Laminitis and Founder;
What They Are and What Can Be Done.
by Dave Millwater, RMF
Founder... The very word can send a cold shiver down the spine of many a horseman. This misleading and potentially devastating condition has meant the end of many horses' careers; and sometimes even their lives. But just how does a bellyache or other stress cause a horse to be crippled? And what can be done about it?
To understand the answers to those question, one must have some basic knowledge of the anatomy of the equine foot. The hoof wall is the primary weight bearing structure of the foot. Within it is the PIII (Third Phalanx or Coffin Bone). The PIII is attached to the hoof wall by laminae. The laminae are special tissues which provide awesome attachment strength, but also allow the wall to grow down in relation to the bone.
The laminae are nourished by tiny blood capillaries. These capillaries normally provide a steady flow of oxygen and nutrients to the vital laminitic tissues.
As a precaution against frostbite, the circulatory system of the hoof has structures called AVAs (ArterioVenous Anastomoses) which can channel blood directly from the arteries into the veins, bypassing the fine capillaries. When the hoof becomes too cold, the AVAs open up and allow large amounts of hot blood to rush through the foot without being slowed by the high-resistance of the capillary network. This continues long enough to warm the foot up, but not so long as to starve the laminae.
Poisons ingested by the horse, toxins created within the horse after a feed binge, and a number of other systemic illnesses can create body chemistry imbalances that can cause the AVAs to malfunction. If the AVAs "lock" open for an extended period of time, the hoof will become hot from the rapid flow of blood within it, while the laminae will begin to die from the lack of blood actually reaching them. This is laminitis.
Because of the heat and high blood flow through the foot, laminitis has often been misunderstood. Even the word laminitis, which basically means inflammation of the laminae, reflects this misunderstanding. The problem is not the "fever" in the feet, but ischemia of the laminae. Normally, the laminar cells can withstand ischemia for quite some time, because the AVA's only open when the feet are very cold and oxygen demand is low. But, during laminitis, the AVAs stay open even when the feet have become hot, and the cells' need for oxygen is great while the supply of oxygen has been diverted.
If enough laminae are killed by laminitis to allow the PIII to loose its attachment to the hoof wall, and the bone begins to sink within the hoof, you have founder.
Because the laminae at the toes of the front feet are under the greatest mechanical stress and have comparatively precarious blood supply, most founder cases involve separation of the laminae in that area. In such cases the toe of the PIII sinks, causing that bone to rotate in relation to both the hoof wall and the pastern bones. The tip of the PIII moves down toward the sole of the foot, often causing bruising, hematoma, and the loss of the sole's concave shape. At the same time, the hoof wall at the toe is free from its moorings and begins to "peel" away from the PIII. The increasing gap between the wall and PIII is filled with scar horn material.
As if all this weren't bad enough; the separations in the foot's protective structure, bruising, loss of circulation, and necrosis all team up to make nasty abscesses in the hoof likely.
The burden of early treatment of laminitis falls primarily on the veterinarian. This treatment often involves dealing with the cause of the toxic reaction that instigated the laminitis and trying to promote capillary circulation through drugs. The vet may also administer pain killers, but most agree that these should be used only in the short term and within limits. The pain of laminitis tends to make horses stay still and off their feet, which is exactly what they need to do.
If the laminitis progresses into founder, the management burden shifts to the farrier.
The traditional approach for farrier management of founder is to lower the heels until the frog bears weight, then dress back the toes back as far as reasonably possible. This practice helps to shift the weightbearing away from the damaged toe to the heels, which are usually in better shape. Dressing back the toe reduces breakover stress and helps prevent the hoof wall at the toe from being pulled further away from the PIII.
Lowering the heels also brings the PIII closer to its normal position in relation to the ground and pastern bones. Although the frog does not need to bear weight in a normal hoof; in a foundered foot, the frog can provide valuable support.
Some farriers also cut a horizontal groove across the front of the hoof about an inch below the coronary band.
This provides a flex point to prevent stress from being transferred up the toe to peel back the laminae which are left intact in the upper part of the hoof and helps prevent the blood flow from being pinched off between the extensor process of the PIII and the hoof wall.
A shoeing remedy for founder which no-doubt owes part its popularity to the fact that it requires minimal skills to fabricate is the backwards shoe. Mechanically, this shoe acts as a rockered-toe eggbar. As such it provides the horse with extra posterior support to compensate for the great lack of anterior support and reduces the stress on the Deep Digital Flexor tendon which pulls on the underside of the PIII and contributes to rotation. The rockered-toe effect reduces breakover stress which is also a benefit to foundered feet.
Because the sole is already compromised at the toe by the sinking tip of the PIII, pressure to the sole applied by the shoe can have ugly results. Since the backwards shoe places no metal on the toe of the hoof, it can create no harmful sole pressure there. Unfortunately, it also does nothing to protect the delicate anterior sole from pressure or injury from the ground.
The backwards shoe also holds the frog up off the ground, depriving the PIII of the support in would have received from the ground through the frog. This makes the backwards shoe a less attractive approach when dealing with severe, actively sinking founder cases.
The backwards shoe can be a useful tool in the hands of a farrier who knows when to use it and how to apply it correctly. It can be worthless or even detrimental when used on foundered horses by cowboy shoers as a cure-all.
Burney Chapman, RJF, has expanded on the concept of supporting the PIII through the frog. Over the last decade and a half, he has popularized the use of the heart-bar shoe in the management of founder.
The heart-barshoe is used to create carefully applied pressure on the frog as the foot loads. This supports the PIII and helps prevent further rotation. Supporting the bone helps restore the circulation that was compromised by its sinking. This improved blood flow is needed for the laminae to regenerate.
The main drawback to the heart bar is that it must be applied properly. Pressure in the wrong places, or the wrong amount of pressure in the right places can do more harm than good. Mr. Chapman maintains that the reason many practitioners don't like the heart-bar is that they do not know how to apply it correctly.
While Mr. Chapman recommends the rigid heart-barshoe, some farriers like to apply his basic approach using flexible frog inserts.
Another management approach for founder has been popularized by farrier and veterinarian Ric Redden, RJF of the International Equine Podiatry Center. This method features dramatic raising of the heels using wedges and is based on the fact that the tension of the DDF tendon is an important contributing factor to the rotation of the PIII. The DDF runs down the back of the leg, passes under the navicular bone, and attaches to the underside of the PIII. Raising the heels reduces the pull of the DDF. As a salvage measure, Dr. Redden sometimes cuts the DDF altogether.
The problem with heel elevation as a founder remedy is that, while it temporarily reduces one force responsible for PIII rotation, it also focuses mechanical stress onto the toe, where the hoof is least able to stand it. Currently, Dr. Redden tends to use his wedge approach as a temporary measure before applying a shoe package that is designed to eliminate breakover stress and support the PIII from beneath.
All of the shoeing methods for founder outlined here have their own merits, and despite the fact that some of them seem diametrically opposed, they have each worked on given horses. It is up to the farrier to know which approach will work best based on his experience and the specifics of the case. In some cases, the farrier will combine aspects of each approach or change approaches as the progression of the founder dictates. This is why a knowledgeable farrier with the skills to apply his knowledge is of paramount value should your horse be stricken with laminitic founder.
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