By Lauren Lamb, DVM
Navicular ‘disease’ is a condition that affects the navicular bone, navicular bursa, deep digital flexor tendon and/or the associated ligaments attached to the navicular bone. Navicular disease, navicular syndrome, caudal heel pain syndrome in the horse, or insert some other name, are all terms used to describe the same condition, pain in the heel region of a horse. For the purposes of this article, navicular disease will be the term used to describe pain from the heel region of a horse. Navicular region will refer to the navicular bone, associated ligaments, navicular bursa and deep digital flexor tendon.
Before we can talk about navicular disease, we need to step back and review the normal anatomy. The navicular bone is located behind the coffin joint, within the hoof capsule. The navicular bone articulates (forms a joint) with the coffin bone and short pastern bone, which are located on the front side of the navicular bone.
The deep digital flexor tendon runs on the back side of the navicular bone. The navicular bursa lies between the navicular bone and the deep digital flexor tendon. The bursa is a fluid filled sac that functions as a shock absorber and a lubricant for the deep digital flexor as it passes around the navicular bone. Several other small ligaments help hold the navicular bone in place. These small ligaments are extremely important and frequently contribute to the horse’s pain.
The exact cause of navicular disease is unknown. Several potential causes for the disease have been proposed. Each theory revolves around some sort of trauma to the navicular bone and its associated ligaments, tendons or bursa. Another common theory is interference with the blood supply to the navicular bone. Navicular disease rarely develops in the hind limbs. It is predominantly seen in the front feet of a horse seven to 14 years of age. Thoroughbreds, Quarter Horses and Warmbloods are more commonly affected than other breeds. However, any breed of horse can develop navicular disease.
Lameness is the primary clinical sign seen in a horse with navicular disease. Navicular disease usually affects both front feet, but typically a horse will be more lame in the left or right leg. The lameness may only be seen with the leg on the inside of a small circle or when exercising on hard ground. The lameness will get worse with exercise and improve with rest. Typically Phenylbutazone (Bute) will improve the lameness to some degree.
Diagnosis can be challenging for a horse with navicular disease. The process of isolating the lameness to the heel region of a horse is easy and straight forward. This can be done with a temporary nerve block that will desensitize the horse’s heel. Once the lameness is localized to the heel, the real challenge of trying to identify the exact cause of heel pain begins.
Radiographs can be taken to evaluate the coffin joint, navicular bone and angles of the horse’s foot. The radiograph will provide little information regarding the soft tissue (ligaments and tendons) surrounding the navicular bone. Ultrasonography is typically used to image soft tissue structures in a horse; however, the location of the navicular bone within the hoof capsule makes ultrasound imaging challenging. The best way to image the navicular region is to use an MRI. The MRI provides the best quality imaging of both soft tissue and bone structures. The hoof wall does not influence the quality of image obtained with an MRI.
Pick up the June issue to learn more!
Splint Bone Injuries in the Horse
By Dr. Garret Metcalf, DVM
Splint bone issue in horses is a common problem in various ages and disciplines. These injuries can be caused by excessive work in young horses to traumatic injuries. The splint bones do play an important role in the stability of the joints that they help make up at knee or hock level. These various types of injuries will be discussed in this article as well as treatments.
The splint bones are small bones that are intimately attached to inside and outside of the cannon bone. The splint bone is divided into sections to understand which section is injured. At the top you have the head of the splint, then a mid-body section and at the bottom the button of the splint. The head of the splint bones make up part of the carpus (knee) in the forelimb and in the hind limbs the hock. There is a fair amount of research that has demonstrated the role the splint bones play in the stability of these joints. A study conducted at Colorado State College of Veterinary Medicine noted that when larger portions of the splint bone were removed rotational stability was significantly impacted within the carpus including other directional forces affected.
Diagnosing splint bone injuries are rather straight forward with radiographs, but some cases ultrasound is also helpful. Some of the bone or callus formation that occurs around these splint bone injuries can compress on the suspensory ligament leading to chronic pain and lameness issues.
Splints that are popped are referring to injuries that generally occur to the younger population of horses entering training and work. Younger horses generally develop these injuries on the inside forelimb splints and they can be rather painful leading to loss of training time. The popping of a splint is the tearing of a ligament that holds the splint bone to the cannon bone called the interosseous ligament. When the ligament is torn bleeding can occur and disruption of the periosteum of the bones causing a callus or firm boney lump. These splints are more prone to injury because the medial or inside splint on the forelimb bears direct load with the second carpal bone at the head of the splint bone. This puts direct force on the splint bone where other splint bones share the load of the adjacent carpal or hock bones with the cannon bone.
Popped splint bones are often rather painful, have notable swelling associated near the splint bone and will have heat present. When palpated or squeezed a moderate amount of pain will be elicited.
Treatments of these popped splints are often rest, systemic anti-inflammatory drugs and local anti-inflammatory treatments. Acute inflammation from a splint injury can be soothed with ice or cold therapies and bandaging. Also alternative therapies such as cold laser therapy, MagnaWave or shockwave can be incorporated to the treatment plan. In some more extreme cases surgical removal of the bone callus is necessary to prevent the callus from compressing the suspensory ligament.
Splint Bone Fractures
Fractures of a splint bone can occur at any level or in any one of the splint bones but there are some that are more commonly fractured. The lowest or distal one-third of the splint bone is commonly broken in the forelimbs. These fractures can be occasionally to forelimb suspensory related issues. The suspensory is has a small ligament attachment to the button of the splint bone and whenever the lower limb is extended heavily this can put bending forces on the lower part of the splint bones leading to fractures. In the hind limb the outside or lateral splint bone is the most commonly fractured splint bone. This splint bone is often fractured from kicking injuries. Whenever two horses don’t get along back up to each other and fire some kicks, this splint is often the one that gets broken. These injuries are particularly more problematic because of the open wounds that are heavily contaminated with manure, hair and dirt, plus injuries to flexor tendons as well.
Fractured splints near the head of the splint are also very problematic injuries that can be career ending or life threatening at times for horses. These fractures can involve the joints of the carpus or hock leading to septic arthritis, severe lameness and possibly serious instability of the corresponding joint. The rule of thumb for equine veterinaries that are familiar with surgically removing damaged or fractured splint bone is the two-thirds one –third rule. The rule is the lower two-thirds can be safely removed and try to never remove the upper one-third if at all possible. Cases of complete splint bone removal can lead to chronic lameness or worse, catastrophic joint dislocation when the horse tries to get back up from anesthesia. Instead of removal of the fractured upper one-third of the splint, the fracture can in some cases be repaired with plates and screws to maintain a stable upper part of the splint bone.
Other smaller traumatic injuries that can occur to splint bones often come from interference injuries or the horses own feet hitting the inner splint bones when working. These injuries can be avoided rather easily with splint boots placed on the lower limbs whenever working. Some lower limb boots can provide some support to the fetlock and suspensory to avoid distal splint bone fractures but overall these are not going to be very protective.
Some splint bone injuries are rather simple and common problems that a lot of horse owners are familiar with addressing. When it comes to the more serious traumatic fractures and wounds related to splint injuries it is best to contact a veterinarian and get these examined.
No Foot, No Horse
By Dr. Garrett Metcalf, DVM
There is a wise old saying no foot no horse and that is absolutely true. Horses of all breed, discipline and size must have good healthy feet or they will suffer poor performance, chronic pain or worse succumb to diseases of the foot. There are several medical conditions that require surgical treatment within the hoof wall of the horse and this article will highlight the most common conditions that require surgical treatment and specialty farrier care.
Foot Abscesses –
Foot abscesses are a very common issue that nearly every horse may experience at some point in their lifetime. Abscesses are often minor issues that can be easily corrected by a farrier or veterinarian getting access to the abscess to allow drainage but they can be rather debilitating and sometimes rather serious. Abscesses in general are localized pockets of infection that found its way into the sole or white line of the foot. These abscesses often form because there is some structural abnormality of the foot, trauma that led to bleeding under the sole or improper hoof care that has led to abnormal forces being applied to the foot and of course the old hot nail. For example trimming of the foot without relieving enough sole pressure can lead to overloading the sole and in turn sole bruising setting up for an abscess. Other common abnormalities of the foot that leads to abscessation are laminitis and club feet. These two conditions can cause tearing and stretching of the white line and allow bacteria plus moisture to enter deeper into the foot which in some cases can further destabilize an already unhealthy foot, leading to a life threatening situation. Deep abscess that go untreated for days or weeks can continue to invade and dissect through tissue planes leading to larger abscesses. These large abscess sometimes require surgical intervention to keep them from spreading and to eliminate the abscess all together.
Pedal Bone Osteitis
Pedal bone or the coffin bone is a very unique bone compared to others in the horse. The coffin bone is a rather porous bone that has intimate attachment to the foot capsule and sole. The bone and the hoof tissue has a very high amount of blood supply rightly so because of the vast amount of metabolic rate energy it uses to keep the foot supplied with nutrients. Whenever the hoof is diseased or compromised from laminitis or infection the blood supply can be compromised as well spelling disaster. The disaster that can ensue from these conditions is an infected portion of the coffin bone or sequestration of bone. Bone sequestrums are when bone lacks blood supply and is also infected by bacteria that thrive off of dead tissue. Bone sequestrums are generally rather treatable conditions because once removed the bone can heal but the coffin bone is not the same as other bones in the horse. The coffin bone lacks an outer soft tissue coating called periosteum. Periosteum is a very robust membrane outside of almost all bones that provide blood supply and support healing with progenitor cells and stem cells. The uniqueness of the coffin bone without this important layer leads to poor healing, a more delicate blood supply and makes is more prone to infectious insults.
Treatment of an infected piece of the coffin bone requires aggressive steps in order to prevent spread and destruction of the rest of the coffin bone. Further spread into the coffin bone can lead to further damage to the blood supply to the bone and hoof as well as weakening the bone to the point of fracture under the weight of the horse. Aggressive surgical debridement or removal of infected tissue and bone is the first required step to reduce the amount of infection present in the foot. Secondly is aggressive antibiotic therapy using local delivery methods and systemic routes of administration. Local antibiotic delivery is by means of antibiotic beads, pastes or ointments and by means of regional limb perfusions. Regional limb perfusions are 20-30 minute treatments where antibiotics are delivered to the affected limb via blood vessels in that limb. The antibiotic is held in the limb by a tourniquet above the application site to allow higher concentration of the drug to enter the target tissue or region of the limb. Lastly is proper support of the remaining hoof while still maintaining access to the infected areas to allow local treatment. This step cannot be overlooked and requires the work of a talented farrier to make it possible.
Quittor is a chronic deep infection within one of the collateral cartilages of the coffin bone. The collateral cartilages are attached on both wings of the coffin bone and are often referred to on x-ray films as side bone. Lacerations, puncture wounds, trauma and abscesses of the foot can lead to infection of the collateral cartilage. To most people quittor doesn’t sound like a big deal and seems like it would be easily addressed with a few days of antibiotics but that is not the case. This infection deep in the foot can be like a smoldering fire that cannot be put out until the infected cartilage is removed. The diagnosis is usually straight forward because there is often a draining tract with swelling, heat and proud flesh centered over one of the collateral cartilages. The difficulty lies in finding and removing all of the infected tissue not to mention that you have to go through the hoof wall to get there. A hoof wall resection or a window cut in the side of the foot is often needed to access the infected tissue, allow drainage and local treatment at the same time. Quittor can be rather difficult and sometimes require multiple surgeries in order to get the infection cleared up. After the hoof wall resection is made often a specialized shoe will be needed to help protect and keep the foot stable until the hoof grows out the defect in the hoof wall.
Keratoma is a benign tumor like growth that arises from the hoof wall or laminar tissue of the foot called keratin. Keratin is what makes up our hair and nails. This growth continues to expand between the foot wall and the coffin bone leading to pressure necrosis and damage to the coffin bone. This abnormal keratin tissue is usually located at the toe region of the foot and is thought to be triggered by trauma to the hoof tissue. The most common signs of a keratoma are reoccurring foot abscesses in the same location and same foot, plus lameness that are localized to the foot. X-ray, CT and MRI can be used to diagnose keratoma formation within the foot. Often the keratoma is well formed enough to be seen with x-ray but sometimes advance imaging is necessary to make the diagnosis.
The only treatment and cure for a keratoma is surgical removal through the hoof wall. This requires a hoof wall resection with either an oscillating saw or drill bit to removal the hoof wall without damaging the coffin bone. A keratoma has an often distinct appearance by this off white crumbly type tissue that is often easily removed from the surrounding healthy hoof wall. After surgical removal a specialized shoe is needed to protect the foot and allow access to treatment of the surgical site to prevent infection.
Coffin Bone Fractures –
There are many different patterns or ways that a coffin bone can be fracture and some are more serious than others. To keep it simpler we break them down into articular or non-articular meaning do they enter the coffin joint or do they not. Non-articular coffin joint fractures generally are much less serious and can be healed without major surgery. Often times non-articular fractures are stabilized with a special shoe and casting tape placed around the foot to make the hoof itself the “splint” for the coffin bone nestled inside the hoof wall.
Articular fractures of the coffin bone are a much more serious problem because of the damage that is done to the coffin joint. A fracture into any joint is a serious threat to the health of the joint and requires surgical reconstruction as soon as possible to keep the joint from developing crippling arthritis. The trouble again with any surgery on the foot is that the bone is inside the foot making it difficult to access. There are techniques to place screws into the coffin bone through small hoof wall resections to allow stabilization of coffin bone fractures. It does require the right fracture pattern and location to make this surgical treatment a plausible option.
A street nail surgery is used to treatment of deep penetrating injuries that occur at the frog or sole that leads to infection of the bottom of the coffin bone, navicular bone and closely related surrounding soft tissue structures. Street nail procedures are often needed when a metal object such as a nail or screw penetrates and infects the one of the vital structures of the bottom of the foot. This window allows flushing of the synovial structures and removal of damaged/infected tissue. This procedure success is greatly improved with the use of an arthroscopic camera placed in the navicular bursa or coffin joint depending on what area the puncture wound involves. The arthroscope allows better visualization and more thorough flushing of debris and infection out of these tight spaces. Again this surgery cannot be successful with the application of a special shoed called a hospital treatment plate shoe that allows access to the bottom of the foot while keeping the foot clean and protected.
As you can see there is a pretty clear pattern to these hoof conditions: infection and the need for specialized farrier care. In order to be successful in treating these conditions the veterinary surgeon and farrier must work hand in hand to provide the best care for the horse. Although performing surgery on the foot of a horse is challenging and sometimes limited, it is often possible to have successful outcomes with a variety of different conditions.
Equine Laminitis – No Foot No Horse
Laminitis is probably by far the most devastating disease that a horse and horse owner will ever face. The definition of laminitis is nothing more than inflammation of the lamina or the tissue of the foot, but that does not describe the devastating pain and struggle that a horse faces with this disease. There are many sources of laminitis or foundering in horses. I will cover some of the most common causes, ways to avoid these causes and treatments.
The foot is an amazing organ for the horse and it is amazingly resilient but at the same time very fragile. The equid foot has to endure nearly constant loads of just daily locomotion but also endure very high levels of load during events such as racing, jumping and pulling. The tissue that holds the foot attached to the coffin bone is only a few millimeters thick but is amazingly strong. The tissue looks like Velcro under a microscope and is very rigid but also at the same time allows the foot to flex, grow and expand. The metabolic energy and blood flow rate that feet require to with stand this load is incredibly high as well. The blood flow to the very farthest part of the horse is complex and important when addressing laminitis which will be discussed later.
- Grain overload or carbohydrate overload
Consumption of a large amount of grain can lead to gastrointestinal disruption leading to founder. A horse that breaks into the feed shed and consumes large amounts is the most common scenario that is seen. These horses need to have as much grain removed from their stomach as soon as possible with a stomach tube and then products such as activated charcoal administered to help bind toxins that may be produced from bacteria dying off from the high grain load in the gut.
- Metabolic conditions – PPID (Cushings) and EMS (Equine Metabolic Syndrome)
Horses with cushings have high levels of glucocorticoids circulating in their blood leading to disruptions of the lamina along with other body systems. These abnormally high glucocorticoids are caused by an abnormality with the pituitary gland in the brain. This can be corrected when diagnosed with medication.
The EMS horses have high levels of insulin which has been found experimentally to induce laminitis. Horses that are obese and get very little exercise are at risk of EMS. EMS is reversible and prevented by managing diet more closely, routine exercise and preventing access to lush green pastures.
- Lush green grass (Grass Founder) – commonly seen in overweight EMS horses
Similarly, horses with underling EMS can found on lush green growing grass because of the high sugar content in these grasses. In the spring with good grains and plenty of sunshine grass can grow rapidly. This rapid growth phase of grass produces larger amounts of sugars in the blades of the grass during photosynthesis. It has been discovered that during peak sunlight is when the highest sugar content is found in the grass because of higher amounts of photosynthesis occurring in the grass blades.
- Endotoxemia – Caused by severe illness such as sepsis, colic, pneumonia
Horses that have serious bacterial infections or acute colitis can absorb endotoxins released by the dead bacteria. Horses are extremely sensitive to endotoxins and these toxins are called LPS (lipopolysaccharides) that make up part of the bacteria cell wall. When a large amount bacteria are killed off with antibiotics or disruptions in the horses gut these toxins are absorbed causing lots of problems for the horse.
- Overloading weight – injuries that cause the horse to bear more weight on another limb
Overbearing weight on other limbs from an injury to another limb can cause contralateral limb laminitis. Just by shear overloading force breaks down another foot. This can occur when a major injury occurs to a limb forcing more weight onto another because of pain. This is seen commonly with fractures, serious soft tissue injuries and neurologic conditions. This is what led to the death of Barbaro, the famous thoroughbred race horse that fractured his leg during the Preakness.
- Black Walnut – Shavings containing black walnut can induce laminitis
The species of tree can be very toxic to horses and must never be used as bedding or shavings that will come in contact with horses. It has been estimated that shavings containing as little as 5% black walnut can be toxin to horses. Some research has even thought that contact along can be deadly.
Diagnosing laminitis is rather straight forward. Examination of the horses gait at a walk or trot will indicate lameness. Most horses in acute founder will be severely lame at a walk and will be shifting weight back to the hind limbs in order to move or change directions when ask to ambulate. Horses will have an increased pulse in the arteries near the feet called a digital pulse. This pulsation of blood is similar to the throbbing sensation that we feel have an acute injury to a finger or limb and is quit notable in acute laminitis. Heat can also be noted around the coronary bands and hoof wall.
Radiographs or x-rays are used determine the severity of laminitis by measuring the separation of the coffin bone from the hoof wall. Venograms are also used to identify the blood flow damage to the foot using contrast dies injected into the digital veins while a tourniquet is applied above the foot. The contrast highlights the blood vessels so they can be seen with x-ray.
Treatment of Laminitis
First of the underlying cause of the laminitis must be eliminated or managed in order to get the laminitis under control or the battle will be very difficult. For example if a horse with EMS is not put on a serious diet and their weight managed you will be fighting a losing battle. Secondly a veterinarian and a farrier team are going to be needed to help manage the horse’s feet to prevent further laminar damage and provide the best possible foot support needed. Veterinarians must provide pain management, systemic care or treatment of the underlying illness and administer other medications that can benefit the horse in order to eliminate laminitis. Farrier’s have the daunting task of providing support of 1,000 pound or more horse that has feet sometimes the size of tea cups. The goal for farriers is to provide the proper support with various different methods across the sole of the foot at the same time eliminating stress and forces that inherently designed into the horse’s foot. Care for the horse’s feet is very critical and requires a skilled team to provide the best care. Lastly is that you have to be in it to win it. Short cuts and half hearted attempts are usually not very fruitful when it comes to dealing with laminitis. Below is a list of treatments used to treat laminitis.
- Medication or surgery to correct the underlying cause
- Cryotherapy or icing of the lower limbs and feet
- Systemic anti-inflammatory drugs and pain management
- General health care such as a good diet, deep beading, management of other illnesses and supportive care
- Corrective foot care
- Surgical intervention with tenotomies (cutting the deep digital flexor tendon)
- Slings (rarely available and only in extreme cases)
Laminitis or founder can be very challenging to correct or manage. It is not uncommon to humanely euthanize horses for acute or chronic causes of founder. These horses are often losing weight, unable to get up and ambulate well enough to eat or drink frequently enough. Often it is important to have a discussion of quality of life on behalf of the horse and do what is necessary so the horse is not suffering. These are always difficult decisions but they are necessary and always good to have these with your veterinarian and farrier that are caring for the horse.
Read more about your horse’s health in the latest issue of Oklahoma Farm & Ranch magazine.
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