© Rob Kalb
Based upon my previous and ongoing shoeing experience, combined with lots of observation and study, I've formulated a theory about shoeing horses with navicular. Please keep in mind that this is just my view based upon what I know now, and that could change a year from now. But by shoeing horses accordingly, I've had good results.
There are three conformation types contributing to navicular syndrome. They are as follows:
Upright Pasterns
In the horse with upright pasterns, the job of the navicular bone has been changed from its normal function. No longer does it act as a fulcrum for the deep flexor tendon. It also has the additional increased function of bearing weight, due to the angle of the joint between P2 and P3. The angle should be normally close to 0 degrees. Instead of the pastern and fetlock joint flexing towards the ground, as with a normal hoof pastern axis, the fetlock flexes very little. This drives the navicular bone out of its normal position.
The result is a stressing of the suspensory ligaments of the navicular bone and the newly discovered chondrocoronary ligaments. Over time, calcium spurs start to form at the medial and lateral aspects of the navicular bone. When these spurs are forced into sensitive tissue by the action of the pastern, the result is pain.
I feel that no shoe known to man can correct this problem. The only way to make the horse comfortable is to perform a neurectomy. After surgery, I like to shoe the horse with as close to an unbroken hoof-pastern axis as possible. Use a plain light or rim shoe with a rockered toe. I'll use pads if the sole of the hoof is unusually tough or hard, in order to retain moisture in hopes of improving the shock absorption properties of the hoof. I've been shoeing a horse like this for two years with no hint of unsoundness. Early diagnosis and treatment is always a contributing factor in determining the prognosis and outcome of any case.
Shallow Heels
A low shallow heel on a hoof also means a thin digital cushion, causing a decrease in the hoof's ability to absorb concussion. This condition also puts the navicular bone closer to the ground. Hooves of this type also have very little concavity, which adds to the problem. As a result of the continuous concussive forces received by the navicular bone, it starts to remodel. Remember: Bones react to stress and shock the same way metal does. Bend a wire hanger back and forth repeatedly, and it breaks. Bend it, then let it rest a while and the bend is harder than the unbent portion of the hanger. Do this repeatedly - bend, rest, bend, rest - the bend becomes very hard to straighten.
In the horse, if the bone is stressed almost to the point of failure, the body says, "Hey, wait a minute, we need more bone here." It then sets up the facilities to do so. In the case of the navicular bone, I feel that in some horses, the stress is too constant, or frequent. The remodeling process accelerates almost out of control, resulting in poor quality boney tissue with sharp points and edges that inflict pain during the bearing phase of limb motion.
To quote Dr. Dane Frasier, DVM, endurance rider, "The horse's body responds to stress by adapting. If stress is placed upon a tissue group repeatedly before the end of the adaptation period of that tissue group, the result is failure of that tissue group. For hard tissue - bone, tendon, and ligament - the adaptation period is 7 to 10 days." By this time you're probably saying, "I thought he was going to talk about shoeing navicular horses, not wire hangers and some endurance rider." Trust me it all comes together.
Remember, in the type of conformation we're talking about here, the hoof-pastern axis is usually broken back, the heels are low or nonexistent, and there is little or no concavity to the hoof. Also, I've noticed the hoof is disproportionately longer than it is wide, adding pressure from the deep flexor tendon during the breakover phase of the leg, to further complicate matters.
All of these factors directly relate to an increase in pressure and shock to the navicular bone, I feel, stressing it to the point of failure. To shoe this horse correctly, we need to eliminate or reduce these forces to the best of our ability. For shoe type, depending on whether it is one or both hooves, with this particular conformation, I choose from the following:
Also, I like to RADICALLY ROCKER THE TOE! Not 15 degrees as mentioned in the Butler book, but about 45 degrees from the first nail holes forward. There is usually a lot of toe that can be dropped back on this type of hoof. Watch the horse move to see where the hoof breaks over. Is it straight over the front or off to the side? If it's off to the side, rocker the shoe off to the side as well. Rasp the toe down to match the rocker on the shoe, then finish seating the toe hot. Yes, burn it in. This shoe will increase hoof angle, and facilitate breakover.
For pads, I like to use thick leather with just enough silicone to fill the commisures, or Hoofprints Impak pads with the same packing. If the heels are really low and the frog is flat and thin when measured from ground surface to the inside of hoof (you know when you look at it, and push on it), I will use a steel egg bar shoe brought back to the bulbs of the heel, toe rockered 15 to 20 degrees, and a 2- or 3-degree wedge pad conservatively packed so as not to apply excessive pressure to frog and sole of hoof.
I rarely use the Tennessee navicular bar shoe. I usually use it only when both feet are affected. For more hoof angle, use wedge pads. If the toe is farther from the fetlock joint than I'd like, I rocker it.
I don't set the shoe back to the white line and rasp the hoofwall down to the shoe. This compromises the structural integrity of the hoof capsule at the toe. By rockering the toe, I can significantly decrease the breakover point, still thin the hoof wall to about half its original thickness, and retain a structurally sound hoof capsule.
The above-mentioned suggestions are designed to achieve the following:
One leg longer than the other (compressive-type navicular syndrome)
This condition is fairly easy to fix, if it hasn't progressed too far. I just stand the horse on a flat, level, hard surface, get both front hooves side by side, use a tape measure and measure from the ground to a point on the inside of the knee that is an easily recognizable reference point. Are the two measurements the same? If not, I look at the feet. Does one have a high heel and the other a low heel? If so, the one with the high heel is usually the short one.
Next I check the distance of the shoulder blade from the top of the wither. Are they equal on both sides? I trim the high heeled hoof and try to get a hoof angle that will come close to matching the other hoof. It is usually the low-heeled hoof that is afflicted with navicular syndrome, because it is carrying more of the horse than it was designed to do. I find that most farriers will put a wedge pad on the low-heeled hoof. This is not good, as it further increases the load on an already-overloaded leg. I've worked on horses that were shod this way for quite some time. The result was a hoof that avulsed the hoof wall from the second or third nail holes back to the bulbs of the heel, all the way to the hairline. The heel bulbs dropped over the back of the shoe almost to the ground. This is what happens when you lengthen a leg that is already longer than it should be.
To beat all, no one can figure out why the horse still won't go sound. We've got him in a bar shoe and wedge pad on that navicular foot and can't figure it out. Maybe we should probably just put him down.
But let's try to save him, instead. I trim the low heeled hoof, leaving as much heel as possible, (that is if there's any still there). I measure the toe length and try to get it the same on both feet. For shoes, I use a shoe that fits the low-heeled hoof the best. The high-heeled hoof is usually smaller in size. I trim the heels to fit the smaller hoof. With both feet trimmed, now I check the difference in leg length. On horses with up to about a 1 inch difference, I'll use a 1/4 inch or 3/8 inch lift on the short leg. I can leave it as a full pad or cut the center out and make a rim pad.
Before applying the shoes, I measure from the end of the toe on the high-heeled hoof to the center of the fetlock joint. I check this measurement with that of the other hoof. If on the low-heeled hoof the distance is greater, I rocker the toe to move the breakover point to that of the high-heeled foot. This means that if you measured 4 inches from the center of fetlock to toe on the high-heeled foot and 4 3/4 inches on the low-heeled foot, rocker the shoe and hoof 3/4 of an inch back from the toe end. If I need to go further, I make sure I have enough foot to do it.
This will get both hooves breaking over at the same distance from the center of the fetlock joint. The result will be an easing of the pressure from the deep flexor tendon on the afflicted navicular bone. The lift on the short leg will get it carrying more of the load. This arrangement should build up the shoulder muscles in the short leg, making both legs the same length fairly quickly. It usually works in one to three shoeings. Remember not to get carried away with the thickness of your lift pads. If the knees are not the same distance from the ground on the first shoeing, that's OK.
I hope this information is taken as a guide to help look at these horses in a different light. I have shared it with you because it works for me most of the time. Not every procedure works the same on every horse. It is my hope that some of you other farriers will try it, add to it or detract from it, as you so wish. But most of all, I hope that by using these guidelines, and adding your own ideas and intuitive decisions, you are able to restore a comfortable and useful life to horses that were otherwise thought to be hopelessly lame. Feel free to post comments, questions and disagreements to the "Navicular" bulletin board in the "Farriers Helping Farriers" section of this site.
Return to the Farriery Articles listing page.
