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 LamenessA 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

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.

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.

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

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 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.

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 HorsesA 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 HorsesBruising 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

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 fracturesNavicular 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.

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 PathogenesisThere 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,

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 FindingsClassically, 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

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.DiagnosisIn 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.TreatmentAcute 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

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.EtiologyThe 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 DiagnosisThe 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.TreatmentBecause 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

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 HorsesPedal 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)

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 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.

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 HorsesIn 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.

ThrushTrush 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 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 HorsesFractures 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 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 HorsesThis 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 HorsesThe 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.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 HorsesChronic 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 HorsesThe 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 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 HorsesDegeneration 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 HorsesInferior 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 HorsesINTRA-ARTICULAR OSTEOCHONDRAL CHIP FRAGMENTS OF THE CARPUSThese 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 FRACTURESSlab 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.

ACCESSORY CARPAL BONE FRACTURESThese 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 HorsesA 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 HorsesA 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.

Osteochondritis Dissecans in HorsesOsteochondritis 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 HorsesThis 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 HorsesSubchondral 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.

Suspensory Desmitis in Horses

Injuries of the suspensory ligament are common injuries in both forelimbs and hindlimbs of horses. Lesions are frequently restricted to the proximal one-third of the ligament, to the body or middle one-third, or to one or both branches.Proximal Suspensory DesmitisThe term proximal suspensory desmitis is restricted to lesions confined to the proximal one-third of the metacarpus. It is relatively common and affects both forelimbs and hindlimbs of horses of

all ages. In contrast to lesions involving the body or branches of the suspensory ligament, there is usually associated lameness, poor performance, or poor action. The condition may be unilateral or, less commonly, bilateral. It sometimes is seen in association with more distal limb pain and is frequently seen in horses with poor mediolateral or dorsopalmar foot balance. Straight hock conformation or hyperextension of the metatarsophalangeal joints may predispose to this type of injury.Lameness can vary in degree from mild to severe and, in early cases, is generally exacerbated by work and improved by rest. Forelimb lameness may be accentuated by flexion of the fetlock and interphalangeal joints but is generally unaffected by carpal flexion, whereas hindlimb lameness may be increased by flexion of the fetlock and interphalangeal joints or by flexion of the hock and stifle joints.In acute cases, there may be localized heat in the proximal metacarpal region with or without periligamentous soft-tissue swelling. In more chronic cases, frequently no palpable abnormality can be detected.Diagnosis is made by local anesthesia and ultrasonographic examination, which usually demonstrates diffuse or central hypoechoic areas with hyperechogenic foci in chronic cases. Treatment in the forelimb is commonly conservative (with intralesional injection of bone marrow-derived stem cells and shock wave therapy being more commonly used). In the hindlimb, these techniques are less successful, although shock wave therapy has improved the overall success rate. Most recently, the use of fasciotomy and neurectomy of the deep branch of the ulnar nerve has become popular. Adjunctive treatments include a graduated program of exercise combined with correction of foot imbalance.

Desmitis of the Body of the Suspensory LigamentThis is principally an injury of racehorses. Injuries usually affect the forelimb of Thoroughbreds, and both forelimbs and hindlimbs in Standardbreds. Soreness on palpation of the forelimb suspensory ligament is quite common in horses with lameness associated with a more distal limb problem; however, only rarely is any structural abnormality of the ligaments identifiable ultrasonographically. The clinical signs vary and involve enlargement of the ligament, local heat, swelling, and pain. Diagnosis is usually based on clinical signs and can be confirmed ultrasonographically. Treatment is aimed at reducing inflammation by systemic NSAID, hydrotherapy, and controlled exercise. Shock wave therapy and stem cell therapy have also been used for these lesions.Desmitis of the Medial or Lateral Branch of the Suspensory LigamentThis relatively common injury is seen in all types of horses in both forelimbs and hindlimbs. Usually only a single branch in a single limb is affected, although both branches may be affected, especially in hindlimbs. Foot imbalance is often recognized in affected horses, and this may be a predisposing factor.The clinical signs depend on the degree of damage and the chronicity of the lesion and include localized heat and swelling. Swelling is often due to local edema of the affected branch. Pain is usually elicited either by direct pressure applied to the injured branch or by passive flexion of the fetlock. Lameness is variable and may be absent.Diagnosis is based on clinical signs and ultrasonographic examination. Only rarely are local analgesic techniques required. Ultrasonography can detect a range of abnormalities, including enlargement, alteration of shape, and alterations in echodensity. Management depends on the severity of the signs and on the breed and use of the horse. Shock wave therapy, as well as stem cell therapy has been used. Strict attention to foot balance is also critical in the management of these lesions. The clinical signs may take many months to improve. The condition may recur.

Synovial Hernia and Ganglion and Synovial Fistulae in HorsesThese conditions are relatively uncommon, but are important in the differential diagnosis of fluid-filled swellings over the dorsal aspect of the carpus. A synovial hernia is a cyst arising from herniation of synovial membrane through a defect in the fibrous joint capsule or fibrous sheath of a tendon. Diagnosis of these conditions is confirmed with contrast radiography; if accessible, the hernia or fistula is surgically repaired.Tearing of the Medial Palmar Intercarpal Ligament in HorsesThis injury, first described in 1990, most commonly involves the medial palmar intercarpal ligament but may involve the lateral palmar intercarpal ligament. A typical presentation is

synovitis and capsulitis unresponsive to therapy or the presence of carpal chip fragments with an untoward amount of lameness. Diagnosis is made arthroscopically, and the treatment is arthroscopic debridement of the torn fibers. The prognosis is excellent in horses with <50% tearing.

Tenosynovitis of the Tendon Sheaths Associated with the Carpus in HorsesThere are several forms of tenosynovitis, including idiopathic, acute traumatic, chronic traumatic, and septic. In the idiopathic form, there is no lameness and synovial effusion localized to the tendon sheath is the only manifestation. It may be seen in the common digital extensor tendon sheath or the extensor carpi radialis tendon sheath; these can be differentiated by knowledge of anatomy. Traumatic forms of tenosynovitis are seen in older animals. In the acute stage, there is fluid distention; in the chronic stage, fibrosis may be present as well. Treatment consists of systemic and local anti-inflammatory therapy (eg, phenylbutazone therapy for 5–7 days). DMSO can be applied topically to the injured area for 7–10 days. In chronic cases in jumpers, surgical debridement may be helpful. Septic tenosynovitis of the carpus is rare. When it is seen, there are acute signs of lameness, heat, and swelling as seen in septic arthritis.

Traumatic Synovitis and Capsulitis in Horses

Traumatic synovitis and capsulitis is inflammation of the synovial membrane and fibrous capsule with no apparent radiographic involvement of bone or other structures. Soft tissues involved can include synovial membrane, fibrous joint capsule, and intra-articular ligaments. Synovitis and capsulitis of the carpus is a common primary clinical condition but also may be accompanied by radiographically unapparent osteochondral damage. The cause is usually considered to be cyclic trauma.Clinical signs include varying degrees of lameness with local heat and swelling. In chronic synovitis and capsulitis, radiographs may show enthesiophytes or osteophytes, but in many instances there are no significant radiographic changes. Treatment is as described under osteoarthritis. The most common treatments are intra-articular corticosteroids, alone or in combination with hyaluronate sodium, as well as systemic NSAID. The use of intra-articular polysulfated glycosaminoglycans is also valuable. Recently, more chronic cases have been treated with autologous conditioned serum. If carpal synovitis and capsulitis do not respond to intra-articular therapy, diagnostic arthroscopy is indicated to eliminate medial palmar intercarpal ligament tearing, osteochondral fragmentation not visible on radiographs, or subchondral bone disease.

Shoulder Disorders in HorsesShoulder lameness in horses is less common than many lay persons expect. Although cases are often described as having a typical gait they are still difficult to diagnose simply from analysis of the animal's walk or trot. However, almost all cases have atrophy of the proximal limb muscles beyond that which would normally be expected for lameness caused by distal limb disease. This is associated not with shoulder pathology per se, but is a feature of proximal limb lameness. Intra-articular anesthesia, medication, and centesis can be accomplished by passing a long needle between the cranial and caudal parts of the lateral tuberosity of the humerus, angling caudodistally, from above. Radiography is limited to the mediolateral projection, with the limb extended, and in some cases oblique projections Ultrasonography can be useful in certain situations.DEVELOPMENTAL DISEASESDevelopmental orthopedic disease manifests in the scapulohumeral joint principally as subchondral cyst-like lesions affecting the glenoid of the scapula or as osteochondritis dissecans of the humeral head. Also, a condition almost exclusive to miniature ponies, caused by dysplasia of the joint and attributable to hypoplasia of the joint surfaces, results in instability and secondary arthritis.

Subchondral Cyst-like LesionsBone cysts may develop in the glenoid, or socket, of the shoulder joint. They may or may not communicate with the shoulder joint and respond variably to intra-articular anesthesia. Although part of the developmental orthopedic disease complex, signs may not be apparent until the animal is mature. In common with other manifestations of this syndrome, lameness may not become a feature until the animal begins work. Occasionally bone cysts may be a cause of

lameness in the older horse, having remained quiescent for most of the animal's life; the reason for these later onset cases is not clear.Diagnosis is made by localization with intra-articular anesthesia, by exclusion of lower limb disease, or occasionally by gamma scintigraphy. Radiographs should document the lesion, although some cysts are too small to be seen.Treatment in young horses consists of rest in the hope that the cyst will remodel to become nonpainful; however, this happens only rarely. Intra-articular medication can provide relief from lameness, but usually only transiently. Some newer disease-modifying preparations show promise and some clinicians favor the use of systemic glycosaminoglycans. Surgical debridement is very difficult in the majority of cases because of the cyst location and articular cartilage damage that causes secondary osteoathritis. Injection of corticosteroids directly into the cyst via an extra-articular approach could be appropriate, but the lack of 3-dimensional imaging of this region in horses makes the approach hard to plan.Osteochondritis DissecansDerangement of cartilage and bone development on the humeral head can result in weakness within the articular cartilage that may lead to erosion or formation of a free flap of cartilage. Typically the caudal part of the head is affected, or at least it is the part most evident on radiographs. In other joints, osteochondritis dissecans often can be treated successfully with arthroscopic debridement. Unfortunately, access to the shoulder joint is severely restricted and in most cases the full extent of the lesion cannot be seen or treated. Clinical resolution in all but the mildest cases in young horses is rare. Rest and various medications have been tried with little documented success.Scapulohumeral DysplasiaSeemingly unique to the miniature breeds, this condition arises from a mismatch between the size of the glenoid and humeral head. This causes instability of the joint and secondary arthritis. Although undoubtedly a developmental problem, probably with a significant degree of heritability, many cases do not present until the animal is an adult. The history is often of sudden onset lameness. On physical examination, proximal limb muscle atrophy is often profound and lameness considerable. These factors, along with the breed disposition and the often present sign of resentment of proximal limb manipulation, make localization straightforward. Radiographs reveal the presence of osteochondrosis and variable subluxation of the scapulohumeral articulation. Oblique views may demonstrate deep erosion of the humeral head in severe cases. The generalized destruction of the joint produces a “hot spot” on a bone scan, if performed. There is no simple treatment. Most cases present at such an advanced stage that even palliative care is impossible; euthanasia on humane grounds should be considered in such situations. Surgical arthrodesis has been described but is rarely performed.

FRACTURESSerious trauma can result in fracture to any part of the shoulder region. However, the main sites affected are the supraglenoid tuberosity of the scapular, the mid to distal scapula, and the proximal humeral metaphysis.Supraglenoid tuberosity fractures, if complete, invariably displace in a craniodistal direction, due to the pull of the biceps. Large fractures can be surgically repaired. This is not easy, however, as the fragments are often difficult to reduce and the implants are difficult to place and prone to failure during recovery from anesthesia or during convalescence. Smaller fragments can be removed, but the involvement of the biceps tendon of origin has to be resected. Very large fragments can involve the joint surface. Cases usually present with severe lameness and a history of trauma. On manipulation, there is often a sense of disarticulation between the lower limb and shoulder as the biceps is disrupted. Crepitus may be felt. In most cases, because the inciting cause is significant trauma, there are other signs such as soft tissue abrasions or swelling that pinpoint the shoulder as the site of pain. Radiographs will reveal the fracture and ultrasonography can be very useful to assess the biceps tendon. Management varies and depends on intended use, age, size of fragment, size of horse, etc. The prognosis for restoration of normal function is guarded. The degree of biceps disruption, along with the severity of lameness and the intended use for the horse, are probably the most important prognostic factors.Mid to distal scapula fractures occur through trauma or, in racehorses, as stress fractures associated with cumulative cyclical fatigue. Trauma can result in complete or incomplete fractures. Radiographs rarely help, because of the difficulty in obtaining diagnostic images of the

area. Ultrasonography can accurately assess the integrity of the bone surface and is the technique of choice. Scintigraphy can also detect the injuries. Comminuted fractures can occur and the prognosis worsens with increased complexity of the fracture. Simple, nondisplaced or minimally displaced fractures usually heal well with rest alone.Ultrasonography can be used to monitor healing. Stress fractures are almost always incomplete and heal very well, carrying an excellent prognosis for return to training. Very rarely, scapula fractures manifest as severe, unstable, comminuted injuries necessitating euthanasia on humane grounds. The clinical appearance is the key to making a decision in these circumstances—although painful, scapula fractures with a good prognosis cause no observable limb instability.Rarely, fractures affect the tuberosities of the proximal humerus and the deltoid tuberosity. The principles described above can be extrapolated to these injuries. The majority heal with conservative therapy and very good outcomes.Stress fractures affect the proximal humerus also, almost exclusively in the caudal metaphyseal region. They are an uncommon but important cause of lameness in racehorses the craniodistal metaphysis of the humerus is also affected. The typical history is one of sudden onset; often moderate to marked lameness closely associated with recent exercise, in an animal usually but not always in faster work. Lameness is usually transient, and the horse generally becomes sound within a short time. If exercise resumes, lameness recurs. Localization is difficult; many are detected following elimination of the lower limb as the source of pain, or with scintigraphy. Radiographs can identify periosteal and endosteal new bone at the site of injury. Recovery is usually uncomplicated and complete with a few weeks' rest. Prolonged confinement may be counterproductive, and light exercise may be introduced surprisingly quickly once the initial painful period has subsided. The injury remains evident on radiographs long after the bone is strong enough to withstand exercise, but a gradual smoothing and resolution of the callus will be seen as remodelling proceeds. Undetected humeral stress fractures can result in failure of the bone during exercise and complete breakdown, necessitating euthanasia.BICIPITAL BURSITISThe tendon of the biceps brachii runs over the cranioproximal humerus, protected by a synovial bursa. Inflammation of this structure can cause lameness and is usually secondary to a more serious inciting cause. Trauma to the proximal humerus, cystic lesions in the underlying bone, and injury to the tendon itself will cause secondary bursitis; it is important to recognize the primary lesion and treat appropriately. Occasionally, idiopathic primary bursitis arises and responds very well to medication of the bursa with corticosteroids. Bacterial contamination and, rarely, fungal infections can cause bicipital bursitis. In most cases, a wound in the vicinity of the bursa alerts the clinician to this possibility but, very rarely, closed sepsis can occur. Treatment for septic bursitis follows the same pattern as for other synovial structures. Radiography and ultrasonography complement each other in the diagnosis and management of primary and secondary bursitis. Repeat examinations may be necessary if a primary lesion cannot be detected, as it may become obvious with time. Scintigraphy is useful in cases in which the primary lesion remains elusive, because small areas of bone damage or cavitation can go undetected radiographically.INFECTIONSepsis of the shoulder joint occurs most commonly as a result of penetrating injury. Diagnosis and treatment proceed as for other joints. In foals infection can spread hemato-genously and become established in the growth plates or ends of the bones. These infections, provided they are not associated with contamination of the synovial structures, can be treated with high levels of antimicrobials systemically before resorting to surgical intervention. Methods of providing high quantities of antimicrobials at the site of infection exist.SUPRASCAPULAR NEUROPATHY(Sweeney)This syndrome describes the physical appearance of the horse's shoulder. It is not a diagnosis in itself, as there are a number of potential causes. The most common cause is injury to the suprascapular nerve.All cases have atrophy of the supraspinatus and infraspinatus muscles that cover the scapula. This results in the scapular spine becoming prominent—in severe cases the muscles virtually disappear. The atrophy is unusual in that it is often profound and very localized, which are hallmarks of an injury to a single lower motor nerve. The nerve involved is the suprascapular. Although the site of damage is rarely documented clinically, most cases involve trauma to the

cranial shoulder at the point where the nerve is exposed to potential compression as it courses over the cranial aspect of the scapula. The severity of damage determines the degree of atrophy and the chances of recovery. If nerve function is severely compromised, the shoulder joint becomes unstable and the joint “pops out” sideways as the horse bears weight. This subluxation does not appear overtly painful to the horse but does have significant implications for the longterm health of the joint and the horse's athletic career.Therapy is aimed at maintaining muscle health during the period of nerve recovery and maximizing neurogenesis. Horses should be restricted to stable rest or a very small paddock. Complete immobilization may negatively impact the nerve and muscles, but activity probably hastens joint degeneration. A surgical procedure for removing part of the scapula over which the nerve courses has been described, aiming to provide optimal conditions for nerve recovery. This should be considered, but its usefulness is open to debate. Muscle stimulation, under the guidance of a trained physiotherapist, will help to limit muscle fibrosis and may encourage nerve regeneration. The vast majority of cases seem to be a result of neuropraxia or axonotmesis and will recover function with time. However, this process can take many months and frequently some loss of muscle bulk will remain. The prognosis seems most affected by duration of injury before diagnosis, degree of atrophy at diagnosis, and willingness of the owner to perform time-consuming physical treatments for many months.Other causes of sweeney include disuse atrophy, brachial plexus injury, and caudal cervical disease resulting in spinal nerve radiculopathy. Careful assessment of the muscles involved and radiography of the neck and shoulder will aid differentiation. Scintigraphy is useful for rapid screening of the proximal limb and cervical and thoracic vertebra for damage that may have an adverse effect on prognosis.OSTEOARTHRITISDegenerative joint disease affecting the shoulder joint poses the same problems here as it does elsewhere. If no primary cause is identified that is amenable to correction and if radiographic signsare established, it is safe to assume that cartilage destruction is well underway. Signs can be ameliorated, but not cured, with the use of anti-inflammatory, analgesic, and disease-modifying therapies.COLLATERAL LIGAMENT INJURYMost commonly detected laterally, probably for biomechanical and imaging reasons, these injuries can be detected with ultrasonography. Medial collateral ligaments are more difficult to image but can be assessed. Radiographs may document new bone associated with injury. A number are found by scintigraphy, associated with a “hot spot” even in the absence of radiographic changes. Prognosis depends on the severity of the injury. At this time, no proven therapies exist to augment ligament healing. A number of treatments have been tried, including medication, systemic disease-modifying drugs, and extracorporeal shockwave therapy.

Bone Spavin in HorsesBone spavin refers to osteoarthritis or osteitis of the distal intertarsal and tarsometatarsal articulations, and occasionally the proximal intertarsal joint. Lesions involve degenerative joint disease, particularly on the dorsomedial aspect of the hock with periarticular new bone proliferation, which eventually leads to ankylosis. Lytic lesions, which are part of the degenerative joint disease complex, can occasionally be seen; animals with such lesions are difficult to treat. Although bone spavin usually causes lameness, this may be obscured if the lesions are bilateral. Among the different theories proposed to explain this condition, poor hock conformation, excessive concussion, specific athletic events and mineral imbalance are the most frequently mentioned. All breeds can be affected, but it is most prevalent in dressage horses, Standardbreds, and Quarter horses.The lame horse tends to drag the toe. The forward flight of the hoof is shortened, and hock action is decreased. Frequently, horses “warm out” of the lameness after a few minutes' work, but in some cases the lameness persists because the bone lesions involve the articular surfaces. The heel may become elongated. Standardbreds develop soreness in the gluteal musculature secondary to spavin. In advanced cases, the bony proliferation may be visible on the distal dorsomedial aspect of the hock. When standing, the horse may rest the toe on the ground with the heel slightly raised. The lameness often disappears with exercise and returns after rest. The spavin test may be a useful aid to diagnosis but, because of the reciprocal apparatus in the rear limb, this test is not specific for this condition or even this joint. In so-called

occult spavin, there are no visible or radiographic lytic lesions or exostoses. Local anesthesia of the individual tarsal joints is necessary to localize the exact site of pain responsible for the lameness.The disease is self-limiting, ending with spontaneous ankylosis of the affected joint(s) and a return to soundness. In the early stages, intra-articular injection of corticosteroids or sodium hyaluronate may be beneficial. NSAID eliminate or reduce the clinical signs. Working the horse after this treatment is aimed at accelerating ankylosis and resolution of lameness. Chemical arthrodesis using monoiodoacetate or alcohol has been advocated as a less traumatic management option. These agents induce a severe arthritis, and NSAID must be administered for a few days. Additionally, it must be confirmed prior to the injection of the agent that there is no communication with the talocrural joint. Otherwise, the talocrural joint will also lose its function. Surgical arthrodesis is another means of accelerating ankylosis of the affected joint. Insertion of oblique screws crossing the tarsometatarsal and distal intertarsal joints facilitate faster resolution of the lameness. These screws can be inserted through surgical plate or next to them. If only the plate and not the screws bridge the joint(s) involved, the repair is mechanically less stable. Preparation of fan-shaped holes along the involved joint surface(s) has been advocated alone or in conjunction with a plate. The drill bit should not be swiped along the joint surface to remove as much cartilage as possible; this technique induces a severe lameness as a result of the instability created. Cunean tenotomy is commonly used but of questionable value by itself. Deep-point firing used to be advocated for hastening ankylosis, but it is very doubtful that it has any beneficial effect beyond encouraging rest. Corrective shoeing by raising the heels and rolling the toe may help but is unlikely to eliminate lameness on its own.

Curb in HorsesCurb refers to a thickening or bowing of the plantar tarsal ligament due to strain. This ligament may become inflamed and thickened after falling, slipping, jumping, or pulling. This problem is most common in Standardbreds, in which poor conformation of the hock is a predisposing factor. There is an enlargement over the caudal surface of the fibular tarsal bone ∼4 in. (10 cm) below the point of the hock. It is easily seen when observing the horse from the side. A recently formed curb is associated with acute inflammation and lameness. The horse stands and favors the limb with the heel elevated. In chronic cases, there is rarely any lameness or pain.If the curb is due to acute inflammation, cold packs and rest are indicated. Little can be done to overcome the curb that is secondary to poor conformation. Fortunately, the problem seems to be self-limiting, without lasting effects on performance.A curb-like lesion can be observed in foals with incomplete ossification at the time of birth. If these conditions are not properly managed with tube casts or splint bandages and the foal confined to box stall rest, the precursor cartilage still present in the small tarsal bones may become thin and eventually rupture, resulting in a partial forward collapse of the tarsus and the appearance of the curb-like contour. These animals are lame, but once ankylosis of the small tarsal joints occurs, which may take months, the lameness disappears.

Displacement of the Superficial Flexor Tendon from the Point of the Hock in HorsesDamage to the medial attachment of the superficial flexor tendon as it passes over the tuber calcanei can cause a lateral luxation of the tendon. The injury occurs as a result of sudden flexion of the hock, and the tendon can occasionally slip to the medial aspect of the hock. Initially, there is lameness in the limb, with local heat and swelling. Treatment involves rest for ≥3 mo, possibly with application of a cast. The lameness improves, but the horse may be left with a permanently displaced flexor tendon and a rather jerky hock action. There is usually no difficulty during fast exercise or jumping but dressage movements may be affected. Surgical treatment has been reported in a limited number of cases. The results vary and are not likely to be favorable in larger horses.

Hindlimb Tendon Ruptures in HorsesLaceration of the entire Achilles tendon involving both the gastrocnemius and superficial flexor tendons is rare. The hock drops toward the ground and is unable to bear weight. The prognosis is grave.Gastrocnemius muscle rupture is more common and can result from excess stress applied to the hock. It can be bilateral and some weight can be borne, but there is excess flexion of the hock, which makes walking difficult. There is no satisfactory treatment. Splinting the limb and

slinging the horse have been tried and have resulted in some success. Generally, foals with this condition have a better prognosis.Injuries to the long and lateral digital extensors, frequently accompany hindlimb lacerations. If one tendon is involved, the prognosis is usually good. If both extensor tendons are severed, the horse may be left with a gait deficit for performance, but it may be useful for pleasure riding or for breeding. Conservative treatment leads to wound healing, but surgical repair and casting should be considered if both tendons are severed or if performance status is desired.The superficial and deep flexor tendons sometimes rupture as a racing injury or accompany lacerations. These are serious injuries with marked lameness and varying degrees of overextension of the fetlock and pastern. Treatment involves surgical repair with splinting and casting the limb, but the prognosis is poor for future performance.

Rupture of the Peroneus Tertius Muscle in HorsesInjury to the peroneus tertius muscle affects the stay apparatus of the hindlimb and disrupts the reciprocal action of the stifle and hock joints. This condition may also develop when a horse is kept in a full-limb cast for an extended period. The most characteristic diagnostic feature is the ability to extend the hock and flex the stifle simultaneously. The horse is lame but usually able to bear weight on the limb. The affected hindlimb exhibits a jerking motion as it is brought forward. Conservative treatment consisting of prolonged rest is indicated; the prognosis is favorable.

Stringhalt in HorsesStringhalt refers to a myoclonic affliction of one or both hindlimbs seen as spasmodic overflexion of the joints. The etiology is unknown, but lesions of a peripheral neuropathy have been identified in the sciatic, peroneal, and tibial nerves. Severe forms of the condition have been attributed to lathyrism the USA and possibly to flat weed intoxication in Australia. Horses of any breed may be affected; the condition is rare in foals.All degrees of hyperflexion are seen, from the mild, spasmodic lifting and grounding of the foot, to the extreme case in which the foot is drawn sharply up until it touches the belly and is then struck violently on the ground. In severe cases, there is atrophy of the lateral thigh muscles. In Australian stringhalt and lathyrism, the condition may be progressive, and the gait abnormality may become so severe that euthanasia is warranted.Mild stringhalt may be intermittent. The signs are most obvious when the horse is sharply turned or backed. In some cases, the condition is seen only on the first few steps after moving the horse out of its stall. The signs are often less intense or even absent during warmer weather. Although it is regarded as unsoundness, stringhalt may not materially hinder the horse's ability to work, except in severe cases when the constant concussion gives rise to secondary complications. The condition may also make the horse unsuitable for equestrian sports. Diagnosis is based on clinical signs but can be confirmed by electromyography. If the diagnosis is in doubt, the horse should be observed as it is backed out of the stall after hard work for 1–2 days. False string-halt sometimes appears as a result of some temporary irritation to the lower pastern area or even a painful lesion in the foot. The occasional horse with momentary upward fixation of the patella may exhibit a stringhalt-like gait.When intoxication is suspected, removal to another paddock may be all that is required. Many of these cases apparently recover spontaneously. In chronic cases, tenectomy of the lateral extensor of the digit, including removal of a portion of the muscle, has given best results. Improvement may not be evident until 2–3 wk after surgery. Prognosis after surgery is guarded—not all cases respond. This is not surprising because the condition is a distal axonopathy. Other methods of treatment include large doses of thiamine and phenytoin.Thoroughpin in HorsesThoroughpin refers to a distention of the tarsal sheath of the deep digital flexor tendon just above the hock. It is characterized by plantar fluid-filled swellings visible on both medial and lateral sides proximal to the tibiotarsal joint, which distinguish it from bog spavin. It is usually unilateral and varies in size. The lesion is referred to as a tenosynovitis of traumatic origin, but it may not be associated with any detectable inflammation, pain, or lameness. It essentially constitutes a blemish and so is of major clinical importance in show horses. Treatment is by withdrawal of the fluid and injection of hyaluronate and/or a long-acting corticosteroid, which may need to be repeated until the swelling does not recur.

Fractures of the Third Metatarsal Bone in Horses

Generally, the same type of fractures can be acquired as in the third metacarpal bone. Kicking injuries or other external influences are usually responsible for the development of the different types of shaft fractures Lateral condylar fractures occur more frequently in Standardbred horses and may be present bilaterally with marginal lameness; medial condylar fractures are rare. Nondisplaced, incomplete fractures of the proximal third of the third metatarsal bone that extend into the tarsometatarsal joint are seen only in this bone. Stress fractures that occur in the forelimb do not occur in the hindlimb. Horses with third metatarsal bone fractures are usually severely lame. Weight bearing and axial deformation during loading depend on the type of fracture(s) present. Diagnosis is usually confirmed by radiography and/or other diagnostic imaging techniques.Fissure fractures may be treated by stall rest, bandaging, and maintenance in a sling to prevent the animal from lying down. This type of management prolongs recovery time but is an option. Other conservative management techniques, such as cast application, are possible in certain fractures, but are no longer advocated for several reasons. They prevent early active motion and induce fracture disease and, frequently, pressure sores at predilection sites and may lead to rupture of the peroneus tertius tendon if a full cast is applied. Additionally, many horses do not tolerate casts that prevent flexion of the talocrural joint. Internal fixation is the treatment of choice. Locking compression plates allow solid, rigid fixation of most load-preventing fractures. The plate allows the introduction of regular cortex screws and where desired, locking head screws. Condylar fractures and proximal incomplete fractures of the third metatarsal are best treated by means of cortex screws inserted in lag fashion through stab incisions. With this type of treatment, the fragment can be compressed onto the parent portion of the bone to facilitate rapid bone healing, usually without callus formation. If the horse is to be returned to athletic activity, plate removal 5–6 mo postoperatively is indicated. If 2 plates were applied, staggered removal is performed 3 mo apart. In most cases, fractures repaired only with cortex screws do not require implant removal after healing.

Large Wounds in the Proximal Metatarsal Region in HorsesTrauma to the dorsal and proximal metatarsal region is relatively frequent and may result in severe skin, tendon, and ligament injury; underlying bone may also be affected. Careful examination of the wound and the surrounding structures is required to detect involvement of additional structures, such as the joints. Initial repair of the skin defect should be attempted after thorough debridement and may require an expansion mesh technique and facilitation of drainage. The wound should be bandaged and the tarsal region immobilized for the first 2 wk. Wound dehiscence is common and necessitates removal of all suture material, an additional debridement, and application of a moist bandage. The wound has to heal by second intention and will always be recognizable by the scar tissue that will form. Scars may limit the motion of the talocrural joint. Sequestration of bone is common over the next 2 mo. To facilitate healing, bone fragments must be surgically removed once they have separated from the underlying bone. Complete healing takes months and requires prolonged medical attention.

Subchondral Cystic Lesions in HorsesSubchondral cystic lesions most commonly occur in the stifle in the medial femoral condyle. Osseous cyst-like lesions may also occur in the proximal tibia. The pathogenesis of these cysts is poorly understood, but they may occur after trauma to the articular surface or as a result of osteochondrosis. Lesions often present in young horses but can occur at any age. The severity of lameness varies from mild to severe and may be acute in onset. Lameness may be intermittent, particularly in older horses. In some horses there is mild effusion of the medial femorotibial joint but in many horses no localizing signs are evident. Intra-articular anesthesia of the femorotibial joints may produce partial improvement.Diagnosis is usually confirmed by radiography. Medial femoral subchondral cystic lesions are most evident on caudocranial projections and may appear as a variably sized round or oval radiolucent defect in the subchondral bone. Some lesions are surrounded by an obvious sclerotic rim. In some horses only a very small defect is evident radiographically in the medial femoral condyle; this may be a precursor to subchondral cystic lesions. Defects in the surface of the medial femoral condyle may be evident ultrasonographically in some horses. Subchondral cystic lesions in the proximal tibia are usually smaller and most evident on lateral, lateral oblique, or caudocranial radiographic projections.

Nonarticular osseous cyst-like lesions or small lesions may respond to conservative treatment, including rest, systemic NSAID, and intra-articular corticosteroids. If horses do not respond to conservative treatment, surgery is indicated. Some surgeons advise injection of corticosteroids into the lining of the cyst under arthroscopic or ultrasonographic guidance to decrease the shedding of inflammatory enzymes and mediators into the joint. Others advise arthroscopic debridement of the cyst to remove the contents and lining.The prognosis for return to athletic function in horses with subchondral cyst-like lesions of the medial femoral condyle following injection of the lining of the cyst under arthroscopic guidance has been reported to be fair, with 64% returning to athletic use in one study irrespective of the age of the animal. The prognosis for return to athletic function following debridement of the cyst seems to vary with the horse's age. The prognosis for athletic soundness in horses <3 yr old was better (∼64%) than in horses >3 yr old (35%) at the time of surgery in one large, multicenter retrospective study.

Cranial and Caudal Cruciate Ligament Injuries

Complete or partial rupture of a cruciate [caudal] ligament resulting in severe lameness and joint instability.

Lameness depends on the severity of injury. Effusions of the femoropatellar or femorotibial joints are sometimes present. Lameness is usually improved by intra-articular anesthesia of the femorotibial joints.

Diagnosis:

Confirmed by arthroscopic examination Ultrasonography

Treatments

Conservative treatment Rest Systemic NSAIDs Intra-articular corticosteroids

Prognosis

The prognosis for return to athletic function depends on the severity of injury. Horses with complete rupture have a grave prognosis. Horses with moderate to severe injuries have a poor prognosis for return to athletic

function, while horses with mild injuries have a fair prognosis.

Collateral Ligament Injuries

Rupture or sprain of the medial or lateral collateral ligaments of the stifle is usually the result of an acute traumatic episode in which the distal limb is forced medially or laterally, thereby stressing the ligaments.

Rupture or sprain is more common in the medial collateral ligament thanin the lateral collateral ligament.

Concurrent injury of the menisci or cruciate ligaments is common, particularly in severe injuries. Lameness depends on the severity of the injury but is usually quite severe initially.

Clinical Signs

Localized edema Joint effusion particularly in the acute stages.

***Clinical signs usually improve within a few days unless there is significant joint instability.

If complete ligament rupture has occurred, stressed caudocranial radiographs of the stifle may demonstrate joint widening on the affected side.

Enthesiophyte formation at the origin or insertion of the ligament is evident radiographically in chronic cases.

Diagnosis

Confirmed by ultrasonographic examination

Treatment

Mild sprains may be treated conservatively with stable rest and anti-inflammatory medication for 6–8 weeks, followed by a controlled, ascendingexercise rehabilitation program for a further 6–8 weeks.

Prognosis

Horses with mild sprains and no joint instability have a fair prognosis for return to athletic use.

The prognosis for horses with severe injury is poor.

Intermittent Upward Fixation of Patella and Delayed Patella Release

Occurs when the medial patellar ligament remains hooked over the medial trochlear ridge of the femur and locks the reciprocal apparatus with the limb in extension.

A horse with upward fixation of the patella stands with the hindlimb fixed in extension with the fetlock flexed. The leg will usually release with a sudden snap or jerking movement.

In milder conditions, there is delayed release of the patella during limb protraction, most commonly evident as the horse moves off or in downward transitions appearing as a jerky movement of the patella.

Horses with recurrent upward fixation or delayed release of the patella may develop chronic, low-grade lameness due to stifle soreness and may be reluctant to work.

Most commonly seen in young horses and ponies, particularly if they are in poor body condition and poorly muscled.

May also occur in older horses that have had trauma to the stifle region, particularly if horses are stabled or have been inactive.

Predisposing Factor

Straight hindlimb conformation

Diagnosis

Based on recognition of typical clinical signs

Management

Upward fixation of the patella may be induced by pushing the horse backward or manually pushing the patella proximally.

Radiographs of the stifle should be taken in horses with femoropatellar joint effusion and lameness to establish concurrent or secondary pathology.

To release an upward fixated patella, the horse should be pushed backward while simultaneously pushing the patella medially and distally. Alternatively, pulling the limb forward with a rope around the pastern may unlock the patella.

If upward fixation of the patella is intermittent and not causing lameness, a conditioning program should be instituted: lungeing or riding of the horse, appropriate to its age and type, as well as ensuring an adequate plane of nutrition, good dentistry, and anthelmintic administration.

Remedial hoof trimming to ensure that the foot is well balanced.

Improve with maturity and conservative treatment, although signs may recur if the horse undergoes prolonged stall rest.

Medial patellar ligament desmotomy is indicated in horses that fail to respond to conservative treatment or in horses with lameness caused by upward fixation of the patella.

Medial patellar ligament desmotomy is most often performed in the sedated horse under local anesthesia or general anesthesia.

Following surgery, the horse should be restricted to stable rest for 2 months to reduce the risk of complications.

Complications

Fragmentation of the apex of the patella - most common complication following surgery. Lameness Local swelling Patella fracture

Prognosis

The prognosis following medial patellar ligament desmotomy is generally considered to be good, with recurrence of the condition rare.

Contraindication

Stable rest and prolonged standing

Fragmentation of the Patella

Usually occurs secondary to medial patellar desmotomy for the management of upward fixation of the patella.

Lesions are believed to occur due to patellar instability as a result of the surgery. The severity of lameness varies from mild stiffness to moderate lameness. A proximal limb flexion test usually exacerbates lameness and femoropatellar joint

effusion is usually present.

Diagnosis

Confirmed by radiography

Treatment

Arthroscopic debridement of the apex of the patella and removal of the osteochondral fragments - treatment of choice.

Prognosis

Prognosis is reasonable but depends on the severity of the condition.

Patellar Luxation

Lateral luxation of the patella is a rare, inherited condition in foals caused by a recessive gene.

Luxation of the patella in adult horses is unusual and likely to be traumatic in origin. Lateral luxation is more common than medial luxation and may be more likely in horses

or foals with hypoplasia of the lateral trochlear ridge of the femur. The condition may be unilateral or bilateral and varies in severity from intermittent

luxation that readily reduces to persistent luxation that cannot be reduced. Severely affected foals are unable to extend the stifle and adopt a characteristic

crouching position. If the condition is less severe, foals or horses may be reluctant to flex the stifle and

demonstrate a stiff hindlimb gait.

Diagnosis

Confirmed by radiography

Treatment

Conservative treatment

Prognosis

Prognosis in adult horses and horses with concurrent osteoarthritis is poor. The prognosis for athletic function in foals may be slightly better.

Patellar Ligament Injuries

Rare but may be seen in jumping horses. The middle patellar ligament is the most commonly affected. Lameness is may be severe in acute cases.

Clinical signs

Femoropatellar joint effusion Periligamentous thickening Edema - inconsistent findings

Diagnosis

Confirmed by ultrasonography.

Treatment

Prolonged rest up to 6 months

Gonitis and Osteoarthritis

Gonitis is the inflammation within the stifle joint. Mild to moderate inflammation of the femorotibial and femoropatellar joints of unknown

origin. Synovitis and capsulitis may result from athletic sprain of the joints. Mild trauma to the articular cartilage, menisci, or any of the ligaments of the stifle may

produce mild to moderate synovitis. Mild synovitis usually responds to rest and intra-articular and systemic anti-inflammatory

drugs. If joint inflammation and lameness persist, further diagnostic investigation and

arthroscopic examination are advisable to assess concurrent or causative injuries and to prevent ongoing degenerative joint disease and the development of osteoarthritis.

Osteoarthritis of the femorotibial or femoropatellar joints may follow any of the causes of stifle lameness described and usually results in persistent lameness of varying severity.

Diagnosis

Confirmed with intra-articular anesthesia and radiography.

Radiographic changes

Periarticular remodeling with osteophyte formation and remodeling of the joint margins. Changes in the subchondral bone. Narrowing of the joint space. Dystrophic mineralization of the soft tissues.

Prognosis

Prognosis for athletic soundness in horses with osteoarthritis of the stifle is poor.

Treatment

Usually palliative

Fractures

FRACTURES OF THE PATELLA

Usually result from direct trauma, most commonly when a horse is kicked by another horse or hits a fixed obstacle while jumping.

Sagittal fractures of the medial pole of the patella are most common. These fractures are usually intra-articular and involve the attachment of the parapatellar fibrocartilage of the medial patellar ligament.

Complete horizontal fractures are rare but are considered serious injuries because of fragment distraction due to the massive pull of the extensor muscles.

Fracture of the patella usually results in marked lameness initially, with swelling and edema over the patella and effusion of the femoropatellar joint.

In less severe or nonarticular fractures, lameness may improve within a few days.

Diagnosis

Confirmed by radiography

Management

Conservative treatment with stable rest for 6–8 weeks for horses with small, nondisplaced, nonarticular fractures. Good prognosis for return to athletic function.

Articular fractures of the medial pole of the patella can be removed arthroscopically or via an arthrotomy. Good prognosis.

Larger mid-body sagittal or horizontal fractures require repair by internal fixation. Prognosis depends on fracture conformation.

FRACTURES OF THE TIBIAL TUBEROSITY

Usually result from direct trauma. Fracture configuration may range from small fragments off the cranial proximal part of

the tuberosity to large fractures of the whole of the tuberosity extending into the femorotibial joints.

Fracture of the tibial tuberosity usually results in marked lameness initially with localized swelling and edema.

Lameness will often improve within a few days.

Diagnosis

Confirmed by radiography

Treatment

Conservative treatment for small and nondisplaced fractures followed by stable rest for 6–8 weeks. During the first 2–3 weeks the horse should be prevented from lying down by tying or the use of slings to prevent fragment displacement.

Larger, intra-articular fractures should be repaired by internal fixation.

Prognosis

Good if appropriately managed.

FRACTURES OF THE FEMORAL CONDYLES AND FEMORAL TROCHLEAR RIDGES

Usually the result of direct trauma. Traumatic fragmentation of the femoral condyles or trochlear ridges usually results in

acute onset, moderate to severe lameness with joint effusion.

Diagnosis

Confirmed by radiography

Treatment

Surgical [arthroscopically and arthrotomy] removal of the fracture fragments to prevent the development of osteoarthritis.

Prognosis

Usually considered to be good as long as there is no significant concurrent soft tissue damage.

Large, intra-articular, displaced fractures in adult horses have a grave prognosis.

Disorders of the Hip

Relatively rare causes of lameness in horses. Most cases are traumatic in origin, secondary to falls or being cast in recumbency,

although septic arthropathies and developmental disorders of the joint have been occasionally reported.

Secondary osteoarthritis of the coxofemoral joint is a common result no matter what the etiology of the primary disease.

Lameness is the predominant presenting clinical sign of any coxofemoral disease. In severe cases, the horse will often stand with the limb partially flexed with marked

atrophy of the muscles of the quarters. In cases of coxofemoral subluxation, the leg will be held in a semi-flexed position with an

obvious outward rotation of the stifle and toe and an inward rotation of the point of the hock.

In complete coxofemoral luxations, the same limb position is observed. Most horses with coxofemoral pathology show some pain on proximal limb flexion or

abduction. Hematoma or alteration in the bony architecture are palpable per rectum. Intra-articular local anesthesia of the coxofemoral joint is commonly used to identify the

joint as the cause of lameness, particularly in cases of chronic lameness.

Definitive Diagnosis

Requires some diagnostic imaging [bone scanning (nuclear scintigraphy) is commonly used].

Percutaneous ultrasonography Radiography - require general anesthesia Arthroscopy

Luxation of the Coxofemoral Joint

Relatively rare in horses due to the strong ligamentous support provided to the joint by the round ligament and the accessory femoral ligament, as well as the fibrocartilaginous lip that surrounds the acetabulum.

Usually secondary to trauma.

Management

Best managed by closed reduction under general anesthesia

Prognosis

Very guarded.

Disorders of the Back and Pelvis

Back problems are a major cause of poor performance and gait abnormalities in sport and race horses.

Once back pain is suspected or established in a horse, identification of the cause requires imaging procedures.

Diagnosis

Ultrasonogrpahy Radiology

Spinal Processes and Associated Ligaments

KISSING SPINES

Most common location of lesions is the vertebral segment between T10 and T18, although kissing spines are not rare between L1 and L6.

Abnormal findings can be seen in the dorsal part of the spinous processes where their identification is easy including kissing and overriding lesions.

Different Grades: Grade 1: Narrowing of the interspinal spaceGrade 2: Densification of the margins Grade 3: Bone lysis adjacent to the marginsGrade 4: severe remodeling

Abnormal findings can also be seen in the ventral part of the spinous processes and may involve the interspinal ligaments or be associated with osteoarthrosis of the articular processes.

The incidence of kissing spines seems to vary according to the horse discipline and biomechanical effects of specific gaits and exercises on the back.

Intermediate frequency and signs are observed in sport horses. Kissing spines can be found in performance race and sport horses without back pain

and even with normal thoracolumbar active and passive mobilization.

Diagnosis

Aided by injection of local anesthetic into the affected interspinous spaces.

Management

Local injections of steroids Mesotherapy Shockwave therapy and rehabilitation using tolerated exercises

FRACTURES

Multiple fractures of the spinous processes of T4–T10 are sometimes seen in horses that have reared and fallen over backward.

The summits and centers of ossification are fractured and displaced laterally. After the initial pain and local reaction have subsided, recovery is often satisfactory. Usually, there is no permanent effect on performance, but a persistent deformation of

the withers may require use of a special saddle.

DESMOPATHIES(Supraspinal ligament injuries)

Acute or subacute desmopathies induce dorsoventral or transverse thickening of the ligament, reduced echogenicity, and severe alteration of the linear pattern.

They can be found in the median plane or asymmetrically. In old or chronic injuries, the ligament often remains thicker with a reduced echogenicity

and an irregular architectural pattern. Alteration of the bone surface of the top of the spinous processes indicates insertional

desmopathy (enthesopathy) of the supraspinous ligament.

Articular Process-Synovial Intervertebral Articulation Complexes (AP-SIVA)

Located dorsally to the vertebral canal and is composed of the caudal articular process of one vertebra, the synovial joint located at the base of the interspinal space, and the cranial articular process of the following vertebra.

Eight types of abnormal radiographic findings have been identified in the AP-SIVA complexes of the equine thoracolumbar spine.

AP-SIVA lesions are much more likely to be associated with back pain than kissing spines or any other vertebral lesions.

Vertebral Bodies and Disks

The most common lesion of vertebral bodies and disks is ventral, ventrolateral, or lateral bony proliferation (vertebral spondylosis).

It is mainly found in the midthoracic area (mostly between T10 and T14) but can also be observed in the lumbar area.

Congenital abnormalities with vertebral body deformation (triangular or trapezoidal shape) are rare and usually found in the thoracic vertebrae.

Vertebral body osteomyelitis can be seen in the thoracolumbar spine in foals. Vertebral body fractures have been found in horses that have had severe trauma or falls. Complete or partial paraplegia results from damage to the spinal cord.

Prognosis

Grave.

Muscle Strain and Soreness

Damage to the muscles is the most common cause of back soreness in the horse. This most commonly involves the longis-simus dorsi muscle, which acts to extend and

laterally flex the vertebral column. All or part of the longissimus muscles usually is strained during ridden exercise, and

clinical signs are associated with altered performance and back pain of acute or chronic onset.

The principal sites of damage are the caudal withers and cranial lumbar regions (just in front of and behind the saddle area).

Most of these injuries respond to rest and physiotherapy, although several weeks may be needed for full recovery.

Lumbosacral Junction Abnormalities

Abnormal findings of the lumbosacral junction are often detected with ultrasonography. Findings:

Congenital abnormalities: lumbosacral ankylosis (sacralization of L6) or intervertebral ankylosis between L5 and L6

Disk degenerative lesions: fissuration or cavitation of the disk, dystrophic mineralization and ventral herniation

Intervertebral malalignment (spondylolisthesis) of the lumbosacral joint or the joint between L5 and L6

Intertransverse lumbosacral osteoarthrosis (periarticular osteophytes or remodeling can be seen on the joint margins).

Sacroiliac Joint Abnormalities

Acute and severe strain of the sacroiliac ligaments is associated with a history of injury and of severe pain in the pelvic or sacro-iliac region, often with marked hindlimb lameness.

Subacute or chronic sacroiliac strain and osteoarthrosis of the sacroiliac joint cause typical back soreness.

There is often a history of poor performance with an intermittent, often shifting, hindlimb lameness.

This may be associated with some restriction in hindlimb action and dragging of the toe of one or both hooves.

Diagnosis

Can be made in clinical practice with a combination of physical examination and ultrasonography.

Treatment and Management

Ultrasonographic-guided injections of steroids using cranial and caudal approaches to the joint

Mesotherapy over the painful area Rehabilitation using progressive warmup at a slow canter and exercises that develop

the gluteal muscles.

Tendinitis in Horses (Bowed tendon)

Inflammation of a tendon can be acute or chronic, with varying degrees of tendon fibril disruption. Tendinitis is most common in horses used at fast work, particularly racehorses.

The problem is seen in the flexor tendons and is more common in the forelimb than in the hindlimb.

In racehorses, the superficial flexor is involved most frequently.

Lesion

Primary lesion is central rupture of tendon fibers with associated hemorrhage and edema.

Etiology

Usually appears after fast exercise and is associated with overextension and poor conditioning, fatigue, poor racetrack conditions, and persistent training when inflammatory problems in the tendon already exist.

Predisposing Factor

Improper shoeing Poor conformation Poor training

Clinical Findings and Diagnosis

During the acute stage, the horse is severely lame and the involved structures are hot, painful, and swollen.

In chronic cases, there is fibrosis with thickening and adhesions in the peritendinous area.

The horse with chronic tendinitis may go sound while walking or trotting, but lameness may recur under hard work.

Diagnosis

Ultrasonography

Treatment

Best treated in the acute stage. The horse should be stall-rested, and the swelling and inflammation treated aggressively

with cold packs and systemic anti-inflammatory agents. Some degree of support or immobilization should be used, depending on the amount of

damage to the tendon. When a distinct hypoechoic or anechoic core lesion is present on ultrasound

examination, tendon splitting has been recommended (the rationale is to decrease intratendinous pressure due to serum or hemorrhage).

Shock wave therapy Intralesional injection of fat-derived stromal cells or cultured bone marrow-derived

mesenchymal stem cells, or autologous conditioned plasma. Rehabilitated using a regimen of increasing exercise. Superior check ligament desmotomy has been used as an adjunctive treatment to

minimize recurrence of the problem when the horse is returned to training. Superficial point firing Percutaneous tendon splitting. Annular ligament desmotomy is also used when tendinitis involves the area of the digital

tendon sheath.

Contraindication

Intratendinous corticosteroid injections

Prognosis

The prognosis for a flat-racing Thoroughbred racehorse to return to racing after a bowed tendon is guarded, regardless of treatment.

Developmental Orthopedic Disease

Developmental orthopedic diseases of horses constitute an important group of conditions that includes osteochondrosis, physeal dysplasia, acquired angular limb deformities, flexion deformities, and cuboidal bone malformations.

Osteochondrosis in Horses(Osteochondritis dissecans, Dyschondroplasia)

Osteochondrosis is one of the most important and prevalent developmental orthopedic diseases of horses.

Although its specific etiology is not known, it is considered to arise from a focal disturbance in endochondral ossification.

The term osteochondrosis is currently used to describe the clinical manifestation of the disorder.

The term dyschondroplasia is preferred when referring to early lesions because primary lesions are seen in cartilage.

The condition mainly affects articular growth cartilage, but the metaphysis may also be involved.

If the physeal metaphyseal cartilage is affected, bone contours and longitudinal growth are disturbed.

Involvement of articular cartilage at the periphery of joint surfaces leads to regressive changes at the joint margins, dissecting lesions, and the formation of cartilage flaps or osteochondral fragments (osteochondrosis).

Central articular lesions, because of weight-bearing effects, may lead to the development of subchondral cysts.

Axial skeletal involvement includes vertebral articular facets, which may be associated with stenosis of the vertebral canal and, therefore, ataxia and proprioceptive deficits but the relationship between these conditions is not clear.

Etiology

Osteochondrosis has a multifactorial etiology that includes rapid growth, overnutrition, mineral imbalance, and biomechanics.

Genetics has been implicated in some breeds.

Clinical Findings

In severe cases, other signs of developmental orthopedic disease also may be apparent. The most common presenting sign of osteochondrosis is a nonpainful distention of an

affected joint. First sign noted in foals is a tendency to spend more time lying down accompanied

frequently by joint swelling, stiffness, and difficulty keeping up with other animals.

An accompanying sign may be the development of upright conformation of the limbs, presumably as a result of rapid growth.

Fetlock osteochondrosis is particularly seen in younger foals below 6 months old. Lameness is usually absent or mild except for those sites mentioned above for which the

earlier sign of joint swelling is difficult to detect. In the stifle, some horses with subchondral bone cysts in the medial femoral condyle

present with lameness severe enough that a fracture may be suspected and swelling may only be detected on careful examination.

More severe signs are observed when osteochondral fragments come loose within the joint and are often seen in yearlings or older horses that present with stiffness, flexion responses, and varying degrees of lameness.

Diagnosis

Based on signalment and signs. Radiology Ultrasonography Arthroscopy – most accurate way to confirm diagnosis Scintigraphy - has limitations in growing horses due to normal high activity in physes and

sites of active endochondral ossification though useful for detecting subchondral cysts and secondary degenerative changes in older horses.

MRI - ideal for diagnosis of both early and late lesions Clinical pathology and the evaluation of synovial fluid is rarely helpful but can be used to

eliminate inflammatory causes of swollen joints.

Treatment and Management

Management of osteochondrosis depends on the site and severity of signs. Conservative treatment Particular care should be taken to ensure appropriate mineral supplementation Intra-articular medication with hyaluronic acid may be beneficial Injection of long-acting corticosteroids may help reduce swelling and improve any

associated synovitis but is not recommended in young, growing horses. Those cases considered for surgery are mainly treated arthroscopically. Damaged cartilage, osteochondral fragments, and compromised subchondral bone are

removed and the joint flushed extensively with sterile fluid.

Prognosis

Prognosis following removal of discrete osteochondral fragments is good. In cases with more extensive osteochondral damage, the prognosis depends on the

extent of the joint surface that must be removed. The prognosis is poor for cases with instability resulting from joint surface loss or in

which secondary osteo-arthritis (degenerative joint disease) is advanced. Cases involving subchondral cysts have a guarded prognosis as they are often in

important weightbearing areas of the joint and reconstruction of the joint surface is rarely possible.

Physitis in Horses(Epiphysitis, Physeal dysplasia, Dysplasia of thegrowth plate)

Physitis involves swelling around the growth plates of certain long bones in young horses and it can be a component of osteochondrosis.

Suggested causes include malnutrition, conformational defects, faulty hoof growth, excessive exercise, obesity, and toxicosis.

The condition is seen frequently in well-grown, fast-growing, heavy-topped foals during the summer when the ground is dry and hard, and on stud farmswhere the calcium:phosphorus ratio in the diet is imbalanced.

Physitis most commonly involves the distal extremities of the radius, tibia, third metacarpal or metatarsal bone, and the proximal aspect of the first phalanx.

It is characterized by flaring at the level of the growth plate, giving a typical “boxy” appearance to the affected joints.

Radiographs aid the clinical assessment. Microscopically, the physeal cartilage appears crushed and thinned, and new bone is

formed.

Treatment

Reducing food intake to reduce body weight or at least growth rate Confining exercise to a yard or a large, well-ventilated loose box with a soft surface Ensuring that the feet are carefully and frequently trimmed Correcting the diet if necessary.

Prevention

Older foal or yearling that is fat or heavy-topped should be watched carefully for clinical signs, especially when the ground is hard and dry.

Flexion Deformities in Horses(Contracted tendons, Club foot, Knuckling)

Flexor tendon disorders are associated with postural and foot changes, lameness, and debility.

They may be congenital and therefore identified in newborn foals or acquired at an older age. Uterine malposition, teratogenic insults (arthrogryposis), and genetic defects have been either implicated or proved to cause contracted limbs in newborn foals.

Chronic pain is the most common cause of acquired tendon contracture. Pain can arise from physitis, osteochondrosis, degenerative joint disease, pedal bone fracture, or soft-tissue wounds and infection.

Pain induces reflex muscle contraction with shortening of the flexor musculotendinous units.

The horse walks on its toes or knuckles in the fetlocks or occasionally the pastern joint.

Clinical Findings

Unable to stand Attempt to walk on the dorsum of their fetlocks Can stand but knuckle in the fetlocks or carpi In older foals, onset tends to be rapid may walk around on their toes with their heels off

the ground A slower onset is characterized by a “boxy” hoof with an elongated heel and concave toe Physitis frequently is evident in these horses Toe abscesses are a frequent complication of the hoof and locomotion changes, and

they add to the pain and deformity.

Treatment

Mild cases in newborn foals often require no treatment. More severe cases require supportive therapy, and it is essential to correct failure of

passive transfer of immunity if the foal has not been able to nurse adequately.

Use of splints necessitates careful fitting and management. Casts are generally safer if used only for short periods (5–7 days). High-dose oxytetracycline therapy is commonly used (40–60 mg/kg). Conservatively treatment with nutritional correction, proper hoof trimming, and analgesia. Desmotomy of the accessory ligament of the deep digital flexor tendon (inferior check

desmotomy) is the most successful and commonly used procedure for flexural eformity of the distal limb and does not interfere with future performance.

Superior check ligament desmotomy may be included for horses with fetlock deformities. For carpal deformities, sectioning of the tendons of insertion onto the ulnaris lateralis

and flexor carpi ulnaris is performed. In hindlimbs, tenotomy of the medial head of the deep digital flexor is performed, as the

inferior check ligament is often vestigial. In severe cases, tenotomy of the deep digital flexor tendon can be used as a salvage

procedure.

Nutritional correction, proper foot trimming, and analgesia are integral to recovery, even when surgery is indicated.

Prognosis

The prognosis is fair to good for horses that are diagnosed early and managed properly.

VM 175

EQUINE MEDICINE

Lameness in Horses

Submitted by: Davis Lumayna and Dwight Lee Baldo

Submitted to: Dr. Karen B. Gaerlan