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Published by the Florida Association of Equine Practitioners, an Equine-Exclusive Division of the Florida Veterinary Medical Association Issue 3 • 2014





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The President's Line

Suzan C. Oakley, DVM, Diplomate ABVP (Equine) - FAEP President


roviding world-class equine-exclusive continuing education has been our passion at FAEP for the past 10 years. When we graduated from vet school, most of us were told that 50% of what we knew would be obsolete or proven wrong in 5 years. It takes a lifelong commitment to “continual” education to be able to stay current and provide the best medicine possible, especially in this exciting age of ever-changing technology. Our meetings provide the opportunity to “keep up and catch up” with equine sports medicine, colleagues and friends in a great location. We hope to see you in beautiful Hilton Head, South Carolina from October 9-12, 2014, to celebrate the 10th anniversary of the FAEP Promoting Excellence Symposium. Our theme for the meeting is Achieving Peak Performance in the Equine Athlete. We have a special Saturday night celebration planned, featuring the always-entertaining Dr. Bo Brock; so join us to catch up with friends and share a good time. Our outstanding program includes the FAEP News Hour with Drs. Chris Kawcak, Rob MacKay and Margo Macpherson. Dr. Chris Pollitt will share his knowledge and research on laminitis with us in a 4-hour “Master Class” format. Many more top-of-the line speakers will weigh in on current issues in lameness, surgery, imaging, medicine and reproduction in the athletic horse. The Equine Sports Rehabilitation track features Drs. Duncan Peters and Rob van Wessum addressing the rehabilitation of equine tendon, ligament and spinal/pelvic injuries. Dr. Jen Skeesick PT, DPT, SCS will provide a human physical therapy perspective and Dr. Shelia Schils will discuss the development of equine rehabilitation protocols. Our goal for the entire meeting is to provide you with practical cutting-edge information that you can take home and use tomorrow. Don’t forget, the Ocala Equine Conference has moved to January 23rd -25th, 2015, in Ocala, Florida. We are excited to offer an ultrasound wet lab on Friday focusing on musculoskeletal, abdominal and thoracic imaging. Wet lab instructors will include Drs. Steeve Giguere presenting abdominal and thoracic ultrasound, and Rich Redding and Natasha Werpy on musculoskeletal ultrasound topics. Featured lecturers for the conference include Drs. Steeve Giguere, Eric Mueller, Rich Redding and Karen Wolfsdorf discussing foal respiratory disease, GI issues, lameness, imaging, and reproduction. Our Saturday night Keynote speaker will be Dr. Sue McDonnell, who will discuss the many facets of equine behavior. On Sunday, Dr. Ted Stashak will present an outstanding case-based seminar on wound management that will deliver practical, “take home and use tomorrow” information. We hope to see you soon at one of our meetings and welcome and encourage your contributions. Our meetings are tailored for you, so we need your input. Please consider contributing by volunteering for a committee or writing an article for The Practitioner. See you soon in Hilton Head or Ocala! Suzan


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SHOULDER INJURIES CAROL GILLIS, DVM, PhD, DACVSMR Shoulder Injuries “Shoulder function is a compromise between mobility and stability.1” The scapula of the horse is suspended from the trunk by ligamentous attachments and is the site of origin of the major muscles that both stabilize and move the forelimb. The scapula is able to slide both in the direction of the horse’s movement and dorso-ventrally during locomotion, which enhances the shoulder’s role as a shock absorber.2 A complex array of muscles, tendons, joint and bursas comprise the anatomy of the shoulder, and coordinate to allow it to function fully in the equine athlete. Injury to one or more structures leads to forelimb dysfunction.

History and Clinical Signs The biceps brachii tendon is the most commonly injured of the shoulder soft tissues due to its prominent location on the point of the shoulder. Unlike most tendons and ligaments, the biceps tendon is often injured as a result of direct trauma rather than cumulative overload. The history often includes the horse being kicked while breeding or being ridden, or hitting a fence or other solid object with the affected shoulder. Athletic use overload also occurs. Rarely, the biceps tendon is injured or bicipital synovitis develops secondarily to developmental or acquired orthopedic disease of the humeral tubercles.3 Synovitis of the bicipital bursa may occur alone or may be accompanied by damage to the biceps tendon. A horse with bicipital bursitis or biceps tendonitis will resent palpation of the tendon and pressure applied to the front of the shoulder. If the horse is asked to walk then halt, he often prefers to stand with the affected limb placed slightly caudal to the normal one in order to release tension on the tendon and compression of the bursa. The supraspinatus and especially the infraspinatus tendons of insertion assume the role of lateral collateral ligaments for the shoulder joint, which is lacking these structures. The supraspinatus muscle tendinous insertion is divided into medial and lateral lobes which insert on the cranial aspects of the medial and lateral humeral tubercles, straddling the biceps tendon. Due to their prominent placement on the humeral tubercles, the supraspinatus insertions, particularly the lateral lobe, are prone to the same injuries as the biceps tendon; therefore, injury to the supraspinatus should be suspected based on the same injury history. Clinical signs are similar to those for the biceps tendon. The infraspinatus muscle’s tendon of insertion traverses the lateral aspect of the shoulder joint before dividing into superficial and deep components. The short, deep tendon inserts on the caudal edge of the greater tubercle. The superficial, long tendon crosses the humeral tubercle to insert on the dorso-lateral aspect of the humerus. A bursa lies between the long tendon and the caudal eminence of the greater tubercle. The infraspinatus tendon and/ or its bursa are often injured when the lower limb is abruptly or excessively adducted; for instance, when a western event horse or a polo pony suddenly changes direction while travelling at high speed. Pain on palpation of the muscle/tendon and on limb adduction/ 8  The Practitioner 

abduction are common clinical signs. The deltoideus muscle is a primary flexor of the shoulder joint. It is fairly well protected from direct trauma due to its caudo-lateral location and is not often injured due to overuse. It is most commonly injured in conjunction with humeral deltoid tuberosity fractures, as this is its site of insertion along with the superficial pectoral muscle and the brachiocephalicus muscle. Horses with deltoid tuberosity fractures are usually Grade IV-V/V lame and often have an open wound or marked swelling from a kick or blow to the area.4 Lameness associated with the scapula or humerus is uncommon in the adult horse, and is often associated with a fall or direct blow resulting in acute symptoms. In young equine athletes, stress fractures of the scapula and developmental orthopedic disease manifestations are more common. Stress fractures generally cause an acute lameness of brief duration.5 Developmental orthopedic disease results in chronic, increasing lameness. Osseous cystlike lesions of the humeral tubercles are rare; they apparently occur subsequent to repetitive bone trauma. Occasionally, fractures of the proximal humerus occur and are sometimes associated with luxation or severe damage to the biceps tendon. Lameness associated with large fractures is generally acute and significant. The horse will resent palpation/manipulation of the affected structure; however, swelling may be difficult to detect due to overlying heavy musculature. Pain should be localized to the shoulder region using a careful clinical exam, including diagnostic nerve blocks of the distal limb if needed, as acute distal limb lameness, for example from a severe foot abscess, may cause reluctance to bear weight and trembling, and flaccid shoulder musculature which may sometimes be mistaken for a shoulder region injury.

Diagnostic Imaging The primary imaging modality for diagnosis of muscle, tendon and bursa injuries is ultrasonography. A high frequency linear transducer (7-14 MHz) is ideal for the examination. The shoulder area should be clipped except for very short-haired horses, and washed with mild soap and water followed by application of ultrasound gel. The tendinous origin of the bicipital muscle is located on the cranial/distal aspect of the distal scapula, therefore it is important to begin the exam at this location. Figure 1A shows long axis and short axis views of a normal biceps tendon at origin. Note the strong parallel linear fiber pattern and evenly bright echogenicity of the tendon. Issue 3 • 2014

Also, note the hypoechoic deep portion of the biceps tendon; this represents the fibrocartilagenous tissue that is a result of compression as the tendon glides over the humeral tubercles. The bony contour of the humeral tubercles is smooth, bright and regular, indicating normal bone surface.



Figure 1B shows long and short axis views of an injured biceps tendon at origin. Note the significant gaps in the fiber pattern, the enlargement of the tendon in cross-sectional area, and the multiple small core lesions. The tendon is evaluated in long and short axis planes as it traverses the humeral tubercles and joins the muscular portion distally. At the level of the humeral tubercles, the most common site of injury, the tendon is bilobed; each lobe may need to be Lateral Medial evaluated separately due to size. The usual ultrasonographic Figure 3 shows a short axis view of the lateral lobe of parameters of size, echogenicity and fiber pattern should be used a biceps tendon with healed tendonitis (note the white to determine if injury is present. The deep edge of the tendon is arrow pointing to a small area of scar tissue). There is hypoechoic normally, as it undergoes compression by the humeral synovial proliferation within the bursa. The lateral surface tubercles and responds by having a fibrocartilagenous component, of the intermediate humeral tubercle is irregular secondary creating two diagnostic challenges. The first is to determine if to trauma that occurred at the same time as the initial the hypoechoic region is normal, either through practice in use tendon injury. of ultrasound or by comparison with the opposite tendon. The second is to differentiate the hypoechoic tendon from the fluid The bursa may be accessed under ultrasound guidance using a contents of the bicipital bursa and the thin layer of cartilage that covers the humeral tubercles in the adult horse. This can best be 1 ½” 19 ga. needle to enter either the shallow part of the sheath achieved by changing the transducer angle slightly until the bursa lateral to midline or the lateral part of the bursa between the lateral lobe of the biceps tendon and the axial border of the cranial sheath can be detected. The bursa normally contains less than 3 mm depth of greater humeral tubercle. Fluid can usually be aspirated from a hypoechoic to anechoic fluid. With inflammation, the bursa distended sheath for evaluation. Infusion with 15-20 ml of local initially distends with effusion, then synovial proliferation, and anesthetic can be used to confirm that the bursa is the source of pain. A recent study6 has confirmed that ultrasound guidance finally adhesions develop over time without treatment. improves the accuracy of injection into the bicipital bursa, infraspinatus bursa and scapulo-humeral joint significantly; 14/24 attempts were successful “blind” and 24/24 attempts were successful using ultrasound guidance. In a small percentage of horses (less than 20% of horses), the bursa communicates with the shoulder joint, therefore response to anesthesia must be interpreted in conjunction with ultrasonographic findings in order to differentiate which structure is affected. Distal to the humeral tubercles, the muscular portion of the biceps tendon is examined in both planes, to its short tendinous insertion on the radial tuberosity and its long tendon (Lacertus fibrosus), which blends with the extensor carpi radialis and forearm fascia. The supraspinatus muscle is examined in short and long axis views, from its origin in the supraspinous fossa to its tendinous Lateral Medial insertions medial and lateral to the biceps tendon on the humeral Figure 2 shows a normal short axis view of the lateral lobe tubercles. The infraspinatus muscle is examined from its origin of the biceps tendon and its surrounding bursa. Note that in the infraspinous fossa to its tendinous deep (short) and the bursa, which is more accurately termed a sheath, extends shallow (long) insertions on the lateral aspect of the humerus. shallow to the tendon as well as deep to it, attaching only at The Infraspinous bursa is evaluated for the amount and character dorsal midline. Bursal fluid depth on all three measurements of fluid. Some normal infraspinatus bursas may be difficult to is within normal limits. visualize.7 

The Practitioner  9 

Figure 4 shows a long axis view of an infraspinatus bursa that is distended with hypoechoic fluid and fibrin following recent trauma. Deltoideus muscle damage and humeral deltoid tuberosity fracture fragments can be identified ultrasonographically. A cranio45o medial-caudo-lateral radiographic view will also accurately detect the fracture.4 Any open wound in the shoulder area should be an indication for ultrasonographic evaluation of the associated soft and hard tissues. Air or gas in the wound can make it difficult to obtain diagnostic ultrasound images; therefore, ultrasound should be performed after cleaning but prior to probing the wound. Foreign bodies and loose bone fragments can be removed using ultrasound guidance. Drainage can be established for deep, walled-off fluid pockets containing serum or purulent material. The extent of soft tissue damage can be documented so that future healing progress can be assessed. Diagnostic ultrasound is useful to image bony lesions that extend to the surface, such as fractures of the scapular spine and of the deltoid tuberosity. A displaced fracture is seen as a strongly hyperechoic structure, casting an acoustic shadow that is distracted from the parent bone, resulting in a stair step appearance. Irregular bone contour around the fracture line may be indicative of callus formation.4 Communicating cystlike lesions of the humeral tubercles are readily seen on ultrasound examination. Ultrasound is also useful to examine the lateral aspect of the articular surface of the humeral head, particularly of the caudal surface which is a very common site for developmental orthopedic disease lesions.8 Special radiographic views, including flexed skyline view and oblique views of the humeral tubercles, may be helpful in evaluating bony lesions of the shoulder joint.9 Nuclear scintigraphy and MRI are also indicated to define deeper bone lesions, although the use of MRI is limited in adults due to the size of the shoulder region.

Treatment and Rehabilitation Bicipital or infraspinatus bursa inflammation without concomitant muscle/tendon injury is treated with systemic NSAID administration, ultrasound-guided injection of polysulfated glycosaminoglycan, steroid or steroid and hyaluronic acid, cold therapy for 15 minutes twice daily, and walking exercise for 4 days. The horse should be re-evaluated prior to return to work to ensure effectiveness of therapy. Infectious bursitis is treated with lavage, appropriate antibiotics and 10  The Practitioner 

anti-inflammatory therapy. It is important to treat bursal inflammation in conjunction with infection aggressively, otherwise synovial proliferation and adhesions may cause longterm lameness and loss of normal tendon gliding long after infection has resolved. Injury to the tendinous portion of the biceps, supraspinatus or infraspinatus is treated initially with anti-inflammatory therapy, either systemic NSAID at an appropriate dose for 3 weeks or with topical application of 1% diclofenac cream twice daily for 3 weeks prior to exercise. Oral methocarbamol for 3 weeks is also helpful to relieve muscle spasm and pain. Physical therapy, including massage and cold therapy for 15 minutes twice daily after exercise for 3 weeks will assist in mobilizing edema and in pain relief. Extracorporeal shock wave therapy, laser, therapeutic ultrasound, acupuncture and myofascial release have also been used to provide pain relief. Controlled exercise is the essential requirement for healing. Pasture turnout yields a 25% or less chance for return to work without re-injury as the horse exercises randomly and intermittently, resulting in partial healing followed by re-injury, in a cycle that can continue for years. Therefore, the horse should be confined to an area in which he only walks, generally a 12’ by 24’ area maximum. Controlled exercise is initiated immediately with 15 minutes of hand walking twice daily; this is increased by 5 daily minutes every 2 weeks. The horse is re-examined clinically, and using diagnostic ultrasound every 6-8 weeks depending on the initial severity of the lesion, with mild lesions requiring shorter time intervals between examinations and potential increase in exercise level. At the first recheck exam, the horse should be pain free on examination at the walk and on shoulder palpation/manipulation. Ultrasonographic findings are evaluated as good, fair or poor. Good healing progress includes resolution of swelling, decrease in size of any discrete core lesion and improvement in overall echogenicity for generalized tears or increase in echogenicity of discrete core lesions. Good or fair progress indicates that the tendon has healed sufficiently for riding exercise at the walk to begin. The horse remains confined in an area in which he only walks except for riding exercise and a second daily exercise period of hand walking for 15-20 minutes. On average, riding time begins at 25 minutes and increases every 2 weeks. Poor tendon healing indicates either inappropriate rehabilitation due to owner or horse non-compliance or pain/lameness elsewhere, resulting on overload strain of the damaged shoulder tissues; these complicating factors need to be identified and corrected for normal healing to proceed. At the second recheck examination, the horse should be pain free on examination at the walk and trot, and on shoulder palpation/manipulation. Good healing progress includes resolution of any discrete core lesion or improvement in overall echogenicity, stable cross-sectional area and stable or slightly improved fiber pattern. Good or fair progress indicates sufficient healing for trot exercise to begin 5 days per week. Amount of trot work varies with age and intended use of the horse, but in general is initiated as a 5-minute set after a 20-minute walk warm-up 5 days per week. Giving detailed instructions for the rider to exercise the horse at varying pace and collection, and to perform easy lateral work maneuvers such as 20-meter circles and serpentines and walk-to-halt transitions, will help the horse Issue 3 • 2014

to maintain or improve flexibility and encourage the damaged tissues to heal. Additional 5-minute trot sets are added at 2-3week intervals. The horse remains confined in an area in which he only walks, except for riding exercise and a second exercise period of hand walking for 20 minutes minimum. At the third recheck examination, the horse should be clinically sound and pain free on palpation/manipulation. Good healing progress on ultrasound examination includes stable cross-sectional area, good echogenicity and improving fiber pattern. Increase in cross-sectional area of greater than 12% is an indication of overload of the healing tendon either from inappropriate rehabilitation, including excessive controlled or uncontrolled exercise, or pain/lameness elsewhere. These factors must be identified and corrected at this time for a successful outcome. Good or fair progress indicates that sufficient healing has occurred for canter to be added to the current exercise schedule 5 days per week. Work is increasingly adjusted to the horse’s future job; generally, canter is added in 5-minute sets in the same manner that trot was added. After one week of canter, the horse can be turned out. At the fourth recheck examination, the horse should be clinically sound and pain free on palpation/manipulation, with a similar range of motion to the opposite (uninjured) limb. Good healing progress on ultrasound examination includes stable, normal cross-sectional area, normal echogenicity and parallel linear fiber pattern; in other words, essentially complete healing. (If the area is examined further periodically, minor improvements in fiber pattern will be seen along with stable cross-sectional area and stable echogenicity.) Good healing indicates that the horse is ready at this time to begin 4-6 weeks of training for his sport, followed by return to competition.9 Muscle injuries are less common than injury to the tendinous portion. If a muscle injury is diagnosed, a similar treatment and rehabilitation program is initiated; however muscle heals much more rapidly than tendon, therefore each exercise level is generally maintained for a 4-week interval prior to a clinical and ultrasound re-examination rather than 6-8 weeks. Wounds ranging from punctures to open laceration in the shoulder region, should be treated with removal of any bone fragments or foreign bodies under ultrasound guidance, followed by debridement of contaminated tissue, lavage and appropriate antibiotic therapy. Healing of damaged muscle or tendon is monitored using ultrasound. Stress fractures of the scapula respond well to rest and confinement, requiring about 4 months to heal as seen on ultrasound. A careful training program prior to return to competition is required to allow the horse, as well as the scapula, to return to full strength. Fractures of the scapular spine are often associated with wounds; removal of fragments is usually necessary for wound healing to proceed. Full thickness scapular fractures in longitudinal or transverse configuration are uncommon, however, there are several reports of internal fixation followed by several months of rest. Treatment of deltoid tuberosity fractures and concomitant deltoideus muscle injury requires wound care, rest and rehabilitation of the muscle injury. Cystlike lesions of the humeral tubercles respond well to treatment of the associated bursitis, and if tendon damage is also present, the controlled exercise program outlined in the soft tissue section. 

Prognosis The percentage of horses that return from shoulder tendon injuries to intended use without re-injury is approximately 85% if a controlled exercise protocol is successfully completed. Muscle and tendon possess intrinsic stem cells which will repair damaged tissue, provided that an appropriate environment for healing, i.e. initial ant-inflammatory therapy followed by stimulation through a correct level of loading, is provided. The author has seen no difference in horses following such a protocol alone and horses in which regenerative therapy has been employed. This may be due in part to our limited, although increasing, knowledge of the appropriate cells or cellular products to use and how to employ them; however little improvement over the current good prognosis may be difficult to obtain. Conversely, regenerative therapy without a controlled exercise program of the same duration yields results in a 25-45% range for return to work without re-injury. Fractures of the scapular spine have a good prognosis for return to athletic use after several months of rest, followed by increasing exercise.5 Fractures of the deltoid tuberosity also have a good prognosis for return to athletic use. Cystlike lesions of the humeral tubercles have a good prognosis for return to athletic use. Fractures of the humeral tubercles,11 humeral head, or the neck of the scapula have a variable prognosis for return to athletic use depending on location and configuration; these fractures may lead to loss of limb stability and subsequent development of arthritis of the shoulder joint. Developmental orthopedic disease lesions of the articular surfaces of the humeral head and scapula have a fair to guarded prognosis to return to athletic use depending on the type of athletic endeavor. Approximately 67% of nonracing horses and 14% of race horses were able to eventually engage in their intended use. Horses treated with arthroscopic debridement failed to have a better outcome than conservatively managed horses.12

Discussion The shoulder region of the equine athlete is a sometimes overlooked, complex, and important location for lameness from soft and hard tissue injury or disease. Ultrasound is extremely helpful in the diagnosis and treatment of soft tissue and many bone injuries. In general, soft tissue injuries heal well given appropriate treatment and time, as do many small bony lesions. Major bone disruptions have a variable outcome due to loss of shoulder stability and mobility.


1. Veeger HE, Van der Helm FC. Shoulder function: The perfect compromise between mobility and stability. J of Biomechanics 40 (2007) 2119–2129. 2. Lawson SE, Marlin DJ. Preliminary report into the function of the shoulder using a novel imaging and motion capture approach. Eq Vet J Suppl. 2010 Nov;(38):552-5. 3. Little D, Redding WR, Gerard MP. Osseous cyst-like lesions of the lateral intertubercular groove of the proximal humerus: A report of 5 cases. Equine Vet Ed 2009 Feb;21(2):60–66.

The Practitioner  11

4. Fiske-Jackson AR, Crawford AL, Archer RM, Bolt DM, Smith RK. Diagnosis, management, and outcome in 19 horses with deltoid tuberosity fractures. Vet Surg. 2010 Dec;39(8):1005-10. 5. Davidson EJ, Martin BB Jr. Stress fracture of the scapula in two horses. Vet Radiol Ultrasound. 2004 Sep-Oct;45(5):407-10. 6. Schneeweiss W, Puggioni A, David F. Comparison of ultrasoundguided vs. 'blind' techniques for intra-synovial injections of the shoulder area in horses: Scapulohumeral joint, bicipital and infraspinatus bursae. Equine Vet J. 2012 Nov;44(6):674-8. 7. Whitcomb MB, le Jeune SS, Macdonald MM, Galuppo LD, Judy CE. Disorders of the infraspinatus tendon and bursa in three horses. J Am Vet Med Assoc. 2006 Aug 15;229(4):549-56 8. Redding WR, Pease AP. Imaging of the shoulder. Equine Vet Ed. 2010 Apr:199-209. 9. Gillis CL. Soft tissue injuries. In Hinchcliff KW, Kaneps AJ eds. Equine Sports Medicine and Surgery 2nd Ed 2014: 399-419.St Louis: Elsevier. 10. Jenner F, Ross MW, Martin BB, Richardson DW. Scapulohumeral osteochondrosis. A retrospective study of 32 horses. Vet Comp Orthop Traumatol. 2008;21(5):406-12. 11. Mez JC, Dabareiner RM, Cole RC, et al. Fractures of the greater tubercle of the humerus in horses: 15 cases (1986–2004). J Am Vet Med Assoc 2007;230:1350–1355. 12. Jenner F, Ross MW, Martin BB, Richardson DW. Scapulohumeral osteochondrosis. A retrospective study of 32 horses. Vet Comp Orthop Traumatol. 2008;21(5):406-12.

Carol Gillis, DVM, PhD, DACVSMR Dr. Carol Gillis is a graduate of UC Davis School of Veterinary Medicine. She was the owner of a sport horse practice for 8 years during which she became one of the first equine practitioners to perform ultrasound examinations on the musculoskeletal system of horses. Dr. Gillis returned for an equine surgery residency at UC Davis. Following completion of the residency, she obtained a PhD in equine tendon and ligament pathophysiology. Concurrently she established the equine ultrasound service at UC Davis, pioneering ultrasound of the musculoskeletal system at the University, and developing courses and wet labs to train veterinary students, residents and veterinarians how to perform and interpret ultrasonographic examinations. Dr. Gillis developed many ultrasound protocols for previously unexamined sites on the horse. She has performed more than 22,000 equine diagnostic ultrasound examinations and rehabilitation guidance for problems identified. She has authored more than 50 scientific publications in journals, including the American Journal of Veterinary Research and the Journal of the American Veterinary Medical Association. Dr. Gillis operates a referral Ultrasound and Sports Medicine practice in Aiken, South Carolina, and is a charter member and Diplomate of the American College of Veterinary Sports Medicine and Rehabilitation.

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The Practitioner  13

















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Management of Hoof Wall Defects: Quarter Cracks and Toe Cracks R.Scott Pleasant, DVM, MS, DACVS; Travis Burns, CJF, TE, AWCF Introduction

(affected by load, limb conformation and foot care). During the stance phase of the stride, the hoof deforms under the weight of the horse and the dynamic loads of locomotion. The oblique, truncated, incomplete cone shape and decrease in wall thickness from the toe to heels in the well-shaped hoof, causes the toe of the wall to bow backwards and the quarters and heels to flare at the ground surface (spread horizontally) during loading. This pattern of deformation appears to be an extremely efficient mechanism for dampening and distributing the loads of weight bearing and locomotion. Changes in hoof capsule shape away from this ideal may negatively affect its mechanical behavior and predispose it to injury.

Pathophysiology of Quarter Cracks and Toe Cracks The equine hoof capsule serves to support and protect the internal structures of the foot. Conditions which result in the loss of the structural integrity of the hoof capsule such as full thickness quarter cracks and toe cracks (full thickness hoof wall fractures) are not uncommon and may result in lameness. Once the hoof wall has been fractured, the healing process is primarily replacement by growth. New growth originates from the coronet, and depending on the region of the crack, it may take 4-12 months for the damaged hoof wall to be replaced. In most cases, healing by replacement occurs uneventfully if the underlying cause(s) of the crack is addressed and the horse is allowed appropriate rest. Management of the underlying cause(s) is paramount in reducing the likelihood of recurrence of performance-limiting cracks. Frequently, veterinarians and farriers encounter situations where it is important for horses with full-thickness quarter cracks or toe cracks to remain in work. These situations require the use of techniques that not only address the underlying cause(s), but also stabilize the injured tissues when necessary. The purpose of this presentation is to discuss the predisposing factors for full thickness quarter and toe cracks and to provide strategies for managing these hoof wall defects.

Many causes for full-thickness quarter cracks and toe cracks have been described, including coronet injuries, inappropriate farrier practices, poor quality hoof walls (as a result of genetics, nutrition, and/or environment), White Line Disease, and hoof capsule distortion. In these authors' experience, the most common underlying cause of full-thickness quarter cracks and toe cracks is hoof capsule distortion. It is well accepted that the hoof capsule adapts and changes shape according to how it is loaded. Hoof wall growth tends to be slower where the majority of weight is borne and faster where the least amount of weight is borne. Faulty limb conformation adversely affects how the hoof is loaded, and habitual disproportionate loading will change the shape of the hoof capsule over time. The resulting distortion of the hoof may negatively affect its mechanical behavior, resulting in abnormal stress and strain within its tissues. If the changes in stress and strain become excessive, the hoof wall will be predisposed to injuries such as full-thickness quarter cracks and toe cracks. Stress and strain to the hoof wall may become excessive in a

Relevant Anatomy and Biomechanics The equine hoof capsule is composed of the hoof wall, sole, frog and bulbs of the heel. The hoof capsule is made predominately of keratinized epidermal cells and forms a tough, obliquely oriented, truncated, incomplete cone that is folded in on itself on each side at the heels. The hoof wall is typically thickest in the toe region, and becomes thinner and more elastic toward the heels. The medial hoof wall is usually straighter (less angled) and more upright (steeper) than the lateral hoof wall. The mechanical behavior of the hoof capsule depends primarily on the physical properties of the materials that make it up (affected by nutrition and hydration) and on its shape 

The Practitioner  15 

variety of clinical situations. Stress and strain may become excessive in horses with relatively minor hoof capsule distortion, but who experience high loads on their hooves (e.g., heavy use or work on hard ground), or in horses with marked hoof capsule distortion but who experience relatively normal loads on their hooves. In either situation, the underlying concept is that there is an imbalance between the load applied and the hoof wall’s capacity to withstand that load. If hoof wall stress/strain is excessive or repetitive, a full thickness hoof wall crack may result. It is important for veterinarians and farriers to recognize the cause and effect of hoof capsule distortion. Limb conformation directly affects hoof capsule loading, which affects hoof wall shape. For example, in horses with base wide conformation, the medial heel quarter bears the most weight. This may cause the wall in this area to grow slower and become more vertical. If not managed properly, the medial heel quarter may eventually become displaced axial to the coronet (“roll under”) and the coronet at the heel may displace proximally, assuming a “sheared heel” conformation. As a result of the disproportionate load, the lateral heel quarter grows relatively faster than the medial heel quarter causing a distortion that can be compounded over time. The resulting hoof distortion negatively affects the mechanical behavior of the hoof wall causing the medial heel quarter to bend axially at the ground surface and bow outward at the coronet during loading, predisposing to a full thickness wall crack in the medial quarter region that originates at the coronet and extends distally some distance (a “quarter crack”). On close examination, quarter cracks usually “open” at the coronet when the foot is loaded and “close” when the foot is unloaded. The resulting full thickness wall crack usually results in performance limiting lameness. In horses with base narrow conformation, the opposite occurs. The lateral heel quarter bears the most weight, tends to grow slower, and become more vertical. The lateral heel quarter may eventually “roll under” and the coronet on the lateral side may displace proximally. The resulting hoof wall distortion may result in abnormal bending of the lateral hoof wall that predisposes to lateral quarter crack formation. Full-thickness toe cracks are commonly seen in horses with long toe, low heel conformation. This conformation loads the heels of the foot excessively, limiting growth at the heels and causing relatively faster growth at the toe. This increased toe length creates excessive leverage on the hoof wall in the toe region during loading and especially at breakover during the stance phase of the stride, predisposing to crack formation. Full-thickness toe cracks associated with this type of conformation usually begin as minor, incomplete cracks at the ground surface of the foot. If neglected, the cracks may propagate deeper and up the hoof wall, and extend to the coronet. Lameness results if the crack “fractures” completely through the hoof wall, creating instability of the foot. It is not uncommon for toe cracks of this origin to be complicated by secondary White Line Disease. Full-thickness quarter and toe cracks occur almost exclusively in the front feet, presumably because the front feet bear more weight than the hind feet.

Management of Quarter Cracks Management of full-thickness quarter cracks involves identification and correction/management of balance issues 16  The Practitioner 

and coronet displacement issues, unloading the injured region, stabilization of the hoof wall, and committed follow up. In all cases, every effort should be made to identify the cause(s) of the crack; if not, the success of treatment will be limited and the crack will likely reoccur. Assessment should begin with evaluation of the horse’s limb and hoof conformation, noting any cause and effect of limb conformation on hoof loading and hoof capsule conformation/ distortion that would predispose to crack formation. Base wide and base narrow conformation should be evaluated, and if present, the effects on hoof capsule loading and shape noted. The presence of excessively vertical heel quarters, “rolled under” heel quarters, and displaced coronets on the overloaded side of the hoof should be determined. A focal “prominence” of coronet displacement is often present just above the origin of the crack, indicating the point of maximal abnormal stress/ strain. 0o horizontal dorsopalmar and lateromedial radiographs centered on the solar margin of the distal phalanx can be helpful in evaluating hoof capsule/distal phalanx alignment. In horses with quarter cracks, there may be inappropriate medial to lateral orientation of the distal phalanx relative to the ground. If medial to lateral imbalance of the distal phalanx is present, it may match the coronet displacement (i.e., the distal phalanx tilts in the same plane as the coronet displacement) or be opposite of the coronet displacement (i.e., the distal phalanx tilts in the opposite plane of the coronet displacement). Cases where the distal phalanx imbalance is opposite of the coronary band displacement are likely the result of disproportionate loading on one side of the hoof, causing relatively faster hoof growth on the side of the foot where the least amount of weight is borne, and slower growth on the side where the most weight is borne. Affected feet should be trimmed appropriately, using the guidelines of a parallel hoofpastern axis, with the center of articulation bisecting the weight bearing surface of the foot, and the heels of the hoof capsule extending to the base of the frog. If medial to lateral imbalance is present, the feet should also be trimmed in an attempt to realign the solar margin of the distal phalanx parallel to the ground. The amount of correction that is possible at any given trimming is dictated by the amount of sole depth available. It is acknowledged that complete correction of medial to lateral imbalances is rarely possible and that the imbalances tend to reoccur between trimming cycles. However, the practice of always attempting to correct the imbalances will help correct and limit hoof wall distortion. It is critical that uneven growth/imbalances are not ignored for successful longterm management. The fit of the shoe can be used to help improve Issue 3 • 2014

the foot’s platform. For example, in quarter crack cases where should be treated with a topical disinfect/drying agent such as the medial or lateral hoof wall is excessively straight or “rolls 2% Tincture of Iodine or Thrush Buster (Delta Mustad Hoofcare, under,” the corresponding branch of the shoe should be fit as Lake Forest, MN) at least once daily. full as practical to provide appropriate symmetry to the ground If a horse with a full-thickness quarter crack is being taken surface of the foot. out of work, the crack will not be repaired during the initial Correction/management of soft tissue displacements farriery. When the horse is presented for a subsequent reset, (proximally displaced coronets), if present, is accomplished by there should be significant new solid growth at the coronet above unloading or “floating” the displaced region. The specific farriery the defect. This would indicate that the initial farriery is effective method utilized usually depends on personal preference. One in unloading the affected heel quarter. At this time, the crack can method is to shoe the affected foot with a properly fit shoe with be repaired or allowed to grow out. a rim pad (plastic or leather), minus the area of the pad that Ideally, horses with full-thickness quarter cracks should be would contact the affected quarter and heel. This results in the taken out of work and allowed time for inflammation to resolve, region of the hoof with the displaced coronet being suspended the dermal portions of the crack to heal, existing hoof distortions (“floated”) approximately 1/8–1/4 inch above the shoe. This and soft tissue displacements to be corrected/improved, and allows for correction/improvement (“settling”) of the soft the cracks to begin to be replaced by new wall before they are tissue displacement and also minimizes the external loads on repaired. However, veterinarians and farriers often encounter the injured area. The gap between the shoe and the foot is filled situations where it is important for horses with full-thickness with a small piece of weather stripping to prevent dirt/debris quarter cracks to continue to train and compete. In these cases, from accumulating in the “floated” region. The solar surface of the repair/stabilization of the crack is often necessary before hoof foot is filled with a liquid urethane hoof packing material (Equi- distortions and soft tissue displacements can be corrected, and Pak, Vettec Hoof Care Products, Oxnard, CA) to help support the sometimes before the dermal portions of the crack have healed/ digit and minimize internal stresses on the crack. The urethane dried out sufficiently. Several techniques exist for repairing and material is applied to ground level everywhere except in the allowing continued treatment of the crack in these cases. Fully region of the affected heel/quarter where it is only applied to addressing the hoof distortion and soft tissue displacement shoe level. Applying the hoof packing in this manner maintains issues should be emphasized as soon as the horse is able to be the “float” of the affected heel/quarter region. taken out of work. A second method involves a “double trimming” technique (Dr. Our preferred technique for repairing quarter cracks is to Steve O’Grady). The affected foot is first trimmed appropriately “plate” the crack with a composite of polymethylmethacrylate as described above, and then before attaching the shoe, a second adhesive (Equilox, Equilox International, Pine Island, MN) trim is performed under the proximally displaced quarter/heel. and a polymeric fabric. Before plating the crack, the hoof wall The second trim begins at the ipsilateral toe and increases in must be prepared to accept the adhesive (cleaned/sanded) and depth toward the heel. The amount of heel that can be taken an antiseptic packing applied into the crack bed to prevent off in the second trim depends on the sole depth in the quarter/ adhesive from entering the crack. The type and number of heel area. Ideally, the amount of heel removed corresponds to layers of fabric used to construct the plate will depend on the amount of proximal displacement of the coronet. The foot the anticipated strength needed. For most cracks, 3 layers of is then shod with asymmetrically fitted wide web steel straight polymethylmethacrylate saturated polyester/vectran fabric bar shoe, creating a space that resembles a wedge between the (Sound Horse Technologies, Unionville, PA) provide sufficient affected quarter/heel and the shoe. If there is not enough sole strength. The plate should extend from the coronet to the distal depth under the affected heel for the second trim, the wall can be surface of the hoof wall and at least 1.5 inches dorsal and palmar raised with a full leather pad. When a full pad is used, impression from the edges of the crack. Each side of the polyester/vectran material (Equilox Pink, Equilox International, Pine Island, MN) is fabric is saturated with adhesive. The layers are then stacked and placed beneath the pad to fill the frog sulci in the palmar section of the foot from the apex of the frog palmarly, except under the displaced heel. A third potential method that is used commonly on racehorses (Ian McKinlay) for floating the affected quarter/ heel region is to trim the affected foot appropriately, and then use a shoe that has a two component polyurethane rim pad affixed to it (Yasha Shoe, Tenderhoof Solutions, Ontario, Canada). The polyurethane in the heel area of the shoe is significantly softer than the polyurethane covering the rest of the shoe, and therefore functionally unloads and “floats” the affected heel. The crack defect should be debrided/explored with a motorized grinding tool and/or hoof knife, removing obviously undermined and diseased hoof wall. Exploration often reveals wall damage and undermining that exceeds initial visual appreciation. Care should be taken not to traumatize the dermis during debridement. No hemorrhage or only occasional pinpoint hemorrhage should occur during debridement. After debridement, the crack defect 

The Practitioner  17 

pressed together with a roller in order to expel excess adhesive. The plate is applied and allowed to cure with the foot unloaded so that the crack is stabilized in a “neutral” position. Small holes may be drilled proximally and distally through the repair into the crack defect in order to “vent” the crack and/or to allow continued treatment beneath the repair. The repair should be completely removed and reapplied (from the distal wall to the coronet) at least every other shoeing in order to minimize localized stress at the top of the repair. Complete reconstruction of the crack (filling the crack bed with adhesive as well as plating over the defect) may eventually be performed, but only after the crack bed is completely dry. In many horses, a residual defect will remain apparent after the crack has grown out. This is manifested by a “faint line” and/or a slight “inversion” of the wall in the area of the previous crack. This may represent permanent injury to the germinal tissues of the hoof wall as a result of the original crack. In these cases, it is recommended to maintain the horse with a polymethylmethacrylate/polymeric fabric plate over the affected area whenever the horse is in training in order to reduce the risk of repeated cracks.

Management of Toe Cracks

in horses with this type of conformation begins with trimming the feet using the guidelines outlined above. The dorsal surface of the hoof wall should be dressed back to align with the dorsal surface of the distal phalanx. The feet should be shod with some form of enhanced breakover to reduce leverage on the toe. The shoes should also be fit to provide as much palmar support as practical to improve the foot’s base of support and to encourage more appropriate hoof growth. Stabilization of toe cracks can be accomplished via several techniques. Our preferred technique is to stabilize toe cracks with polymethylmethacrylate adhesive saturated polymeric fabric “plates” using the same technique and principles as described for quarter crack repair. It is extremely important to attach the plate with the foot off the ground or in the unloaded position. This ensures that the defect is affixed in the open position allowing better alignment and reducing any compression on the dermal papillae producing horn tubules. Further stabilization of the foot (minimizing internal movement of the digit) is achieved by use of a support shoe (Heart Bar shoe or Heel Plate shoe with impression material) and/or via polyurethane sole support materials (EquiPak, Vettec Hoof Care Products, Oxnard, CA).

In horses with toe cracks associated with long toe, low heel conformation, radiographic evaluation often displays divergence of the distal dorsal hoof wall from the dorsal surface of the distal phalanx, excessive digital break-over, and a flat to negative distal phalanx palmar angle. Management of full thickness toe cracks

Strength since 1962

Robert Scott Pleasant, DVM, MS, DACVS Dr. Scott Pleasant is an Associate Professor in the Department of Large Animal Clinical Sciences at the Virginia - Maryland Regional College of Veterinary Medicine (VMRCVM), Virginia Tech. Dr. Pleasant has been a faculty member at the VMRCVM since 1991. He is board certified in surgery by the American College of Veterinary Surgeons and currently serves as Director of the Veterinary Teaching Hospital’s (VTH’s) Equine Podiatry Unit, as a member of the VTH’s Equine Field Service Section, and as the College’s Equine Extension liaison. Dr. Pleasant’s clinical and research interests include equine podiatry, lameness, and nutrition.

Travis Burns, CJF, TE, AWCF Travis Burns is a Lecturer and the Chief of Farrier Services at the Virginia-Maryland Regional College of Veterinary Medicine (VMRCVM). Burns attended farrier school at the North Carolina School of Horseshoeing. He received his Bachelor of Science degree in Animal Science from North Carolina State University.

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He worked at the North Carolina State University College of Veterinary Medicine before entering into a one-year internship program at Forging Ahead, an elite multi-farrier practice in Northern Virginia. Upon completion of the internship program, he was retained at Forging Ahead as an associate farrier until he joined VMRCVM in 2010. Burns is a Certified Journeyman Farrier (CJF) with a Therapeutic Endorsement (TE) with the American Farriers Association. He is also an Associate in the Worshipful Company of Farriers (by examination) of the United Kingdom.

Rear Hoof Imbalance and its Effect on Hind Limb Lameness

Tracy A. Turner, DVM, MS, DACVS, DACVSMR

The effect of hoof imbalance on fore limb lameness has been well documented. However, rear limb imbalance and its effect on lameness has largely been ignored. The purpose of this presentation is to discuss the common hoof imbalances that occur in the rear hoof, compare those to the fore foot, discuss possible pathophysiology, and finally discuss the effect these rear hoof imbalances have on lameness of the rear leg. The presentation will show how different biomechanics exist between the forelimb and rear limb. Also how rear hoof biomechanics affect the movement (biomechanics) of the upper limb and how these alterations in biomechanics can result in lameness. The rear hoof has only 3 types of hoof imbalance as compared to the front feet which minimally has at least 6. The rear feet develop dorso-plantar imbalance as well as medial to lateral imbalance. Unlike the front feet, contracted heels are very rare problems as are horses with mismatched rear feet. It is not that this cannot occur, but the the incidence is so low, it is of little significance. Finally, in the front feet, small hoof to body size is a significant problem with important prognostic implications, but it has yet to be recognized in the rear feet. Generally speaking, the rear feet are smaller than the front feet and there are no formulas to evaluate this parameter.

Dorsal-Plantar Hoof Imbalance Dorso-plantar imbalance is the most common. The hind hoof is normally slightly more upright than the forefoot, usually by about 5 degrees. But like the front foot, the dorsal hoof wall and the pastern should be in the same alignment. Many factors can affect this. (1) Older horses often show fetlock hyperextension due to suspensory weakness (age related) and this in turn causes a broken forward hoof pastern axis. (2) Pain in the front feet can cause the horse to place its feet further under the body. (3) Long toes and under run heels in the front feet cause a similar postural change. The latter two postural changes cause the heels in the rear feet to be overloaded and subsequently retard the growth of the heels. The heels are the first part of the hoof to distort. Unlike the forelimb where hoof imbalances most frequently lead to foot pain, rear hoof imbalance causes problems higher up in the limb. A broken back hoof axis with a negative solar angle is the most common hoof imbalance of the rear foot. This imbalance causes the hoof to stay on the ground longer than normal. Furthermore, the strain on the deep flexor will be markedly increased over normal before heel lift. This can lead to many lameness issues. The most serious problem is tenosynovitis of the distal tendon sheath. Although this is not the most common lameness caused by this imbalance, because of its effect on the deep flexor tendon, it is the most serious. This can lead to marked swelling in the sheath, pain and even disruption of the blood supply to the tendon. The most common lameness associated with this imbalance is tarsitis, or inflammation of the hock. In a study conducted by the author, the risk factors for horses needing hock injections were evaluated. www.faep.netâ&#x20AC;

The negative solar angle was a common risk factor among all horses needing hock injections. This is probably due to this imbalance causing an increased stance time for the limb. In a different study, this imbalance was associated with a high incidence of gluteal pain in horses. Figure 1: Lateral radiograph of a hind foot showing the most common hind hoof imbalance, negative sole angle. Note how the coffin bone tips up. This causes strain on the deep flexor, delays hoof rollover, and causes hyperextension of the limb.

The hind hooves have a more exaggerated heel first landing than the front hooves. During landing, the rear hooves slide horizontally after the hoof touches the ground. At midstance the coffin joint is maximally flexed and maximal extension occurs at the termination of the stance. Therefore, anything that increases the terminal stance phase will increase joint extension and therefore, dorsal rim pressure on the joints. It is probably the extra work of the flexor muscle and increased strain on the tendon to overcome the negative solar angle of the coffin bone that causes the stress and damage within the tendon sheath. In addition, it is the increased stance phase and increased dorsal rim pressure on the tarsus that create inflammation in the distal tarsal joints. Correction of this imbalance would appear simple. Raise the heels to correct the negative solar angle. However, this causes other problems. The increased heel height further exaggerates the heel first landing. This increases the heel pressure; plus increased heel height increases heel pressure during midstance. In addition, this alters the hoof flight, and riders complain that it changes the gait. A different approach would seem appropriate. Abnormal heel conformation of the hind feet is easy to recognize. When looking at the limb from the side, the digit will show a broken back hoof-pastern axis. The slope of the coronary band from the toe to the heel will have an acute angle. The bulbs of the heels will have a bending appearance and can be seen lying against the shoe palmar to the end of the heel. The dorsal hoof wall begins to take on a "bull nosed" appearance. Looking at the foot from behind, the frog is situated well below the hoof wall and the frog can be seen to prolapse down between the two branches of the shoe. The frog is generally large from the constant stimulation with the ground. Upon removing the shoe, the end of the heel of the hoof wall is located well forward from the base of the frog. The horn tubules will be parallel with the ground. The hoof wall at the heel The Practitionerâ&#x20AC;&#x201A; 19â&#x20AC;&#x201A;

will be thin, there will be no angle to the sole and the bars will be absent. The whole frog will be pushed down below the hoof wall. When the foot is placed on the ground, total weight bearing will be placed on the frog and many horses are reluctant to stand on it when the opposing limb is lifted off the ground. Viewing the ground surface of the foot, there will be a "trough" noted between the apex of the frog and the inner branch of the shoe at the toe. Hoof testers placed on either side of the heel at the angle of the sole will elicit a painful response. Damage to the heels of the hind feet is often easier to improve than damage to the forefeet, possibly due to the difference of the load encountered on the hind limbs vs. the fore limbs. Two methods can be employed to treat this condition. First, allowing a horse to go without hind shoes - if possible - for 4 to 8 weeks can be very effective. This approach can also be used with horses that are resting due to lameness issues. The shoes are removed and the hoof wall at the heels is moved in a plantar direction until solid structures of the hoof wall are encountered. The hoof wall at the toe is lowered appropriately and the edges are rounded. Over the next few weeks, the pressure on the frog will compress and displace the frog until it assumes the same plane as the heels on either side. If the horse needs to continue in work and wear shoes, the approach will be different. The shoes are removed and the heels are moved in a plantar direction until solid horn is established. Excess dorsal hoof wall is removed from toe quarter to toe quarter. The prolapsed frog needs to be compressed in order to have a flat, even plane that includes both the heels and the frog. The back section of a degree pad is cut out to fit over the frog as a mirror image. A thin strip extending across the toe is left attached to the frog wedge and two 4.5 race nails are placed through this strip into the hoof wall at the toe quarters to hold the frog wedge directly over the frog. An Animalintex self-contained poultice is saturated with water and applied so it envelops the whole foot. It is secured to the foot with brown gauze and elastic tape. The horse is now placed in a stall with a firm surface for 24 to 48 hours. During this time, the feet are submerged in a bucket of water a few times to keep the poultice saturated. At the onset of applying the frog wedge, the horse is given 2 grams of phenylbutazone (Bute), as some horses will show mild discomfort and develop a digital pulse. Therefore, when medication is suggested and used, veterinary assistance should be solicited when performing this procedure. When the poultice is removed, the frog will be compressed between the heels, forming a flat, even surface that includes the frog and both heels. The horse can be shod immediately, or can be placed in a stall bedded with sawdust for an additional day to let the feet dry out. The frog will be soft and can be shaped further. Any additional horn at the heels can be removed so the heels of the hoof wall are solid and approach the base of the frog - being careful to keep the frog and both heels in the same plane. A shoe can now be fitted and applied. Shoes on the hind feet are fitted the same as the front where a line is drawn across the widest part of the foot, and the shoe is fitted so the line is placed in the middle of the shoe. In the hind feet, the branches of the shoe may extend marginally beyond the end of the heels. If additional heel elevation is necessary, a wedge pad or a bar wedge can be placed under the heels, as long as the shoe is fitted in the manner just described. This will concentrate the load under the frog and heels rather than behind the heels, which is the case with a long shoe. 20  The Practitioner 

A third approach is to trim the heels as suggested above but trim the front half of the hoof in a different plane. This actually maximizes unrollment of the hoof. The effect has been to reduce strain on tendon sheaths and the deep flexor tendon but it has not been successful in restoring the hoof capsule.

Medio-lateral Imbalance Most people find medio-lateral balance more difficult to assess in the hind feet than in the front feet. The balance of the hoof dictates its placement and affects hoof flight. Because the pelvis, stifle and hock all have some lateral movement, it is easy for a hoof that has worn uneven or has been trimmed out of balance to cause the entire limb to move out of line. Because of the asymmetrical movement of the hock, the hind limb has a slight rotating action as it moves forward over the foot. This is necessary to ensure that the feet are wider than the forelegs when galloping. In many animals this leads to an unnatural wear on the lateral branch of the hoof causing the hoof capsule to be high on the inside. The author’s assessment of rear limb hoof imbalances has corroborated the high medial observation. The rear feet are much

Figure 2: Dorso plantar radiograph of a hind limb showing the second most common hind hoof imbalance. Here we see medial lateral imbalance with the inside wall too long. This is in contrast to the foreleg where the most common medial lateral imbalance is high on the outside wall.

more commonly high medially; in contrast, the front hooves are more likely to be high laterally. This causes change in the horse’s stance. The tendency is for the leg to rotate inward and the limb to be placed more medially. In addition, there are effects on the limb in general. With high medial wall, the limb develops a varus deformity and the fetlock, hock and stifle can each be involved. Many different lameness issues have been attributed to this conformation. Injury to the lateral branch of the suspensory ligament has been noted. In addition, increased pressure on the inside of the joints can cause lameness of the fetlock, hock and stifle. In evaluating rear hoof imbalance cases, the author has noted an increased association with both distal hock lameness and medial femoro-tibial lameness. It is best to assess hind limb hoof balance with both rear legs bearing weight equally. Hind limbs naturally rotate outward and must be assessed from the front and back of the limb. An imaginary line from the hock should bisect the hoof with relatively equal halves. Frequently, the hoof looks out of balance when the foot is raised. With the foot raised, the hock moves towards the Issue 3 • 2014

opposite hind limb and the plantar surface of the distal limb rotates outward along its long axis. Attempting to balance the hoof by sighting down the back of the cannon bone is misleading, and will, in most instances, make the hoof look high on the inside. The best way to assess hoof balance is to use radiography to evaluate how the bones align within the hoof capsule. Accurate identification of key points on the foot, allowing for evaluation of dorsal hoof wall and heel angles, sole depth, and medial and lateral wall height, is not always possible, depending on the technique used and the conformation of the foot. Digital radiography allows improved visualization of soft tissues; however, accurate identification of the coronary band and heels can still be difficult. Edge burn-through (saturation artifact) at the periphery of soft tissues is a common artifact with digital radiography. This in particular, can result in inaccurate assessment of hoof wall thickness. Rigid metallic markers are often used to identify the true border of the dorsal wall; however, accurate identification of the wall length and contour is impossible unless the marker equals the length of the toe and can be contoured to the true shape of the wall. Running a 2-mm bead of barium paste (can be easily stored in and applied from a 60-mL syringe) directly over the dorsal median hoof wall, extending from the coronary band to the tip of the toe, allows for accurate identification of the toe length, wall contour and border, and an appreciation of hoof wall distortion. Due to the increased beam attenuation of the barium paste, a halo artifact (U¨berschwinger) may be seen surrounding the barium, but this will not preclude accurate border identification. Spot marking at (1) the widest point of the proximal (coronary) and distal wall in the quarters, (2) the proximal and distal wall in the heels, and (3) 2.0 to 2.5 cm dorsal to the apex of the frog, will aid in the evaluation of quarter angles, quarter wall height, heel angle and height, sole depth, and toe-to-heel ratio. Marking the dorsal hoof wall becomes very useful in horses with upright feet, with the best example being the club-footed horse. As the foot grows out in these horses, there is a propensity for the dorsal wall to distort and flare, producing multiple angles to the dorsal wall. Radiographic evaluation of the dorsal wall with a conforming marker allows accurate assessment of the distortion of the wall and true angle of the foot. It is crucial that the positioning of the patient, foot, and x-ray beam be flawless when evaluating the foot for the purposes of podiatry. True assessment and measurement of the dorsal hoof wall and heel angle, sole depth, joint congruity, medial to lateral balance, and toe-to heel ratio are dependent on proper positioning. Slight abduction or adduction of the limb or shifting of weight can cause joint incongruity on the horizontal beam dorsal-palmar view. The horse should be placed on a firm, level footing, with the limbs squarely beneath the horse. Limb conformation should also be evaluated prior to taking radiographs. When placing the foot on the positioning blocks, it is important to allow the foot to position itself as dictated by the limb conformation (toed-in, toed-out). To reduce magnification, the foot should be placed on the positioning block in such a way that the foot is as close as possible to the cassette or sensor plate. 

The lateromedial and horizontal dorsopalmar projections are the most useful views to perform when evaluating the foot for conformation and balance. Consideration of the area of interest, as well as having solid anatomical knowledge of the horse's foot, is important when performing these radiographic views. The lateromedial (L-M) projection is performed with the horse standing squarely on a flat, level surface with each foot on a positioning block of equal height. It is important that the cannon bone be perpendicular to the floor in both the medialto-lateral and dorsal-to-palmar planes. Keeping the horse's head and neck straight is also important to reduce the influence of uneven loading of any one limb. Focal-film distance usually ranges between 24 and 28 inches; it is important to be consistent, and once the technique is established, that the focal-film distance remains constant. Once the horse is positioned squarely, proper beam alignment and positioning is the next step in obtaining a workable image. If the area of interest is the distal phalanx and the purpose of the study is evaluating foot balance and symmetry, the center of the beam should be aimed 1.5 to 2.0 cm proximal to the weight-bearing surface and midway between the toe and the heel; the beam angle should be parallel with the heel bulbs and the ground surface. This beam alignment will produce a film that shows the medial and lateral solar margins and palmar processes of the distal phalanx superimposed on one another (in the "normal" foot). Any obliquity in the image can be corrected by raising or lowering the central beam to adjust for variation in sole depth, or adjusting the beam angle in relation to the heel bulbs. Correct positioning reduces the likelihood of artifactual changes to the joint space that might otherwise be interpreted as joint asymmetry and foot imbalance. This projection allows evaluation of medial to lateral balance and conformation of the foot with observation and measurement of the medial and lateral wall length and angle, and the orientation of the distal phalanx within the hoof capsule. Orientation of the distal phalanx can be assessed by measuring the distance from the articular surface of the distal phalanx to the ground surface; the solar canal can also be used as a reference point, but it is less consistent. Using the solar margin as a point of reference can be variable due to changes that can occur in the bone. In horses with "ideal" conformation, the articular surface of the distal phalanx is parallel to the ground, as is a line between the medial and lateral coronary band. In addition, the medial and lateral walls are of equal thickness, and the distances from the medial and lateral solar margins to the ground are similar. In horses with significant rotation or

Figure 3: Lateral radiograph illustrating one method of correcting a negative sole angle. In this case, the hoof was shod in 2 planes, the caudal plane puts the heels and frog in a flat plane and the dorsal half of the hoof is radically rockered.

The Practitioner  21 

angulation in the distal limb, the relation of the distal phalanx with the ground may not be as symmetrical. Furthermore, the distal interphalangeal joint space should be approximately even across its width regardless of angulation of the phalanges. It is normal for the medial quarter wall to be at a slightly steeper angle and subsequently measure shorter in length. However, caution in overinterpretation of joint incongruency is recommended, because any malpositioning of the limb or foot can create the appearance of medial to lateral imbalance. Using radiographs to assess the relationship between the hoof and the underlying osseous structures as an aid in assessing foot balance is about developing an understanding of the relationships between the position of the hoof capsule, the angle of the distal phalanx within the hoof capsule, the symmetry of the interphalangeal articulations, and the alignment of the phalanges.

References: 1. Colles C, Ware R: The Principle of Farriery, London, J.A.Allen, 2010, pp 157-162. 2. Back W, Clayton H: Equine Locomotion, Edinburgh, Elsevier, 2013, pp 127-147. 3. Eggleston RB: Value of Quality Foot Radiographs and Their Impact on Practical Farriery, Proc of Am Assoc Eq Practnr, 2012, pp 164-175. 4. O’Grady SE, Merriam JG: Low Heels in the Hind Feet-An Often Overlooked Problem, Am Farriers J, March/April 2007.

Tracy A. Turner, DVM, MS, DACVSMR Dr. Tracy Turner apprenticed with a farrier in 1972, and used those skills to help finance his education. He received his DVM degree from Colorado State University in 1978, after which he was able to pursue his interest in equine medicine and surgery. He interned at the University of Georgia and completed a surgical residency and Master's degree at Purdue University. He has served on the faculty of the University of Illinois, University of Florida and the University of Minnesota. He joined Anoka Equine Clinic in 2004, where his responsibilities include Sports Medicine, Lameness, and Surgery. Dr. Turner's primary area of research interests has focused on equine lameness with particular interest in equine podiatry and thermography. He has spoken nationally and internationally on lameness topics. He has written over 100 peer-reviewed manuscripts, over 250 non-peer-reviewed papers, and more than 30 book chapters on equine lameness, podiatry and thermography. He is board certified by the American College of Veterinary Surgeons and the American College of Veterinary Sports Medicine and Rehabilitation. He is a Fellow of the American Association of Thermology.

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22  The Practitioner 

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Issue 3 • 2014

Treatment Options for Sepsis of the Digital Flexor Tendon Sheath Ted A. Broome, DVM, DACVS Infection of the digital flexor tendon sheath (DFTS) can be potentially life-threatening or a career-ending condition for affected horses. Survival rates for horses presented for DFTS sepsis range from 71–90%, whereas 43–100% of surviving horses are reportedly able to return to their previous levels of performance after treatment. The overwhelming majority of cases of tendon sheath infection occur as a result of lacerations or puncture wounds occurring in the palmar/plantar aspect of the distal limbs. Septic tenosynovitis of the DFTS has been documented, although far less frequently, following intrathecal injection, DFTS tenoscopy, annular ligament transection, and regional perineural analgesia. Lacerations or puncture wounds of the tendon sheath introduce bacteria directly into the sheath. Initially, these wounds may only be contaminated with bacteria without establishment of infection. If tendon sheath involvement is diagnosed and treated aggressively within the first 6-8 hours after injury, establishment of infection may be avoided. However, since horses with wounds of the tendon sheath may not display signs of infection for several days after injury, veterinarians are often presented with these cases well beyond this time frame.

CLINICAL FINDINGS AND DIAGNOSIS Early diagnosis and treatment of tendon sheath infection is important to provide the best potential for successful treatment and to return the horse to its previous level of athletic performance. Horses with an infected DFTS are often extremely lame (4-5/5), although the lameness may be less pronounced if the tendon sheath is open and draining effectively. Tendon sheath effusion may be present along with soft tissue edema, swelling, and heat, and there may be pain on direct digital pressure to the sheath and flexion of the distal limb. In the case of lacerations, synovial fluid may be Fig. 1 - Partially sutured laceration observed exiting the wound, of plantar fetlock. Synovial fluid can be seen draining from the wound or can possibly be expressed indicating tendon sheath involvement. by applying pressure to the sheath (Figure 1). An attempt to obtain synovial fluid for cytological analysis and culture should be made in all cases of suspected tendon sheath infection or contamination, as synovial fluid evaluation 

can confirm the diagnosis of synovial sepsis and may assist in antibiotic selection. However, synovial fluid collection may not be possible if the sheath is open and draining. In those cases where a wound is present, a site distant to the wound in nontraumatized tissue should be aseptically prepared for centesis. Sites for synoviocentesis of the DFTS include the proximolateral pouch, distal palmar/plantar pouch, basilar sesamoidean approach, and axial sesamoidean approach. Normal synovial fluid usually contains fewer than 500 cells/ul, with the majority of cells being mononuclear cells. Synovial fluid white blood cell counts of greater than 30,000 cell/ul that are primarily neutrophils, and total protein concentrations of 3.5 to 4.0 g/,dl are consistent with infection. A portion of synovial fluid should also be submitted for culture and sensitivity, as identification of the causative organisms and antimicrobial susceptibility patterns can guide appropriate antibiotic therapy. However, since bacteria may not be successfully cultured and identified from synovial fluid samples even in the presence of ongoing infection, failure to culture an organism does not rule out infection. Incubating synovial fluid in blood culture medium for 24 hours has been shown to increase the probability of successful bacterial culture. In order to document synovial involvement when a wound is present, a site distant to the wound is aseptically prepared, a needle inserted and sterile isotonic fluid is infused into the tendon sheath under pressure. Observation of fluid exiting the wound confirms involvement of the tendon sheath. Radiographic evaluation of the region is useful to document the presence of radiopaque foreign material Fig. 2 - Lysis of medial sesamoid bone present in the tissues, the consistent with septic osteitis from presence of concurrent extension of DFTS infection. bone damage, or evidence of extension of an ongoing septic process into adjacent bone (Figure 2). Additionally, in order to confirm wound involvement with the tendon sheath, contrast material can be injected into the sheath and subsequent radiographs evaluated for the presence of contrast material exiting the wound.


Systemic Antimicrobials

Systemic antibiotics are indicated in all cases of DFTS infection. Treatment with antibiotics should not be delayed while waiting on culture results. The initial antibiotic regimen should consist of The Practitioner  23 

broad spectrum intravenous antibiotics and can be made based on those bacteria most likely to be identified in orthopedic infections. The most common bacterial isolates identified in a retrospective study of 192 horses with septic arthritis or tenosynovitis were enterobacteriaceae, streptococci, staphylococci, and other gram negative bacteria. Potassium penicillin and gentamicin are used most commonly to treat synovial infections, but combinations of penicillin and either amikacin, ceftiofur, or enrofloxacin are also used. Antibiotic therapy can be adjusted based on results of culture and sensitivity. Intravenous antibiotics should be continued for at least 7-10 days. After that time, and based on response to therapy, the horse can be switched to oral antibiotics for 2-4 weeks.

Local Antibiotic Therapy

Elimination of bacterial infection from the tendon sheath is a critical component of therapy. Penetration of systemic antibiotics to the synovium of infected synovial structures is often poor due to synovial vascular injury, ischemia, necrosis, and pannus formation. However, high sustained local concentrations of antibiotics can be achieved in synovial structures by intrasynovial injection, regional limb perfusion, or placement of antibiotic impregnated polymethylmethacrylate (PMMA). Intrasynovial antimicrobials. Initial studies evaluating intraarticular administration of 150 mg of gentamicin demonstrated that concentrations in synovial fluid remained well above the MIC for many bacterial pathogens for 24 hours. Currently, amikacin (250-500 mg) is preferred for intrasynovial injection due to its increased spectrum of activity over gentamicin. Other antibiotics that can be used include gentamicin (200-500 mg), cefazolin (500 mg), penicillin (2-5 x 106 IU) and ceftiofur (500 mg). Antibiotics should be injected every 24-48 hours. Regional limb perfusion. Regional limb perfusion (RLP) with antibiotics has been shown to be a safe and effective method to treat infection of synovial structures in the distal limb. High concentrations of the antibiotic can be achieved in the synovium and surrounding soft tissue structures. In a recent study, fetlock synovial fluid amikacin concentrations between 61 and 91 times the MIC for common susceptible bacterial pathogens that cause orthopedic infection in horses were achieved after RLP with 2 grams of amikacin. Regional limb perfusion is most commonly performed by injection of antibiotic into a superficial vein (Figure 3), but can also be performed by the intraosseous route. For treatment of DFTS infection, a tourniquet Fig. 3 - Intravenous regional perfusion is placed proximal to of antibiotics administered via the the carpus or hock, and saphenous vein. the antibiotic of choice is diluted in 30 to 60 mL of sterile saline and injected into the cephalic or saphenous vein. The tourniquet is left in place for 30 minutes to allow diffusion of antibiotic across the pressure 24  The Practitioner 

gradient into the tissue. Amikacin is the most commonly used antibiotic for RLP, but other water-soluble concentrationdependent antibiotics may be used. The dose used for RLP is empirical, but generally, a dose of 1/3 to ½ of the recommended systemic dose is used. The dose of amikacin used most often is 0.5 to 1 gram. Antibiotic impregnated PMMA. PMMA is a high density polymer formed by combining a fluid monomer and powdered polymer. When antibiotic is added to the PMMA at the time of mixing, it becomes suspended in the hardened compound. The PMMA can be formed into small beads and strung onto suture or stainless steel wire to be placed in the tendon sheath. Once the PMMA is placed into a wound, the antibiotic diffuses into fluid in the local environment across a concentration gradient. Antibiotic is released in a bimodal fashion, with the majority released into the surroundings within the first few days, followed by a slow, gradually decreasing release over time. Local concentrations of antibiotics can reach up to 200 times the concentrations achieved by systemic administration. Antimicrobials used in PMMA should be bactericidal and heat stable. Those most commonly used in horses include gentamicin, tobramycin, amikacin, and cefazolin, and are mixed in a quantity of 1-2 grams antibiotic per 10-20 grams PMMA.

TENDON SHEATH LAVAGE/DRAINAGE The goals of tendon sheath lavage are to reduce the bacterial population, remove inflammatory mediators, accumulated fibrin, and foreign material, and to decrease synovial distension and pain. This can be accomplished by through and through lavage, tenoscopic-guided lavage, passive drainage through existing wounds, or tenosynoviotomy. Tenoscopic lavage/drainage. Lavage under tenoscopic guidance is the preferred method for lavage of an infected tendon sheath, especially in those cases involving wounds of over 24 hours duration. Benefits of tenoscopy include increased access throughout the sheath and a more thorough lavage, removal of foreign material and fibrin, ability to perform Fig. 4 - Tenoscopic view demonstrating a synovectomy if needed, damage to the deep digital flexor and the ability to assess tendon. the extent of tendon damage (Figure 4). A thorough tenoscopic examination of the tendon sheath may be limited in the case of open wounds that prevent adequate distension of the sheath. Through and through lavage/drainage. Through and through lavage has the advantage of being relatively simple to perform and less expensive than tenoscopic-guided lavage. This technique may be appropriate for DFTS lavage early (less than 24 hours) after an injury involving the sheath or in less severe infections with minimal fibrin formation. Lavage can be performed using 14 gauge needles but a more effective lavage can be achieved using ingress and egress arthroscopic cannulas. Disadvantages of Issue 3 • 2014

through and through lavage include the inability to thoroughly lavage all areas of the sheath, remove foreign material, accumulated fibrin, or synovium, and to evaluate the tendons. Passive drainage. In those horses with chronic wounds involving the sheath, continued drainage through the wound after lavage may be beneficial in some cases. Continued drainage can be achieved by leaving the original wound or a partially closed wound open to heal by second intention, or by enlarging existing small wounds. Continued drainage results in removal of inflammatory mediators and synovial fluid and may lead to increased comfort. The continued presence of an open wound into the sheath provides a route for re-infection or superinfection of the sheath, and as such, strict asepsis must be maintained during bandage changes. Tenosynoviotomy. A technique for treating cases of DFTS sepsis refractory to initial treatment via open palmar/plantar annular ligament transection and tenosynoviotomy with passive drainage has recently been described. The surgical technique involves a longitudinal incision through skin, the palmar/plantar annular ligament and the DFTS, along with tenotomy of the distal lateral branch of the superficial digital flexor tendon. This approach allows for thorough examination and debridement of the tendon sheath, after which, the wound is allowed to heal by second intention. The authors reported that 5 of 7 horses available for follow up were considered by their owners to be serviceable for their intended use, while 2 horses were euthanized because of intractable DFTS sepsis. They concluded that tenosynoviotomy is a viable salvage procedure in cases of chronic, refractory DFTS infection. Deep digital flexor tenectomy. Tenectomy of the intrathecal component of the deep digital flexor (DDF) tendon has been described as a treatment for refractory DFTS sepsis when there is concurrent septic DDF tendonitis. In a recent report of 4 horses undergoing DDF tenectomy, all 4 horses survived and were comfortable at pasture. One of the 4 horses was sound at a trot, while the remaining 3 were mildly lame at a trot. Only the necrotic portion of the DDFT, ranging from 5 to 15 cm, was removed. The authors concluded that DDF tenectomy should be considered as an alternative to euthanasia in cases of DFTS sepsis complicated by septic DDF tendinitis. Nonsteroidal antiinflammatory drugs (NSAIDs). The use of NSAIDs is a key component of any treatment strategy for DFTS sepsis. NSAIDs decrease the production of inflammatory mediators, especially prostaglandin E2, that are responsible for local tissue damage, swelling, and pain. Analgesia provided by NSAIDs increases use of the affected limb and movement of the tendons within the tendon sheath which aids in decreasing intrathecal adhesion formation. Increased comfort provided by NSAIDs decreases loading of the contralateral limb and aids in preventing contralateral limb laminitis. Phenylbutazone is used most commonly and is administered at a dose of 2.2-4.4 mg/kg orally or intravenously every 12 hours. Flunixin meglumine, 1.1 mg/kg orally or intravenously every 12 hours, and firocoxib, 0.1 mg/kg orally every 24 hours, are alternative choices.

PROGNOSIS As indicated previously, the outcome for horses with DFTS infection can be highly variable, both for life and for return to intended use. Inability to resolve the initial tendon sheath 

infection, extension of infection into adjacent structures and development of contralateral limb laminitis are the most likely reasons for euthanasia in affected horses, whereas intrathecal adhesion formation or local soft tissue damage can limit full return to soundness. Early recognition of DFTS involvement in distal limb wounds and aggressive initial therapy will increase the likelihood of a successful outcome.


1. Baxter GM: Management of wounds involving synovial structures in horses. Clin Tech Equine Pract 3:204-214, 2004 2. Frees KE, Lillich JD, Gaughan EM, et al: Tenoscopic-assisted treatment of open digital flexor tendon sheath injuries in horses: 20 cases (1992-2001). J Am Vet Med Assoc 220:18231827, 2002 3. Joyce J: Injury to synovial structures. Vet Clin North Am Equine Pract 23:103-116, 2007 4. Kelmer G, Bell GC, Martin-Jimenez T, et al: Evaluation of regional limb perfusion with amikacin using saphenous, cephalic, and palmar digital veins in standing horses. J Vet Pharmacol Therap 36:236-240, 2012 5. Lopes MAF, Sullens KE, Walker BL: Tenoscopy in 33 horses with septic and nonseptic digital tenosynovitis (1997-2001). J Equine Vet Sci 26:27-31, 2006 6. Marsh CA, Watkins JP, Schneider RK: Intrathecal deep digital flexor tenectomy for treatment of septic tendonitis/ tenosynovitis in four horses. Vet Surg 40:284-290, 2011 7. McNally TP, Slone DE, Hughes FE, et al: Tenosynoviotomy for sepsis of the digital flexor tendon sheath in 9 horses. Vet Surg 42:114-118, 2013 8. Rubio-Martinez LM, Cruz AM: Antimicrobial regional limb perfusion in horses. J Am Vet Med Assoc 228:706-712, 2006 9. Smith LJ, Mellor DJ, Marr CM, et al: What is the likelihood that a horse treated for septic digital tenosynovitis will return to its previous level of athletic function? Equine Vet J 38:337341, 2006 10. Wereszka MM, White NA, Furr MO: Factors associated with outcome following treatment of horses with septic tenosynovitis: 51 cases (1986-2003). J Am Vet Med Assoc 230:1195-1200, 2007

Ted A. Broome, DVM, DACVS Dr. Ted Broome received his DVM degree from North Carolina State University in 1986. He completed an internship in large animal medicine and surgery at the University of Georgia and completed a large animal surgical residency at the University of Florida in 1993. He has practiced in both the academic and private practice setting since that time. He is board certified by the American College of Veterinary Surgeons and is currently a Post Doctoral Associate in University of Florida College of Veterinary Medicine’s Equine Performance Laboratory. He presently serves as Commander of the 358th Medical Detachment (Veterinary Services) in Montgomery, AL. Dr. Broome’s research focuses primarily on the effect of NSAIDs on equine muscle growth and repair.

The Practitioner  25 

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NO GENERIC ® ADEQUAN Get the facts at BRIEF SUMMARY : Adequan® i.m.: For the intramuscular treatment of non-infectious degenerative and/or traumatic joint dysfunction and associated lameness of the carpal and hock joints in horses. There are no known contraindications to the use of intramuscular Adequan® i.m. brand Polysulfated Glycosaminoglycan in horses. Studies have not been conducted to establish safety in breeding horses. Each 5 mL contains 500 mg Polysulfated Glycosaminoglycan. WARNING: Do not use in horses intended for human consumption. Not for use in humans. Keep this and all medications out of the reach of children. Caution: Federal law restricts this drug to use by or on the order of a licensed veterinarian. Adequan® I.A.: For the intra-articular treatment of non-infectious degenerative and/or traumatic joint dysfunction and associated lameness of the carpal joint in horses. Inflammatory joint reactions and septic arthritis have been reported following administration of Adequan® I.A. Joint sepsis, a rare but potentially life threatening complication, can occur after intra-articular injection. Use only in the carpal joint of horses. Each 1 mL contains 250 mg Polysulfated Glycosaminoglycan. WARNING: Do not use in horses intended for human consumption. Keep this and all medications out of the reach of children. Caution: Federal law restricts this drug to use by or on the order of a licensed veterinarian. SEE PRODUCT PACKAGE INSERTS FOR FULL PRESCRIBING INFORMATION. Adequan® is a registered trademark of Luitpold Pharmaceuticals, Inc. ©LUITPOLD PHARMACEUTICALS, INC., Animal Health Division, Shirley, NY 11967. AHD 010, Rev. 2/2014

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Based on Market Dynamics, Inc. AHS study data for period from Q12004 through Q42013. Ranking represents cumulative dollar sales volume over the period. Madigan J and Pusterla N. Life Cycle of Potomac Horse Fever – Implications for Diagnosis, Treatment, and Control: A Review. AAEP Proceedings. 2005;51:158-162. Hamende V. Potomac horse fever cases confirmed in northern Wyoming. University of Wyoming Cooperative Extension Service. Press Release, September 13, 2002. Available at Accessed May 15, 2014. 4 Williams, N. Potomac Horse Fever. Eq Dis Quart. 2012;21(1):4-5. 5 Potomac Horse Fever. Available at Accessed May 15, 2014. 1

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2014 Practitioner Issue 3  
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