Therapeutic Shoeing Part 2: Hardware and Healing
By Christy Corp-Minamiji, DVM • Aug 19, 2015 • Article #28437
Photo: The Horse Staff
Egg bars, heart bars, wedges, pads, trailers, caulks, wooden shoes, rocker shoes, natural balance shoes--the list of contraptions that can be applied to or removed from the bottom of a horse's foot is extensive. How can an owner hope to wade through the myriad shoeing options when even veterinarians and farriers can't seem to reach consensus? According to Andrew Parks, MA, Vet MB, MRCVS, Dipl. ACVS, the Olive K. Britt & Paul E. Hoffman professor of Large Animal Medicine at the University of Georgia's College of Veterinary Medicine, the method used to shoe a horse is less important than developing a set of goals based on sound biomechanical principles.
As discussed in Part 1, all farriery alters the forces upon the foot and must be viewed in light of those forces. The three main forces are:
- Ground reaction force (GRF)—the upward force of the ground on the hoof;
- The force of the horse's weight transmitted downward through the limb; and
- The upward pull of the deep digital flexor tendon (DDFT).
Changes in length, angle, or weight-bearing of any foot structure alters these forces. Considering these basics, we can examine some common foot pathologies and therapy options.
I'd Like to Try This Pair in Navy ...
Wilton, Calif., farrier Al Moates likes to quote a colleague, saying, "The best therapeutic shoeing is a flat, balanced set of shoes." His quote points back to the beginning of this discussion: Any shoe--plain, bar, or otherwise--must be set upon a properly trimmed foot to be beneficial.
The basic horseshoe is a steel shoe that is hammered in shape to conform to the bottom of the foot where the hoof wall meets the ground. Typically, the shoe is nailed to the wall, although clips and adhesives can be used to decrease the number of nails necessary and to offer additional security for keeping the shoe on the foot. An array of other shoe types and modifications are available based on this basic shoe design, including:
Bar shoes These close the gap at the base of the heels and take several forms:
- Straight bar: A straight bar connects the heels of the shoe, with the goal of stabilizing the downward pressure of the foot and distributing weight more evenly across the foot. A straight bar also extends the foot's ground surface.
- Egg bar: A roughly symmetrical oval, the egg bar's heel portion often extends beyond the base of the heel bulbs and must be placed with caution as excessive protrusion behind the heels acts as a lever and, when used with pads, can crush the foot's soft tissue structures.
- Heart bar: An inverted V mimicking the outline of the frog connects the heels of the shoe. While a heart bar is sometimes touted as supporting the foot's bony column, Parks believes the increased ground-surface contact in the back half of the foot is likely the reason for this shoe's beneficial effects. However, for a heart bar shoe to be effective at transferring some of the load from the wall to the soft tissues, "the foot must have a good frog," says Stephen O'Grady, DVM, MRCVS, professional farrier and owner of Northern Virginia Equine, in Marshall.
Aluminum shoes This metal is lighter than steel and is thought by some to decrease concussion. Aluminum shoes come in multiple forms from plain to egg bar.
Wedges shift the forces upon the foot. Wedging can be achieved with degree pads, rails applied to the shoe, or by increasing the thickness of the shoe's heel branch.
- A toe wedge extends the coffin joints and, to a lesser degree, the pastern joints.
- Medial (along the inner aspect of the foot) or lateral wedges (along the outer) will alter the load bearing of the foot toward the thicker part of the wedge.
- One of the most common wedges--the heel wedge--raises the heels, decreasing the tension in the DDFT by moving the coffin joint slightly forward.
If the heel structures are already damaged (e.g., the horse has developed underrun heels) or if the wedges are not applied properly, the increased pressure on the heels from the wedge will prevent new hoof wall growth and damage the heel further. In these cases the heel is raised at the cost of the back of the foot.
Natural balance shoes A square-toed, wide-webbed shoe, the natural balance shoe was developed based on imprints of feral horses' feet. The boxy shape builds the breakover (when the heel has lifted but the toe remains in contact with the ground) into the shoe. As with any shoe type, a natural balance shoe should be applied to a foot that is properly trimmed for the individual horse's conformation and use.
Wooden shoes Strictly therapeutic, wooden shoes are cut from plywood. The bottom of the shoe can be beveled to meet the veterinarian's specifications; the shoe is then screwed to the hoof wall just as a standard shoe is nailed on. According to O'Grady, a wooden shoe's bevel eases breakover, decreasing the forces upon the lamellae--which suspend the coffin bone within the hoof capsule--in any direction.
My Horse Has _____. What Shoe Will Fix Him?
If you haven't seen it coming, this is where we tell you there is no shoeing magic bullet. "You're never going to put shoes on a horse and (say), 'Wow! He's a new horse,' " says O'Grady. Most disease states arise over time, and time also is required for treatment.
"Disease or pain is a function of excess stress," says O'Grady. "With farriery you can address the stresses or forces on a given section of the foot." Bearing in mind the forces discussed in Part 1, we can examine various conditions from a "goals" mindset--as Parks mentioned earlier.
Low heels A combination of genetics, hoof conformation, footing, and inappropriate farriery can lead to a horse having low heels, says O'Grady. The term can mean two things:
Palmar (rear) heel pain (navicular disease) The advent of MRI has expanded our understanding of the structures within the hoof capsule and the causes of heel pain. It's become evident that what used to be referred to as "navicular syndrome" can involve more than just the navicular bone (the wedge-shaped bone that articulates the coffin bone and short pastern). According to O'Grady, first the veterinarian should make the best possible diagnosis based on imaging and lameness exams. The second step is analyzing the foot (i.e., "What does the hoof capsule look like? What do I have to work with?"). While conventional approaches to treating palmar heel pain often involve using a bar shoe or elevating the heel to reduce DDFT tension over the navicular bone, in the case of the aforementioned crushed or underrun heels pads and heavy shoes such as egg bars might worsen damage. In fact, sometimes the answer might be no shoe at all.
Quarter cracks/sheared heels "You don't find quarter cracks without sheared heels," says O'Grady. Moates agrees: "If you have a nice, flat, balanced foot that lands correctly, you don't get (quarter cracks) that much." Rather, he sees quarter cracks as "an indication that something else is wrong."
Quarter cracks result from uneven application of force to the foot when it lands on the ground. Says O'Grady, "Sheared heels appear to develop as an adaption-distortion of the hoof capsule as a consequence of limb conformation that results in an abnormal strike and loading pattern of the foot on the ground."1 In other words, sheared heels are a distortion of the hoof in which one heel bulb becomes elevated toward the pastern relative to the other. The true quarter cracks in these horses begin at the coronary band, travel toward the ground, and extend through the hoof wall into the sensitive tissues.
"Various materials and techniques exist for stabilizing and repairing hoof cracks, but none will be successful in the case of spontaneous quarter cracks unless the cause of the hoof wall defect is determined and addressed through basic farriery," he continues. "Farriery is directed toward unloading the hoof wall and decreasing the forces on the displaced side of the foot where the quarter crack originates."1
While O'Grady believes a straight bar shoe works well to stabilize a quarter crack, remember that lowering the displaced heel and maintaining an appropriate trim are the keys to tackling this condition.
Laminitis This inflammation of the lamellae is a complex disease, the details of which are beyond this discussion (related fact sheet). However, basic principles apply to shoeing the laminitic horse. O'Grady stresses that veterinarians/farriers assess a laminitic horse's foot conformation. Goals for these patients include:
- Treating the cause of the laminitis through medical and/or dietary therapy;
- Decreasing the moment (forces upon) of the coffin joint;
- Transferring the load from the lamellae to the back of the foot; and
- Decreasing the tension of the DDFT and its pull on the coffin bone.
These goals can be achieved using a number of methods, including (but are not limited to) removing shoes and placing horse in a conforming footing such as sand or pea gravel or applying a reverse shoe, one of various bar shoes, or a wooden shoe. Regardless of shoeing technique, a trim aimed at meeting the above goals is key to managing laminitis.
Resolving any hoof condition requires communication between owner, farrier, and veterinarian. Equally important is understanding the principles behind the chosen therapy. "Goals matter most," says Parks. "The method you choose that matches the goal doesn't matter as much as applying it well." After all, five farriers and five veterinarians might give you 10 answers; the key to success is each participant's comfort with and understanding of the principles behind the method used.