess carbohydrate,
  10. 10. postparturient metritis, colic, and enterocolitis. Laminitis secondary to equine metabolic syndrome most commonly occurs in overweight horses and ponies, and is commonly exacerbated when grazing lush pastures. Supporting limb laminitis can occur any time the animal places excessive weight on one limb for an extended period of time due to inability to use the other limb. The basic cause of laminar failure in laminitis is a failure of attachment of the laminar basal epithelial cells of the epidermal laminae to the underlying dermal laminae. Although the cause of this failure was thought to be primarily due to breakdown of the matrix molecules in the basement membrane and dermis by matrix metalloproteases, it now appears that the LBEC may also be losing attachment due to dysregulation of the hemidesmosomes, the adhesion molecules on the LBEC that attach the cells to the underlying matrix molecules. Marked increases of inflammatory mediators and enzymes occur in the laminae in the early stages of laminitis and may injure the LBEC. Hypoxia and ischemia due to aberrant vascular flow is also likely to play a role in LBEC dysfunction. The pathophysiology behind laminitis associated with equine metabolic syndrome is not as well researched but is proposed to occur due to a similar inflammatory state as that associated with insulin resistance in obese humans with metabolic syndrome and that leads to vascular injury. The pathogenesis of supporting limb laminitis is not known. Following loss of integrity of the laminar attachments, the distal phalanx can undergo 3 types of displacement depending on the forces placed on the foot and the pattern of laminar injury. Distal displacement of the entire phalanx occurs when there is circumferential loss of laminar attachments, most commonly observed in severe cases of sepsis or endotoxemia but also observed in equine metabolic syndrome. Palmar rotation of the distal margin of the distal phalanx is the most common displacement observed, and most likely occurs due to primary loss of the dorsal laminar attachments with some integrity maintaining in the quarters. Rarely, unilateral distal displacement of the distal phalanx occurs, most commonly to the medial side; this displacement can only be visualized on an anterior-posterior radiograph of the foot. In laminitis related to sepsis and equine metabolic syndrome, the forelimbs are most commonly affected, although the hindlimbs can also be affected in severe cases. In supporting limb laminitis, either a front or rear foot is affected depending on which opposite limb has the weight- bearing problem. Clinical Findings Classically, laminitis is considered acute, subacute, or chronic. Acute cases are of short duration and have not undergone displacement of the distal phalanx. Subacute cases have continued >3 days, but still have no distal phalangeal displacement. Chronic laminitis cases have distal phalanx displacement regardless of the duration of the disease. Early in laminitis, the horse is depressed and anorectic and stands reluctantly. Resistance to any exercise is marked, and the normal stance is altered in attempts to relieve the weight borne by the affected feet. If only the forelimbs are affected, the horse will stand with the forelimbs placed far forward the hindlimbs also are placed more forward in order to support more of the weight. If forced to walk, the horse shows a slow, crouching, short-striding gait. If all 4 limbs are affected, the animal will appear ―camped out‖ with the forelimbs placed more forward than usual, and the hindlimbs placed more caudally than usual. Each foot, once lifted, is set down as quickly as possible. The entire hoof wall may be warm in the acute stage. An exaggerated and bounding pulse can be palpated and may be visible in the digital arteries. Pain can cause muscular trembling, and a fairly uniform tenderness can be detected when pressure is applied to the feet. There is commonly an increased pulse rate (60–120/min) and respiratory rate (80–100/min). In exceptionally severe cases, for which the prognosis is unfavorable, a blood-stained exudate may seep from the coronary bands. Radiographic evidence of displacement of the distal phalanx can be present as early as the third day after the onset of disease in horses with sepsis or endotoxemia. However, a recent MRI study has shown that, in the acute case, the animal may have normal-appearing distal phalanx radiographs, despite destruction of the entire dorsal laminar attachment that is visible on MRI. Subacute cases, commonly observed in horses with equine metabolic syndrome, may exhibit any or all of the above clinical signs but to a lesser degree. Often, there is only a mild change in stance, with reluctance to walk and some increased sensitivity to concussion on the soles of the affected feet. There may be no demonstrable heat in the coronary band or increase in digital
  11. 11. pulse. The acute and subacute forms of laminitis tend to recur at varying intervals and may develop into the chronic form. During and immediately following displacement of the distal phalanx, the horse is usually extremely lame and may spend a great deal of time recumbent. In severe cases, the foot may prolapse through the sole cranial to the frog, or the coronary band may separate; both occurrences gravely affect the prognosis. Longterm cases of chronic laminitis are characterized by changes in the shape of the hoof and usually follow one or more attacks of the acute form. Bands of irregular horn growth (laminitic rings) may be seen in the hoof, close at the toe and diverging at the heel. The hoof itself becomes narrow and elongated, with the wall almost vertical at the heel and horizontal at the toe. As the condition progresses, the sole becomes thickened and either flattened or somewhat convex in outline. The gait is similar to that already described, and when standing, the body weight is continually shifted from one foot to the other. Radiography reveals rotation and some osteoporosis of the distal phalanx. The corona of the bone is forced downward and presses on the horny sole. In severe cases, it may penetrate the sole just in front of the point of the frog. Diagnosis In acute and severe laminitis, diagnosis is usually straightforward and is based on the history and posture of the horse, increased temperature of the hooves, a hard pulse in the digital arteries, and reluctance to move. Abaxial sesamoid nerve blocks of the forelimb digits in the very lame horse allow assessment of possible involvement of the hind feet (by walking the animal a few steps) and enable full assessment of the soles of both feet. These nerve blocks also make it possible to obtain good quality lateral and anterior-posterior radiographs of the foot. Lidocaine should be used for the nerve block as it will only last a short time, ie, not long enough for the animal to move excessively and further damage the laminae. Gross observation and distinct measurements from the radiographs allow determination of whether distal displacement, rotation, both distal displacement and rotation, or unilateral sinking has occurred. Treatment Acute laminitis constitutes a medical emergency because phalangeal displacement can occur rapidly. Despite prompt therapy, the prognosis is guarded until recovery is complete and it is evident that the hoof architecture is not altered. Most animals should be administered NSAID, with flunixin meglumine being the drug of choice if the horse is still systemically ill. Phenylbutazone is usually used in the early chronic stage when the horse is lame but does not have signs of systemic disease. Close attention to the potential toxicities of NSAID therapy, particularly with phenylbutazone, is required. Because phenylbutazone accumulates in the tissue, it is best to skip a day every 5–7 days to ―clear the system‖. NSAID should be used according to label instructions and, if used in the early chronic stage when the horse is lame but does not have signs of systemic disease. Close attention to the potential toxicities of NSAID therapy, particularly with phenylbutazone, is required. Another recent option for treatment of chronic laminitis is the COX-2-selective NSAID. During the first 2–3 wk, it is important to remove standard shoes, as shoes place the majority of stress on the hoof wall and therefore the laminae. The feet should be padded with a soft, resilient substance such as a 1- to 2-in. thick piece of closed-cell foam cut to the diameter of the foot. Pads can also be made from the different putties available to the farrier to provide sole support. Decreasing padding in the region dorsal to the apex of the frog decreases the stress on the dorsal laminae. Styrofoam insulation can be used in small equids but usually provides minimal support in larger animals. Other shoes that can be applied without severe concussion are available for application to the foot in the first few weeks. Shoeing horses with laminitis is usually not a good option until ~3 wk after the onset of laminitis, when the laminar structure may be stabilizing. The type of shoeing depends on the type of displacement. In a horse with distal phalangeal rotation, an attempt is made to begin realigning the palmar surface of the distal phalanx to the sole, while not allowing excessive forces on the laminae. The breakover of the shoe is moved as far caudally as possible, and some of the caudal hoof is removed to allow realignment to the sole. This may have to be performed in combination with raising of the heel, which still allows alignment of the distal phalanx to the solar surface while avoiding excessive changes in relation to the ground surface, thus preventing excessive tension on the deep digital flexor tendon and the dorsal laminae. It is usually appropriate to place some type of resilient putty on the solar surface to provide support to the distal phalanx. Multiple types of shoes can be used, including heart bar shoes, egg bar shoes, and natural balance shoes. Steward clogs are an option for treating horses with distal
  12. 12. displacement of the distal phalanx; these allow the animal to maximize comfort in multiple directions. Surgical options include deep digital flexor tenotomy, to neutralize the pull of the deep digital flexor tendon, and dorsal hoof wall resections. Deep digital flexor tenotomy is most commonly performed in cases of chronic rotation that do not respond to the above shoeing techniques; it should always be accompanied by aggressive derotation via rasping of the caudal foot. The farrier and veterinarian must address subluxation of the coffin joint subsequent to surgery in the majority of cases. Generally, only a partial hoof wall resection is performed due to the severe digital instability caused by removing the entire dorsal wall. Navicular Disease in Horses (Palmar foot pain, Podotrochlosis, Podotrochlitis) Navicular disease is one of the most common causes of chronic forelimb lameness in the athletic horse but is essentially unknown in ponies and donkeys. Navicular disease is a chronic degenerative condition of the navicular bone that involves: 1) loss of the medullary architecture 2) bone sclerosis combined with damage to the fibrocartilage on the flexor surface of the bone, 3) traumatic fibrillation of deep digital flexor tendon from contact with the damaged flexor surface of the bone with adhesion formation between the tendon and bone, and 4) enthesiophyte formation on the proximal and distal borders of the bone. Etiology The syndrome is likely due to a complex pathogenesis rather than a specific disease entity, although the greatest consensus appears to be that there is a biomechanical component and possibly a vascular component. There appears to be a hereditary predisposition, indicated by the sharp decrease in incidence of the disease in Dutch Warmbloods following the disallowance of stallions with severe navicular changes to be certified for breeding. It is considered to be a disease of the more mature riding horse, commonly not appearing until 8–10 yr of age. Conformation of the distal limb is likely to play a large role in the disease process and degree of lameness. Excessive pressure on the navicular bone occurs with a ―broken back‖ hoof-pastern axis, usually accompanied by an underrun heel and excessively long toe. This conformation, leading to excessive concussion between the flexor tendon and the navicular bone, may also cause navicular bursitis, with direct damage to the fibrocartilage of the flexor surface and the collagenous surface of the flexor tendon itself. Clinical Findings and Diagnosis The disease is usually insidious in onset. An intermittent lameness is manifest early in the course of the disease. Because disease is bilateral, there may be no obvious head nod to the lameness when the horse is trotted in a straight line, with only a shortened stride present. Lameness is usually exacerbated by lungeing the horse in a circle, with the inside foot usually exhibiting the greatest lameness. In early stages of the disease, the lameness may not be visible even at a lunge until a nerve block is performed on 1 of the 2 digits. A flexion test of the distal forelimb may produce a transient exacerbation of lameness. Clinical diagnosis is mainly based on the presentation of the animal, and, importantly, on the lameness examination including a characteristic response to palmar digital nerve anesthesia. The horses are rarely positive to hoof testers. The lameness can be eliminated by palmar digital nerve block. However, as this nerve block anesthetizes the entire sole and coffin joint in addition to the heel, response to the block itself is not diagnostic. A transfer of lameness to the other forelimb, which also is eliminated by a palmar digital nerve block, is necessary for a tentative diagnosis of navicular disease. Anesthesia of the navicular bursa is much more specific, but is not commonly performed during a lameness examination due to the pain involved and complexity of the injection. Radiographic changes are variable and do not always correlate with the severity of lameness. Thus, they are not as important in the diagnosis as the lameness examination. Radiographs may demonstrate a range of degenerative changes involving the navicular bone: marginal enthesiophytes, enlarged synovial fossae and cysts due to loss of medullary trabecular bone, and flexor surface changes. Treatment Because the condition is both chronic and degenerative, it can be managed in some horses but not cured. The most common effective treatments include NSAID administration and corrective shoeing. Phenylbutazone is the most commonly used NSAID, but must be used with caution due to adverse effects. If used daily, it may be best to take the animal off the drug one day a week to allow the body to clear some of the accumulated drug; the horse can be given flunixin
  13. 13. for that day. A safer option is the COX-2-selective NSAID firocoxib, which is fairly effective for orthopedic and articular pain. With severe lameness, rest is indicated. Foot care should include trimming and shoeing that restores normal phalangeal alignment and balance; response to corrective shoeing commonly takes ~2 wk. The principal object of shoeing is to decrease the pressure on the navicular bone. The shoeing technique that most effectively decreases pressure on the navicular area is raising the heel. Rolling the toe of the shoe further relieves the pressure on the navicular bone. The egg bar shoe does not decrease navicular pressure in sound horses on a hard surface, but has been reported to effectively decrease forces on the navicular bone in some horses with navicular disease or collapsed heels. Additionally, egg bar shoes are likely to more effectively decrease forces on the navicular area on soft surfaces; they work somewhat like a snowshoe and do not allow the heel to sink as deeply as a foot with a standard shoe would. Natural balance shoes are ineffective at decreasing navicular pressure. Injection of the coffin joint with corticosteroids will markedly improve soundness in ~⅓ of horses, whereas injection of corticosteroid into the navicular bursa is reported to resolve the lameness for an average of 4 mo in 80% of horses that do not respond to standard treatments. Increased incidence of rupture of the deep digital flexor tendon has been reported with multiple intrabursal injections. Isoxsuprine hydrochloride is ineffective as a vasodilator when administered orally and has little therapeutic value. Palmar digital neurectomy may provide pain relief and prolong the usefulness of the horse, but no neurectomy should be considered curative. Digital neurectomy has a high incidence of severe complications such as painful neuroma formation and rupture of the deep digital flexor tendon. Other surgical procedures for navicular disease are unproven. Although the prognosis is guarded to poor, a carefully designed therapeutic regimen can prolong the usefulness of most horses, and the competitive status of many. Over months or years, the majority of affected horses reach a point of nonresponsiveness to treatment. Pedal Osteitis in Horses Pedal osteitis is a radiographic finding of demineralization of the solar margin of the distal phalanx, commonly associated with widening of vascular channels near the solar margin, which is best observed on a 65° proximal-distal dorsopalmar radiographic view. Although the term is usually used to describe changes in the dorsal distal solar margin, it can be used to describe bone resorption of any aspect of the solar margin of the distal phalanx. The bony resorption usually occurs due to chronic or repeated pressure and/or inflammation of the affected region. The resorption can be focal due to a focal lesion such as a keratoma, or it can be more diffuse in states such as chronic toe bruising, in which the entire distal margin of the toe may appear ―moth-eaten‖ due to extensive resorption of the solar margin. Resorption in the toe region commonly occurs in chronic laminitis cases in which displacement of the distal phalanx results in inadequate sole depth between the ground surface and solar margin of the distal phalanx, resulting in chronic trauma and inflammation of that region of the phalanx and surrounding soft tissue. Because the bone resorption is usually permanent, the radiographic finding does not indicate current pathology and may be due to a pathologic state that occurred years ago. Therefore, it is essential that a thorough examination be performed, including application of hoof testers to the entire solar margin of the foot and a lameness examination with nerve blocks if lameness exists. Navicular disease is an important differential diagnosis to pedal osteitis-associated toe bruising, because toe bruising is also commonly bilateral and both conditions respond to a palmar digital nerve block. Radiography is helpful in diagnosis and in differentiation from navicular disease. Pedal osteitis associated with chronic subsolar abscess is usually aseptic, with the sepsis isolated to the soft tissue, but lucency can also be an artifact caused by subsolar gas once an abscess is drained. Curettage of the affected distal phalanx should be avoided unless it is documented to be septic. Treatment is necessary only if there is an active process associated with the radiographic changes of pedal osteitis. Treatment should be directed at the primary disease that caused the resorption. Puncture Wounds of the Foot in Horses (Subsolar abscess, septic navicular bursitis)
  14. 14. Puncture wounds are common in horses, and are the most common cause of subsolar sepsis. The majority of puncture wounds result only in sepsis of the subsolar soft tissue, but can be catastrophic when the puncture is in the frog and travels deep enough to enter synovial structures such as the navicular bursa, the distal interphalangeal joint, or the deep digital flexor tendon sheath. Puncture of the sole by a foreign body is associated with introduction of pathogenic microorganisms that lead to subsolar abscess formation. Lameness is usually severe; the degree of lameness may be similar to that of a fracture. The horse may stand pointing the affected foot. There is commonly a prominent digital pulse in the affected limb. If allowed to progress, the abscess may travel proximally to rupture at the coronary band; there will usually be edematous swelling proximal to the coronary band prior to rupture. Diagnosis is made by confirming the site of pain by pulling the shoe, using hoof testers, and picking or paring the suspect area to locate the foreign body or its dark tract. If a foreign body is found in the frog, it may be best to obtain a lateral radiograph of the foot to assess the structures penetrated prior to removing the offending object. If a tract is found in the frog, it should be probed and a radiograph taken with the probe in place. Because puncture wounds in or near the frog commonly enter a synovial structure, they constitute a serious problem requiring rapid, aggressive diagnosis and therapy. If a synovial structure is entered, the horse should be placed on broad-spectrum antibiotics and transported to a facility capable of advanced surgical and medical techniques; the affected synovial structure should be lavaged with sterile polyionic solution as soon as possible . If a puncture wound is noted in the solar area, ensuring adequate drainage from the site helps prevent abscess formation. If there is a suspected abscess but no tract is found, the foot can be poulticed in an attempt to promote organization of the abscess for localization. If a tract is found that leads to a subsolar abscess, adequate drainage should be established with a hoof knife; the drainage hole should be kept as small as possible to avoid a prolapse of sensitive corium. Some farriers and veterinarians prefer to drain the abscess through the hoof wall if possible. The abscess should then be probed to determine its extent; a palmar digital nerve block will usually be necessary prior to probing and lavage of the area. If the abscess underruns a large area of the foot, it can be lavaged by placing a 14-gauge catheter or teat cannula into the affected subsolar space and flushing with saturated Epsom salt solution. If a chronic subsolar abscess has developed, this treatment may have to be repeated. The foot should then be kept in a rubber or plastic boot for several days; a cotton pad soaked in saturated magnesium sulfate solution or other suitable poultice can be applied to the foot for 12 hr/day until all drainage ceases. All horses with puncture wounds should be immunized against tetanus. Local and systemic antibiotic therapy are not necessary for a sole abscess, but must be used aggressively if sepsis of a synovial structure occurs. Pyramidal Disease in Horses (Extensor process fracture, Buttress foot) Fragmentation of the extensor process of the distal phalanx is thought to occur due to trauma, osteochondrosis, or, in large fragments, the presence of a separate center of ossification. Forelimbs are more commonly affected than hindlimbs. The fracture fragments are usually intra- articular but are commonly nondisplaced; they may be adhered to the extensor tendon. The fragments may be incidental findings, but they may also cause lameness. The close association of the extensor process with the distal interphalangeal joint results in secondary arthritis if the fragments are not removed. Fractures can be removed by either arthroscopy or arthrotomy; arthroscopic removal of small fragments carries a good prognosis. With large untreated fractures, an enlargement of the toe region just above the coronary band is usually present, which results in the ―buttress foot‖ or pyramidal appearance to the foot. Systemic anti- inflammatory medication may be beneficial. Quittor in Horses (Coronary sinus) Quittor is a chronic, septic condition of one of the collateral cartilages of the third phalanx characterized by necrosis of the cartilage and one or more sinus tracts extending from the diseased cartilage through the skin in the coronary region. It is seldom encountered today but was common in working draft horses in the past. Quittor usually follows injury to the limb on the medial or lateral aspect of the lower pastern, by means of which infection is introduced into the
  15. 15. traumatized collateral cartilage. This leads to localized sepsis or abscessation of the cartilage. The cartilage may also become infected through a quarter crack. The first sign is an inflammatory swelling over the region of the collateral cartilage, which is followed by sinus formation and intermittent drainage. During the acute stage, lameness occurs. Surgery to remove the diseased tissue is required, but care must be taken not to enter the distal interphalangeal joint. Local or parenteral therapy without surgery is likely to fail. In the absence of any therapy, poor drainage, cartilage necrosis, and recurrent abscessation lead to chronic lameness and extension to deep structures. The prognosis is unfavorable if the disease progresses to involve the distal interphalangeal joint. Quarter Crack in Horses (Sandcrack) Cracks in the hoof wall are thought to occur primarily due to excessive forces placed on the hoof wall and the germinal tissue of the coronary band. It is proposed that shoeing does not allow the hoof wall to expand normally with weight bearing and that quarter cracks commonly form at the placement of the caudal nail because the hoof wall will deform caudal to the nail but not cranial to it. This would place abnormal forces on the laminar tissue and the germinal tissue of the coronary band at that point, resulting in a defect in horn growth that appears as a crack. The same excessive force on a quarter can occur with a shoe in which the branch is too short, resulting in excessive pressure and wall stress at the point where the shoe ends on the quarter. Toe cracks are also thought to occur in shod horses due to the fact that the toe expands abnormally between the cranial-most medial and lateral nails, leading to disruption of tubule formation at the coronary band. A crack in the horn emanating distally from the coronary band is the most obvious sign. Lameness may be present, depending on the degree of wall instability or the presence of submural sepsis. If infection is established, there may be a purulent discharge and signs of inflammation and lameness. Therapy first involves proper trimming of the foot to remove abnormal forces on the coronary band and wall. Once the farrier and veterinarian are satisfied that the foot is responding to the corrective trimming and shoeing, the crack should be debrided, any moisture or sepsis treated with appropriate antiseptic and/or astringent agents until the crack is dry. Multiple wires are then applied across the crack to stabilize it. The wires can be placed either around sheet metal screws placed in the hoof wall on either side of the crack or through small holes drilled through the horn of the hoof wall on each side and exiting through the crack. The crack can be filled with either a resilient acrylic or putty, but it is critical that there be no moisture or sepsis present. Fenestrated tubing can be placed between the deepest aspect of the crack and the acrylic to allow for drainage. The hoof is then bandaged until new horn formation is evident. Scratches in Horses (Greasy heel, Dermatitis verrucosa) Scratches are a chronic, seborrheic dermatitis characterized by hypertrophy and exudation on the caudal surface of the pastern and fetlock. It often is associated with poor stable hygiene, but no specific cause is known. Heavy horses are particularly susceptible, and the hindlimbs are affected more commonly. Standardbreds frequently are affected in the spring when tracks are wet. Scratches may go unnoticed if hidden by the ―feather‖ at the back of the pastern. The skin is itchy, sensitive, and swollen during the acute stages; later, it becomes thickened and most of the hair is lost. Only the shorter hairs remain, and these stand erect. The surface of the skin is soft, and the grayish exudate commonly has a fetid odor. The condition can become chronic, with vegetative granulomas. Lameness may or may not be present; it can be severe and associated with generalized cellulitis of the limb. As the condition progresses, there is thickening and hardening of the skin of the affected regions, with rapid hypertrophy of subcutaneous fibrous tissue. Persistent and aggressive treatment is usually successful. This consists of removing the hair, regular washing and cleansing with warm water and soap to remove all soft exudate, drying, and applying an astringent dressing. If granulomas appear, they can be cauterized. Cellulitis requires systemic antibiotic therapy and tetanus prophylaxis.
  16. 16. White Line Disease in Horses (Hollow wall, Seedy toe, Onychomycosis) White line disease is a condition of the hoof wall in which the hoof wall separates from the underlying laminae at the level of the stratum medium (tubular horn) of the hoof wall. The separation likely starts as a result of abnormal wall stress due to poor foot conformation or trimming (eg, long toe, underrun heels), and can start at the toes, quarters, or heel. Opportunistic bacteria and fungi may be present in the fissures in the hoof wall, sometimes resulting in purulent drainage. The outer surface of the wall may appear sound, but on dressing the palmar surface of the hoof, the inner surface of the wall is mealy, and there may be a cavity due to loss of horn substance. Tapping on the outside of the wall at the toe elicits a hollow sound over the affected portion. Lameness may be present in severe cases, in which loss of support of the distal phalanx occurs. The diagnostic workup includes a thorough physical examination and lateral and dorsopalmar radiographs to assess the extent of separation of the hoof wall. For treatment, corrective trimming is critical to remove abnormal stresses on the hoof wall, followed by removal of the entire extent of the separated hoof wall to the point that firm, healthy adhesion of the hoof wall to the underlying stratum internum can be observed. This hoof wall debridement is performed with a combination of hoof nippers, hoof knives, and a rotary tool. With proper debridement, there is probably no need for antiseptic or astringent treatment. Corrective shoeing is critical to provide adequate support to the remaining foot, while removing stress from the affected regions; a heart bar or egg bar shoe in combination with a resilient putty in the caudal two-thirds of the sole (to provide distal phalanx support) is recommended. Sheared Heels in Horses In sheared heels, there is severe acquired imbalance of the foot with asymmetry of the heels. When viewing the caudal aspect of the foot, one heel is higher than the other side; the higher side commonly has a more vertical hoof wall. When viewed from the side, the coronary band does not gradually angle toward the ground surface in a cranial-to-caudal direction on the higher side. Some horses with sheared heels are lame. Hoof cracks, deep fissuring between the bulbs of the heel, and thrush frequently accompany the problem. Sheared heels most likely occur due to abnormal forces being placed on one side of the foot and are seen frequently in horses with abnormal limb conformation on the affected foot or feet. Corrective trimming and shoeing, in an attempt to restore proper heel alignment and foot balance, are required. A full bar shoe to increase ground surface area while protecting the affected quarter and heel is used. Several shoe resettings may be required before improvement is evident. The prognosis is good in uncomplicated cases if the corrective measures are consistently applied until new hoof growth occurs. Sidebone in Horses (Ossification of the collateral cartilages) Sidebone is ossification of the collateral cartilages of the distal phalanx; it occurs most often in the lateral cartilage. It is most common in the forefeet of heavy horses working on hard surfaces. Repeated concussion to the quarters of the feet is purported to be the cause. Some cases arise from direct trauma. Sidebone is usually an incidental radiographic finding and rarely causes lameness. If sidebone is a cause of lameness, the lameness should entirely subside with a unilateral palmar digital nerve block on the affected side. When lameness is present, corrective shoeing to promote expansion of the quarters and to protect the foot from concussion may be of value. Grooving the hoof wall on the affected side has been reported to help reduce lameness. If sidebone is documented as a cause of lameness, unilateral palmar digital neurectomy may be indicated if the horse does not respond to corrective shoeing and trimming. Thrush Trush is a degeneration of the frog with secondary anaerobic bacterial infection that begins in the central and collateral sulci. The central sulcus is more commonly involved if the horse has sheared heels; the lateral sulci are primarily involved in the majority of cases of thrush. The affected sulci are moist and contain a black, thick discharge with a characteristic foul odor; the borders of the frog are commonly necrotic. These signs alone are sufficient to make the
  17. 17. diagnosis. Although many describe the primary etiology as a moist environment with poor hygiene, it is more likely caused by poor foot conformation or trimming and lack of exercise than from lack of hygiene in the stall. However, a moist environment should be avoided in animals with thrush. Treatment should begin by providing dry, clean flooring and thorough debridement of the frog and sulci. Additionally, the foot needs to be balanced, and affected horses placed on a regular exercise schedule in a dry area. An astringent solution may be applied with daily hoof cleaning. Commercial equine foot formulations that produce chlorine dioxide can also be used. If granulation tissue or sensitive tissue is exposed, astringent solutions should be avoided; a paste made of metronidazole tablets can be applied instead to the affected areas in combination with foot bandaging. The prognosis is usually favorable if changes in shoeing and exercise are made. Fracture of Phalanges and Proximal Sesamoids in Horses Fractures of the first phalanx are not uncommon in racehorses. They may be small ―chip‖ fractures along the dorsal margin of the proximal joint surface, longitudinal fractures or comminuted. Another category involves fragments of the palmar or plantar proximal aspect of the first phalanx, which may be associated with osteochondrosis. Signs of longitudinal fractures involve acute weightbearing lameness after work or a race. There may be little or no swelling initially, but there is intense pain on palpation or flexion of the fetlock. Lameness may be less pronounced with chip or avulsion fractures, but flexion of the joint usually exacerbates the problem. Diagnosis is confirmed by radiography or by scintigraphy for small nonradiographically visible fractures. A number of oblique radiographic views may be necessary to ensure visibility of the fracture line, which may be seen initially as a fine fissure, usually extending distally from the sagittal groove of the proximal phalanx in the dorsopalmar/plantar view. Chip and avulsion fractures can be removed by arthroscopic surgery. Longitudinal fractures can be repaired by internal fixation using two or more cortical bone screws by the technique of interfragmentary compression. Careful attention should be paid to the fracture configuration to ensure that all components are incorporated in the repair. In some circumstances CT may aid an accurate diagnosis. Conservative treatment of severely comminuted fractures involves immobilization with a plaster or fiberglass cast for up to 12 wk, with or without the use of transfixation pins through the third metacarpal/tarsal. However, complications include poor alignment at the fracture site, secondary arthritis, and contralateral laminitis. Fractures of the second phalanx are similar to those of the first phalanx but less common. Treatment and prognosis are similar, although as they tend to be more comminuted, secondary arthritis of the PIP or DIP joints is common. Fractures of the proximal sesamoid bones are relatively common. They are caused by overextension and often are associated with suspensory ligament damage, as in the forelimb or hindlimb of Standardbreds and Thoroughbreds. The lateral proximal sesamoid in the hindlimb of Standardbreds may be fractured as a result of torque forces induced by shoeing with a trailer- type shoe. The fractures may be apical, mid-body, basilar, abaxial, axial, or comminuted, and they may involve one or both sesamoids. Most, apart from some abaxial fractures, are articular. Clinical signs include heat, pain, and acute lameness, which is exacerbated by flexion of the fetlock. There is often hemarthrosis and synovial effusion of the metacarpo/tarso phalangeal joint. Diagnosis is confirmed radiographically. The prognosis is fairly good if small articular fragments are promptly removed by arthroscopy. Apical fractures in adult racehorses removed arthroscopically have an 83% favorable prognosis for return to racing for the hindlimb and 67% for the forelimb. Mid-body fractures require internal fixation using 1–2 lag screws. The prognosis in large basilar fractures is poor, regardless of surgical approach. Complete disruption of the suspensory apparatus, including fractures of both sesamoid bones, is a catastrophic injury accompanied by vascular compromise of the foot; however, some horses can be salvaged for breeding by surgical arthrodesis of the fetlock joint. Osteoarthritis in Horses (Fetlock and Pastern) Osteoarthritis of the proximal interphalangeal joint often creates new bone formation and a bell- shaped appearance to the pastern region. Rarely this may progress to ankylosis. Clinical diagnosis is based on visualization and palpation of soft-tissue thickness and new bone proliferation in the pastern region. Usually, the range of joint movement is restricted, and there
  18. 18. is pain on forced flexion of the involved articular surfaces. Intra-articular and regional diagnostic analgesia identify the pastern region as the site of pain. Radiography confirms the diagnosis in established cases. Anti-inflammatory medication may relieve the signs of lameness temporarily. Surgical arthrodesis of the pastern joint is frequently required to successfully restore performance. Deterioration of articular cartilage within the metacarpal/tarsal-phalangeal joint is a common injury in racehorses and can lead to the development of periarticular osteophytes, enthesiophytes, and joint space collapse. In young, training horses, periosteal bone formation can occur on the dorsal aspect of the distal metacarpus and the proximal aspect of the proximal phalanx, often involving the joint capsule (osselets). Osteoarthritis is often secondary to a primary abnormality such as a chip fracture or osteochondrosis. Treatment can be limited. The use of intra-articular steroids can provide pain relief, but the deterioration of the cartilage is inevitable. In severe, advanced cases, arthrodesis of the joint is necessary to provide pain relief. Osteoarthritis of the proximal interphalangeal joint often creates new bone formation and a bell- shaped appearance to the pastern region. Rarely this may progress to ankylosis. Clinical diagnosis is based on visualization and palpation of soft-tissue thickness and new bone proliferation in the pastern region. Usually, the range of joint movement is restricted, and there is pain on forced flexion of the involved articular surfaces. Intra-articular and regional diagnostic analgesia identify the pastern region as the site of pain. Radiography confirms the diagnosis in established cases. Anti-inflammatory medication may relieve the signs of lameness temporarily. Surgical arthrodesis of the pastern joint is frequently required to successfully restore performance. Palmar/Plantar Osteochondral Disease in Horses This disease affects the palmar aspects of the distal metacarpal condyles and is associated with sclerosis and ultimately fragmentation of the palmar condyles. It is thought to be a stress remodeling response to high-level activity in young racehorses and is associated with lameness referable to the fetlock region. Radiographic signs may be minimal and the changes are identified earliest using gamma scintigraphy, CT, or MRI. Treatment, prior to subchondral bone fragmentation, consists of rest. Sesamoiditis in Horses The sesamoid bones are maintained in position by the suspensory ligament proximally and by a number of sesamoidean ligaments distally. Due to the great stress placed on the fetlock during fast exercise, the insertion of some of these ligaments can tear, which can result in inflammation and pain in this region, known as sesamoiditis. The clinical signs are similar to, but less severe than, those resulting from sesamoid fracture. Depending on the extent of the damage, there are varying degrees of lameness and swelling. Pain and heat are evident on palpation and flexion of the fetlock joint. The radiographic features include periosteal new bone proliferation or osteolytic lesions particularly on the abaxial surface of the affected sesamoid. Radiolucent lines may be seen but must be distinguished from normal vascular channels running through the bone that are evident in young racehorses but rarely associated with pathology. Oblique radiographic views are essential for accurate diagnosis and evaluation. The recommended treatment is a 2- to 3-wk course of phenylbutazone. For mild sesamoiditis, ≥6 mo rest is required; for severe cases, 9–12 mo. The insertion of the suspensory ligaments should be carefully evaluated by ultrasonography for concurrent lesions. Chronic Proliferative Synovitis in Horses (Villonodular synovitis) The cause of this inflammation of the synovial membrane of the dorsoproximal aspect of the forelimb fetlock joints is unknown. It is suspected to be caused by repeated trauma of the thickened synovial plica in the dorsal region of the joint. Affected horses can be of any age. Bilateral involvement has been reported. The dorsal plicae are usually attached by a broad stalk to the dorsal portion of the dorsal proximal pouch of the fetlock joint, are firm and grayish white, and may be circumscribed or lobulated. Erosive bone lesions are typically associated with the mass and, in some cases, may extend to erosion of the articular surface. Microscopically, the lesions consist of dense, well-collagenized stroma lined by synovial cells. Vascularization is prominent, and hyaline change in the stroma and osseous metaplasia are occasionally seen.
  19. 19. Diagnosis can be suspected by palpation. Radiography can be used to identify associated osteolysis of the adjacent underlying condylar bone, and definitive diagnosis of the thickened dorsal soft tissues is made through ultrasonography and arthroscopy. Treatment is by surgical excision via arthroscopy. Digital Sheath Tenosynovitis in Horses Chronic tenosynovitis and associated effusion of the digital flexor tendon sheath is a relatively common condition causing lameness in horses. Initial diagnosis is through palpation revealing heat, pain, and swelling. Sepsis should be ruled out in acute cases. Although some cases of tenosynovitis are primary and respond to conservative therapy with or without treatment of the sheath with corticosteroids, others are secondary to lesions of structures contained within the sheath. Marginal tears of the deep digital flexor tendon and tears of the manica flexoria are the most common tenoscopic diagnoses in surgically treated cases. Treatment of the latter through removal of the affected manica flexoria provides an 80% chance of soundness postsurgery, while debridement of the deep digital flexor tendon marginal tears carries a poor prognosis. Annular ligament constriction can be primary due to desmitis of the ligament or secondary to longstanding tenosynovitis or enlargement of the flexor tendons contained within the fetlock canal. Clinical signs are similar to other causes of tenosynovitis and include pain on palpation, swelling, and lameness, especially following forced flexion of the distal limb. Careful ultrasonographic examination is recommended to assess accompanying pathology. Treatment can be either conservative (ie, steroids) or surgical (transection of a constricting annular ligament). Surgery is best performed tenoscopically, which allows visualization of the remainder of the sheath for primary pathology and assessm Other less common causes of tendon or ligament pathology distal to the fetlock include desmitis of the distal oblique sesamoidean ligaments and lesions of the deep digital flexor tendon within the pastern. Both of these can result in tenosynovitis of the digital sheath and can be diagnosed using ultrasonography or MRI.ent of the degree of constriction. Disorders of the Carpus and Metacarpus in Horses The carpus involves 3 articulations—the radiocarpal (antebrachiocarpal), intercarpal (middle carpal), and carpometacarpal joints. Problems are localized to the carpal area based on lameness, swelling, synovial effusion and pain on palpation, and responses to flexion and diagnostic analgesia. The only clinical evidence of carpal problems may be synovial effusion and minor gait deficits. Visualization and palpation are important to determine the site of swelling in the carpus. Light palpation with fingers with the horse standing is useful initially. Synovial fluid accumulations tend to be more difficult to ascertain when the leg is picked up. Knowledge of the normal anatomic boundaries of the structures is important. The individual carpal bones can be assessed with the carpus flexed; direct palpation of lesions often elicits pain and the degree of carpal flexion possible may be noted. Diagnostic analgesia of the carpal joints is usually done intra-articularly. The antebrachiocarpal and middle carpal joints can be injected easily. The carpometacarpal joint communicates with the middle carpal joint; therefore, local analgesia in the middle carpal joint provides analgesia to the carpometacarpal joint. There is considerable distal outpouching of the carpometa-carpal joint, and with time, analgesia will diffuse into the area of the proximal suspensory ligament. Radiography of the carpus is critical for specific diagnosis of intra-articular fractures, osteochondritis dissecans, subchondral cystic lesions, osteoarthritis, septic arthritis, and osteochondroma of the distal radius. Bucked Shins in Horses (Sore shins, Saucer fractures) Bucked shins is a painful, acute periostitis on the cranial surface of the large meta-carpal or metatarsal bone. It is seen most often in the forelimbs of young Thoroughbreds in training and racing, and less commonly in Standardbreds and Quarter horses. This injury is generally brought about by strains placed on the dorsal cortex during high-speed exercise in young horses in which the bones are not fully conditioned. Microfractures are believed to be involved. It may progress to a cortical saucer fracture or even incomplete longitudinal fracture. In mild cases, subperiosteal hematoma formation and thickening of the superficial face of the cortex may be all that is clinically apparent. There is a warm, painful
  20. 20. swelling on the cranial surface of the affected bone. The horse is usually lame initially, the stride is short, and the severity of the lameness increases with exercise. Rest from training is important until the soreness and inflammation resolve. The acute inflammation may be relieved by anti-inflammatory analgesics and application of cold packs. Screw fixation is the method of choice to treat radiographically demonstrated stress fractures. Subchondral Bone Disease of the Carpal Bones in Horses Degeneration and necrosis of the subchondral bone is common in racehorses and commonly precedes fractures. The condition was initially identified in the proximal articular surface of the third carpal bone and is considered to be a consequence of cyclic trauma. It probably precedes most intra-articular fractures. Recently, the presence of subchondral bone disease in other locations in the carpus has been recognized. Cases on the third carpal bone can be diagnosed radiographically with a skyline view. Other locations are often not seen until arthroscopic examination is done. The treatment is surgical debridement, and the prognosis is relatively good. Desmitis or Sprain of the Inferior Check Ligament in Horses Inferior check ligaments desmitis is a commonly made diagnosis and is often confused with desmitis of the proximal suspensory ligament. Before the use of ultrasonography, the differentiation was difficult. The primary clinical sign is lameness that is alleviated by infiltration of anesthetic behind the proximal aspect of the metacarpus. Anesthetic injected in this area, however, may infiltrate outpouchings of the carpometa-carpal joint in >30% of horses, leading to analgesia of both the carpometacarpal and intercarpal joints. Therefore, a local block of the proximal aspect of the palmar metacarpal nerves is preferable. This condition has been treated conservatively in the past, but sectioning of the ligament, shock wave therapy, and intralesional injection of bone marrow-derived stem cells have become common and achieve relatively good results. Fracture of the Carpal Bones in Horses INTRA-ARTICULAR OSTEOCHONDRAL CHIP FRAGMENTS OF THE CARPUS These are the most common fractures in the carpal joints of racehorses. They occur less commonly in working Quarter horses and sport horses. The primary etiologic factor is trauma, usually associated with fast exercise. Chips may occur on the dorsal aspect of all the carpal bones. In the middle carpal joint, the most frequent site is the distal radial carpal bone, followed by the distal intermediate carpal bone and the proximal third carpal bone. In the antebrachiocarpal joint, the most common location is the proximal intermediate carpal bone, followed by the proximal radial carpal bone, distal medial radius, and the distal lateral radius. The diagnosis is based on clinical signs of synovitis and capsulitis and radiographic demonstration of osteochondral chip fragments. Arthroscopic surgery is the treatment of choice. The overall prognosis is excellent, but the percentage chance of the horse returning to previous performance levels decreases with chronicity and consequent excessive loss of articular cartilage and subchondral bone. CARPAL SLAB FRACTURES Slab fractures extend from one articular surface to another articular surface. In the carpus, slab fractures occur in both frontal and sagittal planes. The most common fracture is a frontal fragment of the radial facet of the third carpal bone, followed by fractures of the intermediate facet and both facets of this bone. When a frontal slab fracture of the third carpal bone occurs without joint collapse, it is considered to be ―routine.‖ The treatment is lag screw fixation (done arthroscopically), and many of these horses return to full athletic activity. Collapsing slab fractures also occur in the carpal bones. The fracture typically involves the third carpal bone, but there is displacement and comminution to the extent that one row of carpal bones tends to collapse. If untreated, the leg progresses to a carpal varus conformation and laminitis develops in the opposite forelimb. Collapsing slab fractures require internal fixation, augmented with cast fixation for up to 6 wk, to minimize later collapse of the joint. Some cases require carpal arthrodesis.
  21. 21. ACCESSORY CARPAL BONE FRACTURES These are less common than other fractures in the carpus. Lameness generally is seen, and there may be synovial effusion in the carpal canal. Radiographs confirm the diagnosis. These fractures are treated conservatively. Bony union will occur in some cases. Fibrous union may enable a horse to return to athletic activity. Fractures of the Small Metacarpal and Metatarsal (Splint) Bones in Horses Fracture of the second and fourth metacarpal and metatarsal bones are not uncommon. The cause may be from direct trauma, such as interference by the contra-lateral leg or a kick, but often accompany or follow a suspensory desmitis and the resulting fibrous tissue buildup and encapsulation of the distal, free end of the bone. The usual site of these fractures is through the distal end, ∼2 in. (5 cm) from the tip. Immediately after the fracture occurs, acute inflammation is present, usually involving the suspensory ligament. A supporting-leg lameness is noted, which may recede after several days rest and recur only after work. Chronic, longstanding fractures cause a supporting-leg lameness at speed. Thickening of the suspensory ligament at and above the fracture site results. The fracture may show a considerable buildup of callus at the fracture site but little tendency to heal. Diagnosis is confirmed by an oblique radiograph. Surgical removal of the fractured tip and callus is the treatment of choice. The prognosis is based on severity of the associated suspensory desmitis, which has a greater bearing on future performance than the splint fracture itself. More proximal splint fractures are usually treated with removal of excess callus. Fracture of the Third Metacarpal (Cannon) Bone in Horses A transverse fracture in the midmetacarpal region can result from direct trauma, usually from a kick. The stress of racing on a hard surface may result in a longitudinally oblique fracture that progresses up the metacarpal shaft from the fetlock and sometimes also involves the proximal sesamoids. Incomplete fractures of the dorsal cortex of the midmetacarpal region can occur as stress-type fractures. Diagnosis is confirmed by radiography; the fissure fractures can be difficult to demonstrate, and a range of oblique views may be necessary. Midmetacarpal fractures may heal with just a cast, although prolonged immobilization may be necessary because union is often delayed. Malunion and the encroachment of callus on surrounding tendons and ligaments cause further problems. Internal fixation with dynamic compression plates and screws is the treatment of choice. Lateral condylar fractures can be treated conservatively by casting, but such articular injuries are best managed by screw fixation using interfragmentary compression if osteoarthritis is to be minimized or avoided. Medial condylar fractures often do not exit and spiral up the bone. In these cases, in addition to lag screw fixation distally, a plate is placed up the remaining metacarpus or metatarsus. Fissure fractures also may show delayed union unless a cortical bone screw is applied. Hygroma in Horses A hygroma is inflammation of an acquired bursa over the dorsal aspect of the carpus. There is accumulation of excessive bursal fluid and thickening of the bursal wall by fibrous tissue. Lameness is not usually present. The diagnosis is made by palpation and visualization. Hygromas can be treated in the early stage with drainage, steroid injections, and bandaging. Later, the implantation of drains is required. Osteoarthritis in Horses (Carpus and Metacarpus) (Degenerative joint disease) In the carpus, osteoarthritis typically appears with chronic thickening of the joint, usually associated with capsular fibrosis. There is a decreased range of motion and sometimes a history of treatment of an acute problem. Radiographic changes develop slowly, and usually the degree of articular cartilage compromise is severe. Cases that can possibly lead to osteoarthritis should be treated aggressively and correctly. Treatment of severe osteoarthritis is largely palliative, but debridement and lavage, followed by intra-articular and systemic therapy, may help.
  22. 22. Osteochondritis Dissecans in Horses Osteochondritis dissecans (OCD) of the carpal joints is uncommon. The typical presentation is a yearling with synovial effusion. Lameness is usually present and can be exacerbated by carpal flexion. Radiographs show the presence of subchondral lucencies typical of OCD, most commonly in the distal radius. Treatment is arthroscopic surgery, but refragmentation and development of osteoarthritis has been seen. The prognosis is fair to guarded. Osteochondroma of the Distal Radius in Horses (Supracarpal exostosis) Osteochondroma formation at the distal end of the diaphysis and metaphysis of the radius is usually seen in young animals. The typical clinical history is swelling of the carpal canal sheath cranial to the ulnaris lateralis after exercise bloody effusion may also be present. At exercise, these horses exhibit moderate lameness. Deep palpation may elicit tenderness and a withdrawal response. Pain is usually elicited with rapid flexion. Diagnosis is generally made by radiography, but ultrasonic examination may be necessary to define the presence of the osteochondroma. The condition can be treated successfully via arthroscopic surgery. The protruding osteochondroma is removed and any concomitant damage to the deep flexor tendon debrided. The prognosis is good. Rupture of the Common Digital Extensor Tendon in Horses This developmental problem is present at birth or is seen shortly after. Foals usually show a carpal flexural deformity or a fetlock flexural deformity. If the condition is not noticed immediately, secondary contracture of the flexor muscle-tendon unit develops. The condition is confirmed by palpation of the swollen disrupted ends of the extensor tendon within the tendon sheath over the carpus. Management involves preventing secondary tendon contracture with the use of PVC splints to prevent knuckling, if appropriate. Healing will occur. Splints in Horses (Metacarpal exostosis) Splints primarily involve the interosseous ligament between the large and small metacarpal bones. The reaction is a periostitis with production of new bone along the involved splint bone. Trauma from concussion or injury, strain from excess training, faulty conformation, imbalanced or overnutrition, or improper shoeing may be contributory factors. Splints most commonly involve the medial rudimentary metacarpal bones. Lameness is seen only when splints are forming and is seen most frequently in young horses. Lameness is more pronounced after the horse has been worked. In the early stages, there is no visible enlargement, but deep palpation may reveal local painful subperiosteal swelling. In the later stages, a calcified growth appears. After ossification, lameness disappears, except in rare cases in which the growth encroaches on the suspensory ligament or carpometacarpal articulation. Radiography is necessary to differentiate splints from fractured splint bones. Complete rest and anti-inflammatory therapy is indicated. Intralesional corticosteroids may reduce inflammation and prevent excessive bone growth. Their use should be accompanied by counterpressure bandaging. In Thoroughbreds, it has been traditional to point-fire a splint, the aim being to accelerate the ossification of the interosseous ligament; however, in most cases, irritant treatments are contraindicated. If the exostoses impinge against the suspensory ligament, surgical removal may be necessary. Subchondral Bone Cysts and Septic Arthritis in Horses Subchondral cysts may be seen in both the distal radius and the carpus. Many, particularly when bilateral and in the ulnar carpal bone, are normal. However, they are commonly symptomatic in the distal radius. They are diagnosed by radiography, and if conservative treatment does not solve the problem, arthroscopic debridement is done. Infectious arthritis of the carpal joints is relatively rare. The most common cause is iatrogenic, in association with intra-articular injections. Horses show severe lameness and marked synovial effusion, as well as more peripheral swelling in the joint. Heat, pain, and synovial fluid changes are obvious. Synovial fluid WBC counts >30,000 and usually 100,000 cells/mm3 , protein levels of 4–6 g/dL in the presence of low viscosity, and a serosanguineous appearance are typical findings.