By Timothy G. Eastman, DVM, DACVS, MPVM
Published in Bay Area Equestrian Network May 2006
The coffin bone is the primary bone within the horse’s foot (Figure 1). The hoof capsule encases this bone like a body in a coffin, hence the name coffin bone. The laminae within the foot are the soft tissue structures that firmly attach the coffin bone to the hoof wall. Laminitis, in its simplest terms, is inflammation of the laminae that attach the coffin bone to the hoof capsule. This inflammation decreases blood flow to the area of the laminar attachments. Local alterations in blood flow may be the result of a variety of systemic illnesses, such as grain overload, colic, retained placenta, etc. Oftentimes this disease is triggered by unknown causes. Whatever the source of the disease, laminitis usually causes crippling pain in horses and is potentially devastating to horse owners.
In some instances, the laminar attachments become so compromised that the coffin bone and hoof capsule actually separate from each other (Figure 2). If the normal pull of the deep digital flexor tendon exceeds the strength of the remaining laminar attachments, the bone may rotate downward away from the hoof wall. Veterinarians consider the disease chronic if rotation occurs or if the condition lasts for more than several days. Affected horses often appear as if they are “walking on eggshells”, hold their feet camped out in front, shift weight frequently, and are reluctant to turn.
Most treatments for laminitis focus on improving blood flow to the foot, alleviating the pain associated with this condition, halting disease progression, and reestablishing a functional relationship between the coffin bone and hoof wall. Veterinarians often use vaso-dilating agents such as acepromazine, isoxsuprine, pentoxyphyline, and nitroglycerin in hopes of improving blood flow. Phenylbutazone (Bute) commonly relieves pain and decreases inflammation in laminitic horses. A variety of recommended shoeing and trimming techniques attempt to decrease the amount of tension on the coffin bone and redistribute pressure on the hoof’s weight-bearing surfaces. If one shoeing method was consistently successful, it would dominate as the therapy of choice. However, as there are a multitude of ways to shoe a laminitic horse, people need to be open to the experience and expertise of their farrier and veterinarian. There are at least a dozen different shoeing programs that can be successful in horses with laminitis. A healthy relationship between your farrier and veterinarian is never more important.
In spite of extensive research, numerous approaches to treating horses with laminitis are sometimes frustrating and unrewarding. A multi-factorial condition, laminitis involves several body systems and prevents a single treatment regimen from becoming universally accepted or effective. Our understanding of this disease is expanding rapidly thanks to the efforts of researchers around the world. A complete overview of laminitis is beyond the scope of this paper but we would like to discuss several recent advances in the management of this disease.
Radiographs should always be taken of horses with laminitis. Not only are they useful in establishing the diagnosis, they also help determine the chances of a successful outcome and are very useful in guiding farriers through the therapeutic shoeing. Recently, many practices have coupled their radiographs with computer software to get very accurate representations of the angles of the bones of the feet (Figure 3). These programs are of tremendous value in assisting your farrier to determine how much toe and heel to remove, where the breakover should be, and potentially what type of shoe to apply. Radiographs also help identify whether or not “gas pockets” are present along the toe which could need to be addressed. These gas pockets are generated by necrotic tissue in the foot which oftentimes becomes infected. These are the horses that are frequently managed with a dorsal hoof wall resection which simply removes the dead tissue and prevents infection from becoming established.
Special radiographs that use a dye which is injected into the vasculature of the foot called venograms are useful in determining an individual horse’s prognosis and being done by more and more practices. Some specialists feel that if bloodflow to the toe is reduced by approximately 30% or more, the chances of survival are very slim. A venogram is obtained by placing a tourniquet around the ankle (for just a few minutes) and injecting a large volume of dye into a vessel below the tourniquet and quickly taking a radiograph (figure 4). The Christmas Tree like pattern of dye highlights the blood supply.
When cases of laminitis do not respond to conventional medical therapy and therapeutic shoeing, another alternative is to have a surgery called a Deep Digital Flexor Tenotomy performed. The surgery involves transecting the deep digital flexor tendon which is the main flexor tendon in the horse. While it sounds severe, this procedure relieves tension at the source of the pain and generally makes horses more comfortable in several days. The tendon ultimately reattaches in approximately 4 months which is frequently ample time for a qualified farrier to drastically improve the health of the foot. With this procedure, farriers can often accomplish improvement in the angles of laminitic horse’s feet that would have otherwise been impossible. This procedure can be done under anesthesia or in the standing patient and is a relatively low cost procedure with minimal risk in these patients.
The prognosis for horses with laminitis is very hard to predict. Severity of the radiographs doesn’t always correlate well with the amount of lameness seen clinically. The best way to guarantee the highest level of success is to assemble a team of experts including your farrier, veterinarian, and potentially trainer all communicating well and working towards the same common goal. While we are a long way off from a full understanding of the disease, advances in management of Laminitis are occurring at a steady pace.