Degenerative Suspensory Ligament Desmitis of the Horse
By Dr. Garrett Metcalf
The suspensory ligament is a vital component of the limb of a horse to produce normal locomotion and support. The suspensory ligament is a common area of concern in performance horses of various disciplines and can be single handedly the cause of lameness or performance issues. This article is going to look at a specific degenerative disease of the suspensory ligament and what horses are at risk for this disease.
DSLD or degenerative suspensory ligament desmitis was first discovered in the early 1980’s in Peruvian Paso horses. The name has been changed because the suspensory ligament is not the only organ affected from the disease but the suspensory is ultimately the biggest issue. The newer name, ESPA or equine systemic proteoglycan accumulation, is more correct because other ligaments and tissues are affected by this disease. In this article we will only focus on the suspensory ligament. The most commonly affected breeds are Peruvian Paso, Paso Fino, Morgan, Saddlebred, Warmblood, Paints, American Quarter Horse, and Thoroughbred breeds. The age of onset of the disease is variable among breeds but it is more common to be seen in middle age to older horses. However it has been documented in horses as young as one year of age. The disease generally will have a slow insidious onset that can go undiagnosed for months or years depending on the horses work and discipline.
A horse that begins to show early signs of DSLD may have a vague lameness issue that is difficult to isolate and they most likely will resolve with a period of rest. As the horse returns to moderate level of work the lameness will return. This scenario may go on for several months or more before the discovery of the DSLD is made. The first indication of DSLD is often pain isolated in the suspensory branches or fetlock region when a flexion test is performed. Horses with DSLD will also have a “dropped” fetlock appearance because the suspensory is the main supporting structure of the fetlock joint. DSLD can affect the hind limbs, forelimbs or all limbs at the same time. A unique sign of DSLD is that not just one limb is affected but rather bilaterally affecting the limbs, meaning it will either affect either both forelimbs or hind limbs at the same time. It is my experience that the hind limbs are more commonly affected compared to the forelimbs. Horses will often have enlargement of the fetlock region and increased joint fluid or wind puffs. Horses will often have a straight hock or post legged hind limb appearance. Horses will often shift weight frequently in an effort to get relief from the discomfort and this can be confused with other lameness issues or foot related pain.
Diagnosis of DSLD is often made by clinical signs, breed and ultrasound findings. Ultrasound imaging of the suspensory ligaments will often show diffuse enlargement of the suspensory body and branches. The suspensory ligament will have a poor heterogeneous fiber pattern with periligamentious soft issue thickening from scar tissue deposition and edema or fluid within the tissue. Radiographs of the lower limb may reveal abnormal bone changes in the sesamoid bones behind the fetlock joints and even osteoarthritis of the pastern and or fetlock joints. A definitive diagnosis can be made from a biopsy of a ligament in the neck called the nuchal ligament, but is not often performed because of the invasiveness of the biopsy.
Treatment is very limited and it is mostly geared towards protection of further damage by prolonged rest. Pain management is also important to attempt to keep the horse as comfortable as possible. Different shoeing techniques can be used with marginal success. In early cases of DSLD, a suspensory shoe that helps engage more work from the deep digital flexor tendon can help elevate the fetlock and offer more protection to the suspensory ligament. The devastating thing about this disease is that there is no cure and there are hardly any good options to slow the progression of the disease. DSLD carries a poor prognosis when the diagnosis is made in any breed of horse or any discipline. Although some cases can be managed better than others, it often progresses to the point of debilitating pain and discomfort to the point of humane euthanasia especially in the Peruvian Paso breed.
Read more in the February 2023 issue of Oklahoma Farm & Ranch.
Guttural Pouch Diseases of Horses
The guttural pouches of horses may not be very well known to most horse owners. These bilaterally paired pouches are located below the base of the skull, below the ears and extend into the throat latch region. The pouches purpose is not fully understood, but some theories is that they reduce the weight of the skull or have a blood cooling function to reduce the temperature of the arterial blood going to the brain. The guttural pouches can be plagued with a multitude of issues that are difficult to treat or can be life threatening to the horse. Other species contain guttural pouches such as some bats, American Forest mouse and Hyraxe.
The anatomy of the guttural pouches is complex and houses various important anatomic structures. The guttural pouches are an auditory tube diverticulum that is analogous to human Eustachian tubes but much larger. The volume of the guttural pouches can be up to 400-600 milliliters of air. The guttural pouches contain large arteries, nerves, the bones of the inner ear, muscle tissue and part of the hyoid apparatus that connects the skull to the larynx. The opening of the guttural pouches is deep in the nasopharynx through the slights call the pharyngeal ostium, which can only be accessed with an endoscope passed up the nose. The difficulty of accessing this area makes treatment of these diseases challenging at best. The guttural pouch is the only location in the horse that allows direct visualization of the arteries and nerves. The main arteries that are present in the guttural pouch are the maxillary artery and the internal and external carotid arteries that provide all the blood to the skull. The nerves in the guttural pouch are cranial nerves that exit directly from the brain or brain stem that innervate critical structures that control breathing, swallowing, chewing and ocular functions of the skull.
Read more in the April issue of Oklahoma Farm & Ranch.
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.
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