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TREATING NAVICULAR DISEASE


Navicular Disease, now referred to as Navicular Syndrome or sometimes as Chronic Heel Lameness, or Caudal Heel Syndrome was first documented in 1752, by Jeremiah Bridges, a farrier, in his famous book “No Foot, No Horse” (published some 40 years before the opening of The Royal Veterinary College in London, England).

So what is this mysterious feared disease that still today sometimes has owners being advised to have their horses destroyed. If you look at any amount of vets or farriers text books you will be hard pressed to find two experts that agree on the exact science of the cause and effect of Navicular Disease. It has certainly kept book publishers busy for the last 260 years. The main problem has always been that researchers have been unable to fully reproduce Navicular Disease in experiments so this has led to endless speculation as to what causes the horses to experience this heel pain.

NAVICULAR ANATOMY
In order to grasp what the problem is it is necessary to know something of the anatomy of the horse’s hoof.
Navicular Disease usually occurs in the front feet. The navicular bone is a small bone held in place as part of the coffin joint by ligaments. Here it acts as a fulcrum to increase the leverage on the foot. The navicular bursa is located between the deep flexor tendon and the articular cartilage of the navicular bone. It’s job is to lubricate the surface of the bone so it can act like a pulley. The deep flexor tendon becomes wide and thin as it passes under the bursa and attaches to the coffin bone. It is in this complicated area of bones, tendons and ligaments that the horse experiences terrible heel pain so we call it Navicular Syndrome.

So while Navicular Disease does not directly shorten the life of a horse it does cause it to suffer this terrible heel pain. Over the years the farrier world has developed many ways to help relieve this pain and make the horse more comfortable. In order to understand the treatments you need to know the main theories regarding the causes of navicular disease. As long ago as 1752 Navicular Disease was attributed to “lack of exercise resulting in contraction of the foot” by Jeremiah Bridges. Many recent studies have only gone on to prove his theory accurate.

FIRST (and older) THEORY

Lack of blood circulation is thought to cause bone degeneration to the navicular bone. The theory is that when a horse is exercised the blood supply to the foot is good but if a horse is simply returned to a stable afterwards the blood supply is decreased and it is these disturbances in the blood circulation that can lead to this degenerative process.

It is also thought that concussion or compression forces coming through an excessively upright foot could cause this blood supply damage to the navicular bone.

Whatever the cause it is then believed that this damaged navicular bone causes inflammation to the deep flexor tendon and other ligaments surrounding the bone causing the horse this heel pain.

When researchers have reduced blood supply in horses feet to replicate this damage to the navicular bone they saw no changes which puts this theory in doubt. It has also long been known that many horses have degeneration of the navicular bone but do not experience navicular disease and similarly many horses with Navicular Disease show no damage to the navicular bone.

SECOND (more recent) THEORY

Dr Bowker of Michigan State University, a Veterinarian at the forefront of hoof studies, has done extensive studies on the back of the equine foot. Dr Bowker found that in foals the lateral cartilages that form the foundation of the rear half of the foot are less than 1/16th of an inch thick. These lateral cartilages develop as the foot grows by expansion, flexion and twisting of the hoof capsule. In his comparisons between domestic horses and feral horses he found that in adult feral horses these lateral cartilages were almost an inch thick and that these horses had a solid floor of cartilage between the frog corium and the digital cushion. In domesticated horses many foals are kept in small paddocks and on soft terrain. The result of this is that many adult domestic horses are found to have lateral cartilages as thin as 1/8th inch rather than the one inch found in feral horses. At the same time the development of the digital cushion in domestic foals falls behind either through being continually on soft terrain or through the tendency to neglect trimming foal hooves. Many are left to grow long upright heels reducing frog pressure throughout the growing foal’s life. This ends up in adulthood with a back foot too sensitive to be the “landing zone” it was designed to be so these horses start loading their toes first to avoid discomfort.


When a horse is said to be sensitive on rocky terrain people blame the soles but in fact almost every time they will shorten their stride, land on their toes and lean forward. They are avoiding landing on their sensitive frogs and heels. Dr Bowker found that the more horses try to move this way the weaker their hoof structures become. When a horse lands on its toes the weight of the horse then slams into the navicular bone as the heels crash down. This damages the impar ligament which supplies 80% of the blood supply to the navicular bone. Michigan State University also blame bone loss on the lack of natural pressure in the heel region from continued toe first landing. Dr Bowker is also finding navicular horses to commonly have 40-60% bone loss in the coffin bone as well.



A HEALTHY FROG & DIGITAL CUSHION


AN UNHEALTHY FROG & DIGITAL CUSHION

As to placing more doubts on the first theory a Veterinarian Pathologist called Dr James Rooney produced a book called ”The Lame Horse” with his findings from studies on thousands of dead horses. Dr Rooney found by simulating toe first landings in test machines with dead horse legs that the order of damage occurring around the navicular bone is

1/ Firstly the fibrocartilage surrounding the navicular bone is damaged.
2/ The second damage is to the fibrocartilages surrounding the deep flexor tendon.
3/ Thirdly the deep flexor tendon is damaged.
4/ Finally the navicular bone is damaged by the rough surface of the damaged deep flexor tendon.

Dr Rooney’s findings date back to at least 1974.

Although both these doctors have differences in their findings they do agree that Navicular Disease is a result of continued toe first landings by the foot and lack of use of the back of the foot.

TREATMENT BY SHOEING

Over hundreds of years there have been various treatments by farriers to “cure” navicular disease. You will still see many of these used  today as they are still taught in many farrier schools.

Most shoes have been designed with the idea of easing the deep flexor tendon by easing its work. This has involved high heels, rolled toes, rocker toes. From experience I can say that these shoeing treatments relating to the first theory above can help a horse be comfortable for months or years but eventually they do fail and the horse will be even worse than before. At this point these horses were usually destroyed.

WEDGES

Horses have been shod with wedge shaped pads between the hoof and the shoe in order to raise the angle of the foot. Previously it was thought to be great practice to raise the back part of the hoof with a wedge or calks so as to relax the flexor tendons and so reduce inflammation. In practice this has long been considered an outdated theory. By trying to raise the hoof in this way the pressure on the heels is increased, the heels will be completely pushed in or away resulting in them no longer performing their function. Treating a horse like this only makes the Navicular Disease worse.



CALKS


A second example of how horses have been treated for Navicular Disease with shoes is with fixed calks. These are horseshoes with a heightened band of iron/steel welded on the branches. The idea is to again raise the back of the foot to relax the flexor tendons. Using a shoe with small calks did not work as the calks just sink into the ground.

Because this shoe adds too much weight to the back of the hoof one of the side effects it has is that it gives a release of kinetic energy when the hoof moves forward. Because the weighted branches have more kinetic energy than the toe part, when the hoof is set down this creates a shock to the inflamed area which is even more uncomfortable for the horse. Some horseshoe manufacturers still produce an aluminum version of this as a “navicular shoe” which does get away from the weight issues but it is still putting the same pressure on the heels as the wedges do.


HOOF PADS

A third example of treatment would be a horseshoe with a hoof pad between the hoof and the shoe. This has the effect of evenly distributing the ground pressure over the whole hoof and engaging the frog (which the previous two examples do not do). The space between the pad and the hoof is usually filled with fast setting silicone which gives a good even support over the hoof. The main disadvantage of a horseshoe with a hoof pad attached is the weight it places on the foot

EGG BAR SHOES

For a fourth example of treatment for navicular disease there is the use of the Egg Bar Shoe. These shoes are, as the name implies, egg shaped and when they are applied the bar should lie in a vertical line with the bar not  touching the frogs. When the back of the bar touches the ground first followed by the hoof it is light walking in ski boots for the horse. These shoes create a large amount of kinetic energy when the horse moves this way and there is no indications or proof that these shoes either solve or improve the condition.

BAR SHOES

Another shoeing treatment is the use of Bar Shoes. This is a broad, long shoe with a thin metal bar at the back to immobilize the shoe’s movement. This lack of movement helps to equally load the hooves when then the feet are turning. They are lighter than the Egg Bar Shoes and give good support to protect the sensitive heel area but nowadays there are better alternatives.



EPONA SHOES (SYNTHETICS)

These are plastic bar horseshoes of material designed to reduce concussion through the hoof and limb. They are much lighter than metal shoes and, importantly for horses that are in a lot of pain, they can be glued into place rather than requiring nailing. They support and protect the heels while engaging the frog and building the digital cushion. By far the most successful form of treatment if trimming alone is not successful.

TREATMENT BY TRIMMING

Again going back to the theories relating to the cause of this heel pain. When heels get long and under run, as they are in these horses, the weight bearing area of the heels is moved forward until it is directly below the navicular bone rather than behind it as it should be in healthy horses. Added to contracted heels in these horses and you find this area is put subject to more active pressure than it is designed for. With this unnatural pressure damaging the bone surely it is not the bone loss that is causing the horse pain, but the pressure creating the bone loss that is causing the pain.

There are very successful ways of dealing with Navicular Disease by careful trimming. The horse’s sole should be left alone while the heels are gradually trimmed down to increase pressure on the frogs. This isn’t a “how to trim” article so I won’t go into details but this has to be done at the correct pace for the horse. Too slow and no difference is made, too fast and the horse will be sensitive in the back of the foot and continue to walk on his toes. This job is what separates the good hoof trimmers from the hackers.
If the horse is still very uncomfortable following a trim the use of hoofboots will protect the feet until they are less sensitive. I use Easyboot Epics routinely but any boots would work. The Easyboots have a range of pads to put in the boots that can make these horses comfortable when nothing else will.

When the frog begins to be engaged again it will start to pack into a dense callous and become the weight-bearing surface it should be. Only by stopping the toe first landing and making the horse comfortable to place it’s heel down first can you hope to improve these horses.
Properly trimmed the frogs and digital cushions will toughen up and the horse will get more comfortable. Any damage to the navicular bone will remain but the horse probably won’t know about it. The horse won’t be the same as a horse that hasn’t gone through this but it should be sound and usable. In much the same way as we humans collect injuries and pains through our lives, horses do as well. Get them comfortable enough and they live with the minor aches and pains.

FINALLY

There are no miracle cures for this problem and every horse seems to respond differently to trimming or shoeing. The repair process can be very much trial and error. I have seen some horses go sound from a first trim and others take months to improve.

However the bottom line is that if Dr Bowker’s theories are to be believed then Navicular Disease is preventable. By allowing foals and young horses lots of exercise and time on dry rough ground at an early stage to develop their frogs and digital cushions we could be preventing these toe first landing horses altogether. Watch that your young horses are landing heel first.



 

(Note that no information given on this website should be considered
a substitute for consulting your veterinarian or farrier)

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