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What is a Popped Splint?
by Lori M. Smolkovich, DVM
One day as you are getting ready to ride your horse, you notice a bump around the cannon bone. Your horse seems sensitive to palpation, but overall is sound. You ask for advice from other people in the barn. They say it is a "popped splint", and before you know it, you are being flooded with advice and opinions leaving you confused and unsure of what to do. This is a common scenario we as veterinarians hear all the time. There seems to be some confusion among horses owners regarding metacarpal exostosis, better known as "a popped splint" or "splint". In this article, the different types of "splints" will be discussed, along with cause, diagnosis, treatment, and prevention.
Before discussing "splints" and how they occur, some anatomy needs to be reviewed. In the front leg, the horse has metacarpals II, III, and IV. The third metacarpal bone is the cannon bone. The second and fourth metacarpal bones are called splint bones because they are on either side of the cannon bone, "splinting" the leg. The second metacarpal bone is on the medial (or inside) of the cannon bone and the fourth metacarpal bone is on the lateral (or outside) of the cannon bone. The splint bones are held tightly against the cannon bone by the interosseous ligament (inter=between, and osseo=bone). In the hind leg, the anatomy is the same except instead of naming the bones metacarpals, the term is metatarsals.
What is a "splint"?
There are four types of "splints" but only two are common and noticed by horse owners. Those will be the only two types discussed in this article.
True splint: A true splint is tearing of the interosseous ligament. These tears most frequently occur on the medial (or inside) of the leg between the medial splint bone and the cannon bone. Usually the tear is in the proximal third (top third) of the leg. The body's way of repairing itself, is to deposit calcium into the tear to make the area stronger. The "bump" that the owner feels on the leg is a result of inflammation and the deposited calcium.
Traumatic splint: A traumatic splint is the result of trauma to the periosteum. Periosteum is a dense fibrous membrane that covers the surface of bones. As a result of trauma, the periosteum becomes inflamed. If there is sufficient inflammation, the bone will heal itself by depositing calcium. The degree of inflammation is dependent on the level of trauma and the way in which the horse's body responds to that trauma. This is why some bumps are temporary and resolve when the inflammation subsides, and some are permanent, due to calcification deposition. A traumatic splint can occur on the cannon bone or either splint bone.
Why do "splints" occur?
True splints, as already stated, are a result of the interosseous ligament tearing, and that these tears most frequently occur between the cannon bone and medial (or inside) splint bone. A better understanding of anatomy and biomechanics are needed to explain why this happens. When a horse bears weight on a front leg, the lower row of carpal (knee) bones and the medial (inside) splint bone articulate (join) in a way that causes the medial (inside) splint bone to be pushed down and back. If a horse is overworked, or if the area is overloaded, the interosseous ligament cannot handle the stress of being pushed in two different directions, and it tears. Offset carpi, also known as benched knees, is a conformational abnormality that can also cause true splints even if a horse is not overworked. As horses age, the interosseous ligament naturally disappears as the splint bones fuse to the cannon bone. This is why true splints are usually a condition of younger horses, because in older horses, the ossified interosseous ligament can handle a much more demanding workload.
A traumatic splint can occur in many ways; getting kicked by another horse, interference (hitting one leg with the foot from the opposite limb), or hitting objects, are common occurrences. If the "splint" is on the outside of the leg, it is probably the result of external trauma, such as hitting a rail while jumping or being kicked by a pasture mate. If the trauma is on the inside of the leg, interference is the most common cause. Several conformational abnormalities predispose a horse to interfering which can result in "splints". Base narrow horses or toe out conformations are naturally occurring conformational abnormalities, but improperly trimmed and/or shod horses can cause abnormal foot flight and as a result, interference occurs.
Diagnosing a "splint"
A "splint" diagnosis is usually fairly straightforward. There is heat, pain, and swelling over the bump. It is very sensitive to palpation and horses are usually mildly lame at the trot on hard footing. A radiograph should be taken to confirm it is a "splint" and not a fractured splint bone, which is a more serious condition. Although the "splint" by itself is usually a temporary lesion with no real long term consequences, it can affect other structures and cause big problems. The suspensory ligament runs in between the two splint bones. Inflammation or calcification deposition that is caused by "splints" can impinge on, or interfere with the suspensory ligament which can have serious effects on the horses long term use. This is why ultrasonic examination is often recommended. Through ultrasound, the suspensory ligament can be assessed. This gives your veterinarian a complete picture of what is going on and the best way to treat your horse.
The goal of treating a "splint" is to reduce inflammation. This is done by the use of non-steroidal medications, like bute, ice therapy, and wrapping the affected limb. Some veterinarians recommend DMSO or a DMSO/furazone sweat wrap underneath the bandage to further treat inflammation. Rest is given until the inflammation has subsided and the horse is sound. This usually takes approximately a month. If suspensory ligament involvement is suspected, treatment is usually more aggressive using intralesional corticosteroid injections, or shockwave therapy in addition to the inflammation reducing techniques already listed.
The likelihood of splints occurring in your horse can be minimized but not completely eliminated. You can not change the way your horse moves or conformation. But by making sure your horse is properly trimmed, not overworking, and having protective wraps or boots on your horse while being turned out and ridden, can help minimize any trauma that might occur.
Should you consider buying a horse with a "splint"?
Overall, "splints" usually cause a temporary lameness with no long lasting problems. Once the inflammation has resolved, the bump that is left is nothing more than a cosmetic blemish. Before considering purchasing a horse with a splint, the splint should be thoroughly evaluated by your veterinarian to ensure the suspensory ligament is not effected and that the splint is not still inflamed or causing problems. The cause of the splint should also be investigated. If the horse has poor conformation, or a tendency for interference when ridden, then there is the likely chance that "splints" will be an ongoing problem.
Stashak, Ted. "The Metacarpus and Metatarsus." Adams' Lameness in Horses. Fifth ed. Philadelphia: Lippincott Williams and Wilkins, 2002. 818-821. Print.
Rooney, James R. "The Abnormal Foreleg Shoulder to Fetlock." The Lame Horse. First ed. Neeah: Russell Meerdink, 1998. 57-60. Print.
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Common Equine Parasites and Deworming Strategies
Deworming protocols are a common discussion amongst barn managers, horse owners, and veterinarians. In order to understand various deworming strategies and apply the one that works best for your horse, you have to know the common parasites that affect the horse.
In years past, Strongylus vulgaris (large strongyles) was the equine parasite of most concern. Large strongyles take approximately two months from the time they are ingested by the horse until they are shed in the manure to further contaminate the pasture. Thus the traditional rotational deworming strategy was developed and adequately controlled large strongyle infections. However, large strongyles are rarely an issue in managed horse populations today, and therefore rotational deworming is no longer needed or recommended.
Cyathostomins, or small strongyles, are considered the major adult equine parasite. Small strongyles are pervasive and infect grazing horses everywhere. Luckily, small strongyles typically only produce disease when the parasitic burden is severely elevated, although they can result in disease at lower levels if the horse’s immune system is compromised in some other way. Since low levels of small strongyles do not result in disease and large strongyles are well controlled in today’s horse populations, frequent deworming is no longer necessary, rather properly timed deworming during the seasons of heavy parasitic burden and transmission is ideal.
Anthelmintic (dewormers) resistance is becoming a problem that can be delayed and hopefully controlled with the use of fecal egg counts (FEC), proper pasture management, and appropriately timed deworming for that particular environment. Parasite refugia is a common term used by parasitologists and veterinarians that refers to the population of parasites that survive the administered anthelmintic; this includes the stages of parasites that are not affected by that drug, the parasites within the horses that were not treated, and all of the living parasite stages on pasture. The larger the proportion of parasites in refugia, the slower resistance can develop. Therefore, it is advised to perform fecal egg counts on your horses biannually and deworm according to parasitic burden so that only a proportion of the horses in the herd will be dewormed at that time rather than deworming all of the horses at once. Another management tactic to slow anthelmintic resistance is to avoid rotating pastures right after deworming as this eliminates the dilution effect. Lastly, avoiding deworming during periods of low parasite transmission/low pasture refugia is advised. Low pasture refugia occurs during periods of extreme temperatures because larvae (parasite eggs) cannot survive in harsh weather, such as the winters in the north or the summers in subtropical and tropical environments.
It is also important to understand that some horses are more sensitive to small strongyle infections, and therefore will always shed more eggs than others. In fact, 20-30% of adult horses in a herd shed approximately 80% of the total eggs. Therefore, horses are divided into three categories based upon their FEC numbers: low (0-200epg), moderate (200-500epg), and heavy shedders (>500epg). On average, if a horse’s FEC is over 200 eggs per gram (epg) then he/she should be dewormed, although individual veterinarians may have different cutoff values. Moderate and heavy egg shedders may require more frequent deworming than twice a year.
Other gastrointestinal parasites that affect the adult horse are Anoplocephala perfoliata (tapeworms), Oxyuris equi (pinworms), and Gasterophilus spp. (bots).
· >Tapeworms are spread through the ingestion of an oribatid mite commonly found on grass pastures. These mites live in moist areas, and therefore tapeworms are usually not an issue in arid environments. Tapeworms have the potential to result in various types of colic. They cause small mucosal erosions at the site of attachment, which can be painful. Also, an infection with tapeworms can result in an ileocecal impaction or a spasmodic colic if the burden is high enough. Tapeworm eggs are intermittently shed in the manure and can be easily missed on fecal floats. Therefore, it is important to deworm with an anthelmintic once a year that is efficacious against tapeworms, such as praziquantel (sold in combination with ivermectin or moxidectin) or a cestocidal dose of pyrantel pamoate. It is recommended to treat for tapeworms in the late fall or early winter.>
· >Pinworms have historically been an issue with young horses; however, they have become increasingly more common in adult horses recently. Pinworm eggs are deposited on the perineum and perianal regions and result in pruritus (an itching sensation), which can lead to intense tail rubbing and skin excoriations. The tail rubbing in addition to sharing grooming materials and tail wraps can spread the pinworms to other horses. The best way to control pinworms is to deworm when clinical disease is present. Ivermectin, moxidectin, pyrantel pamoate, or fenbendazole will eliminate a pinworm infection. Additionally, it is recommended to wash the perineum and perianal regions to provide relief of pruritus and to decrease transmission to other horses.>
· >Bots rarely result in disease but are aesthetically displeasing. Therefore, deworming annually in late fall or early winter will help to decrease transmission the following season. Ivermectin or moxidectin are the only anthelmintics available at this time that are efficacious against bots.>
Parascaris equorum (roundworms) is the primary parasite of foals and weanlings. Infections can result in poor growth, airway inflammation (cough, nasal discharge), and small intestine impactions. Small intestine impactions and subsequent fatal intestinal ruptures can occur when foals/weanlings with a heavy roundworm infestation are dewormed with an efficacious anthelmintic. Small intestine impactions are not seen when foals/weanlings are dewormed with fenbendazole, and therefore that is the drug of choice when deworming foals for the first time. During the first year of life, foals/weanlings should be dewormed a minimum of 4 times beginning at 2-3 months of age with fenbendazole. The second deworming should occur just prior to weaning, and the drug of choice will depend on whether primarily small strongyles or roundworms are seen on the fecal float. The third and fourth dewormings should be performed at 9 and 12 months respectively and they should target small strongyles (ivermectin or moxidectin).
In summary, small strongyles are the parasite of most concern for adult horses today. Having a fecal egg count done on your horse at least twice a year to determine his/her parasitic burden is essential. Deworming at least twice a year is recommended, with additional dewormings as needed based on the parasitic burden of the individual horse. Deworming in late fall or early winter with praziquantel (found in combination with ivermectin or moxidectin) is essential to treat for any tapeworm burden or bot infestation. Discussing your horse(s) with your veterinarian to develop an appropriate deworming strategy is the most important way to keep your horse(s) healthy.
Kristina McGinnis, DVM
New England Equine Medical and Surgical Center
AAEP Parasite Control Guidelines
Reading between the Lines: White Line Disease
What is it?
White line disease (WLD), is a multifactorial process that leads to a progressive separation of the inner zone of the hoof wall. The white line of the hoof can be visualized on the sole, and is the junction of the insensitive laminae of the hoof wall and the horn of the sole. The hoof wall consists of three layers: the stratum externum (external layer), stratum medium (middle layer), and stratum internum (inner layer). In WLD, the hoof wall separates from the underlying laminae (stratum internum) at the level of the stratum medium, also known as the tubular horn. When we use the term "white line disease", we are referring to the fact that the horse has some degree of separation of the hoof wall from its laminar attachments. Typically, the condition begins with a crack or opening within the white line, which then allows bacteria or fungus to enter the stratum medium. Since this is closely associated with the laminae, cavities subsequently develop between the laminae and outer hoof wall.
What causes it?
White line disease can affect a horse of any sex, age or breed, barefoot or shod. Mechanical stress, inappropriate farriery, genetic factors, and environmental conditions may all play a role in the development of WLD. Poor hoof hygiene has often been held responsible for the development of WLD, however it remains questionable as the initiating cause. It is believed that the primary event is mechanical stress on the inner hoof wall such as from poor hoof conformation or less than ideal farriery. These include, excessive toe length, poor hoof conformation, and various hoof capsule distortions such as long toe-under run heel, clubfoot, or sheared heels. This stress leads to breakdown of the hoof's natural barrier, and allows invasion of opportunistic bacteria that possess keratinolytic enzymes. These bacteria digest the hoof horn, leading to the progression of the separation proximally towards the coronet band. If left untreated WLD will become extensive and displacement of the distal phalanx can become a sequel.
How do we diagnose it?
Clinical signs for WLD can vary and the degree of lameness present can range from non-existent to severe. Some horses may show a positive reaction to hoof testers while others may not. This is why it is very important to start the diagnostic process with a thorough physical exam and lameness evaluation. As WLD becomes moderate to severe, damage is sufficient to allow mechanical loss of the attachment between the laminae and the inner hoof wall, clinical signs of pain (typically lameness) can be seen. When examining the foot from the solar surface, there is often a visual confirmation of a separation between the hoof wall and underlying laminae. Looking even deeper into the inner hoof wall, the inner white line will typically show a separation filled with a grey/white powdered horn material. A probe can be used to further explore the depth and extent of the cavitation. Additionally, a hollow sound is typically heard if the outer hoof wall is percussed with a hammer. WLD should be differentiated from other common foot lameness that will block out to a palmar digital block, such as chronic laminitis and foot abscesses. If lameness is present on initial evaluation, a thorough lameness examination should be performed including nerve blocks to confirm the suspected area followed by radiographs. When extensive hoof wall damage is present and subsequently pain, WLD can mimic laminitis both clinically and radiographically, and thus it is important to differentiate between the two.
Radiographs should be taken to show the extent of separation between the hoof wall as well as to rule out laminitis. A lateral and dorsopalmar view are generally sufficient to allow for accurate interpretation of WLD. In chronic cases of WLD, pedal osteitis has been seen as a sequelae. Radiographs also allow for better visualization of the hoof capsule and can help with trimming and shoeing the horse in the future.
How do we treat it?
When treating WLD, corrective trimming is imperative to remove abnormal stresses on the hoof wall, in conjunction with resection and debridement of the entire extent of the separated hoof wall until the firm, healthy adhesion of the hoof wall to the underlying stratum internum can be seen. Resection of the hoof wall is performed using hoof nippers, a hoof knife, and motorized tools.
Adjunctive shoeing techniques are then applied to provide adequate support to the remaining foot and to remove stress from the affected part of the foot. A heart bar or egg bar shoe redistributes weight-bearing forces to the frog and palmar region of the foot and away from those damaged and therefore weakened areas. Resilient putty is typically used in conjunction with shoe to provide distal phalanx support, especially if displacement of P3 (coffin bone) is a concern. Additionally, it is important that the hoof remains clean and dry. The horse must be kept in a dry stall after treatment, and drying agents (ie. iodine) can be applied to the resected area to prevent excessive moisture from building up. The affected hoof should be cleaned daily with a wire brush. Systemic medical therapy is not required in conjunction with the resection since this disease is limited to the keratinized area of the hoof wall. Plastic acrylic repair may be used as well for prosthetic hoof wall repair, as depicted in Figure 4.
Figure 4: Acrylic hoof wall repair
Prognosis is dependent on the response to treatment, as well as the effect of the original insult. Horses with poor hoof quality or primary laminitis tend to have reoccurrences of the disease. If initial response to treatment is good and proper environmental conditions exist, then the prognosis is better.
For any other questions associated with white line disease, please feel free to call New England Equine Medical & Surgical Center, or discuss management strategies with your local farrier.
Jordan E. Koivu, DVM
Elizabeth Taylor, DVM, DACVS - LA
"White Line Disease in Horses." Lameness in Horses: Merck Veterinary Manual. 1 Sept. 2015. Web. 10 Dec. 2015.
O'Grady, Stephen E. "Management of White Line Disease." Equine Podiatry. 2006. Web. 10 Dec. 2015.
Ross, Mike W., and Sue J. Dyson. "The Foot: Trauma to the Sole and Wall." Diagnosis and Management of Lameness in the Horse. 2nd ed. St. Louis, Mo.: Elsevier/Saunders, 2011. Print.
Recurrent Airway Obstruction (Heaves)
Horses are active and athletic animals that need to breathe efficiently and effectively to perform to their full potential. Respiratory problems can often go unnoticed, especially in the early stages, due to subtle or mild signs. The main signs of illness horse owners are advised to watch for such as fever, depression, or going off feed are not always present. Recurrent Airway Obstruction (RAO, "heaves") is a respiratory disease that is often overlooked in the early stages.
Recurrent airway obstruction is an allergic airway disease characterized by a chronic cough, nasal discharge, weight loss, and respiratory impairment that ranges from exercise intolerance to respiratory distress while at rest. Affected horses are typically middle-aged to older and do not show other signs of illness such as fever, depression, or pain. There have been two forms of RAO described: one is associated with exposure to irritants commonly encountered with confinement housing such as from dust, hay and bedding. The other is associated with molds growing on pastures in the summer. RAO is a common non-infectious inflammatory pulmonary disease that impacts the health and performance of horses across all equine disciplines.
Clinical signs occur in susceptible horses that are exposed to inhaled allergens from dust, mold spores and particles released by hay and bedding (straw bedding). When exposed to these allergens the horse's body responds by closing the airways (bronchoconstriction) and increasing bloodflow and cellular exudate resulting in inflammation and mucus production to trap the allergens and facilitate clearance. These mechanisms are meant to be protective of the airway but the result is detrimental to the horse's respiratory function. The bronchoconstriction and excess mucous increases the resistance to airflow especially during expiration. The increased expiratory pressure requires recruitment of the abdominal muscles to aid in exhalation. This results in well-developed abdominal muscles (hypertrophy of the external abdominal oblique muscle which gives the characteristic "heave line" appearance. The increased respiratory effort leads to decreased feed intake which results in weight loss. Horses with RAO tend to be exercise, heat, and humidity intolerant.
Continuous and prolonged irritation and inflammation of the airways increases their sensitivity resulting in exaggerated responses to the irritation, further exacerbating the problem. The respiratory tract's barrier defense is weakened and lead to secondary bacterial infections. Chronic infections lead to scarring of the lower airways further restricting the elasticity of the lung tissue and increasing the respiratory effort.
Recurrent airway obstruction is diagnosed based on clinical signs and by ruling out other causes of respiratory disease. A chronic cough, and nasal discharge without a fever are characteristic of RAO. An expiratory wheeze may be auscultated by your veterinarian on physical exam. Labwork typically shows a normal complete blood count, fibrinogen, and serum chemistry unless a secondary infection or concurrent disease is present. A Bronchoalveolar Lavage (BAL) is performed to evaluate cellular infiltrate, of which 35-50% of cells are expected to be neutrophils in horses with RAO. Spiral shaped mucous plugs from small airways (known as Curshmann's spirals) may also be seen. Transtracheal Wash (TTW) may be performed to obtain a sample for culture prior to a BAL in cases suspected of bacterial infection. Yellow exudate of increased viscosity may be visualized in the trachea via endoscopic exam. Radiographs may reveal over-expanded lung fields and peribronchial pattern of infiltrates while ruling out other lung disease (interstitial pneumonia, neoplasia, and abscess). Ultrasonographic evaluation of the lungs may also be used to assess the lungs and rule out concurrent disease.
Horses in respiratory distress need immediate veterinary intervention. Severe cases are treated with systemic corticosteroids and bronchodilators. While very effective, the potential complications (laminitis, adrenal suppression, decreased gastrointestinal motility, colic, etc) of these medications preclude their use as long-term therapies. Medical management with anti-inflammatories and inhaled bronchodilators are short term therapies to be used until the respiratory tract returns to a healthy state and environmental adjustments can be made.
The most important treatment and prevention of RAO is long-term environmental management. Affected horses should be kept on pasture at all times. A three sided run-in shelter may be provided for protection from inclement weather. Dry lots and enclosed confinement should be avoided. Prior to feeding, hay is to be closely inspected for signs of mold and soaked in water to remove dust and particulate allergens. Alternatively the horse's diet may be changed to a pelleted complete feed or fed bagged hay with high moisture content. Horses with the summer-pasture associated RAO respond best to stall confinement during the summer months when molds are growing on pastures. For horses that must be confined to a stall, stable management should be a priority. Hay should be stored in a separate building from where the horse is stabled, and never above the stall. Stalls should be well ventilated and cleaned daily, kept free of dust, cobwebs, and loose feed, and the horse should be removed during cleaning when the air concentration of particulate matter is highest. Additional measures such as using hypoallergenic bedding and watering arena footing can help to minimize dust and RAO irritation.
Early diagnosis and intervention is essential to prevent the disease from reaching an irreversible state. Recurrent airway obstruction is not curable, but it can be well managed through appropriate environmental changes. Horse owners and barn managers play an important role in the prevention and treatment of this disease.
Doctor Joslyn Mumford