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Epiphyseale necrose bij het paard

“Navicular disease” is the stuff of nightmares for ambitious riders: podotrochlosis (navicular inflammation, navicular disease) is one of the most common causes of chronic lameness in ridden horses. The symptoms of navicular disease vary. They can range from stumbling, rhythm problems, an uneven gait to clear lameness accompanied by head nodding. We’re here to tell you what navicular disease is, what causes this painful condition and how to best support an affected horse.

What is a horse’s navicular bone?

When they hear the word “navicular”, equestrians usually think of an inflammatory, degenerative disease of the horse’s hoof. However, “navicular” isn’t a disease, it is a complex deflection system for the deep digital flexor tendon in the sole area of the hoof, composed of the navicular bone, the deep digital flexor tendon and the navicular bursa.

The deep digital flexor tendon runs over the navicular bone to the back of the pedal bone.  The navicular mechanism ensures that with every movement, the tendon can slide smoothly over the navicular bursa and the cartilage of the navicular bone, between the short pastern bone and the pedal bone, as if over a roller. The bursa between the bones acts as a cushion and lubricant.

What happens in navicular disease?

Prolonged overloading can cause inflammation in any part of the perfectly balanced navicular system. Just the weight of the standing horse places a significant load on the flexor tendon, and the load is very much greater when pushing off for each stride in gallop! If the deep flexor tendon is subject to too much pressure, it reacts by becoming inflamed.

In more advanced cases, the tendon rubs on the cartilage of the navicular bone. The roughened cartilage tissue prevents the tendon from gliding over it smoothly, thus causing further damage. Disease and adhesions of the tendon around the navicular bursa can also lead to inflammatory processes there.

The affected navicular cartilage no longer receives a sufficient supply of nutrients. Consequences include destruction of the cartilage, as well as adhesions such as arthrosis of the coffin joint and decalcification processes in the bone tissue that can even lead to fracture of the navicular bone.

The condition generally effects both forelegs, often to differing degrees. The disease usually occurs for the first time in horses aged between 6 and 14. Provided that navicular disease does not become chronic and there are no indications of navicular degeneration yet, a full recovery is possible. However, once they have had one attack, horses remain susceptible.  

What symptoms does a horse with navicular disease show?

Navicular disease develops insidiously and is often identified too late. Inflammation in the region of the hoof causes pain, both when standing and when moving. The pain reduces the horse’s enjoyment of movement. The affected horse will typically avoid loading the heels and will increasingly move on its toes, which can often lead to stumbling. The horse’s gait loses its swing and becomes more cautious, leading many riders to push the horse on more energetically, putting it down to unwillingness or laziness.

In the more advanced stage, the horse begins to show lameness on one or both forelegs. Even for equestrian experts, the lameness is often difficult to assess because it does not always appear equally clearly. For instance, a horse may be lame at the start of a training session, but then moves normally once warmed up. Or the horse may appear sound on the straight, perhaps showing occasional irregularities, but is lame on corners or circles. The lameness can also move around, affecting the right foreleg at one time, then the left another time. Hard or deep surfaces often exacerbate the problem.

When standing, the affected horse often eases the load on the flexor tendon and stands with one or both forelegs alternately forward. Some horses stand with their knees slightly bent to avoid tension on the carpal joint which in turn places tension on the tendon. If the problem remains untreated, it can lead to deformity of the front feet. 

How is navicular disease diagnosed?

In cases of lameness with no clear cause, the veterinarian should be consulted as soon as possible. Diagnosis of navicular disease is not entirely easy, because the navicular mechanism consists of bones, tendons and soft tissue. If a lameness investigation in which the horse's gait is evaluated in walk, trot and on corners gives rise to suspicion of navicular disease, further investigations will be necessary.

  • Palpation of the hoof with farrier’s pincers in the area of the navicular bone can reveal the first indications of inflammatory processes and pain.
  • The wedge test used to be the preferred method to identify navicular disease. This is carried out by placing the horse’s front foot on a raised board for around 60 seconds to place greater load on the heel, and then immediately trotting away. Although clear lameness on trotting is an indication of navicular disease, it is not possible to make a definitive diagnosis using the wedge test.
  • X-rays can provide conclusive evidence of changes to the navicular bone. However, inflammation of the tendons and bursa will not be visible on an x-ray image.
  • Ultrasound examinations can reveal tendon damage and defects in the joint surface.
  • Nerve blocks can identify the painful area more precisely. These involve numbing the navicular nerve, which serves the lower part of the short pastern. If the horse is then sound in trot on the treated leg and more lame on the other leg, that can be considered as a clear sign of navicular disease.

Why can a horse's navicular bone become inflamed?

Whether a horse is susceptible to navicular disease can depend on many different factors, some of which are congenital, including

  • Hoof conformation such as contracted hoof, flat hooves with long toes, upright hooves with high heels
  • narrow or wide-toed hoof position
  • Limb conformation, especially upright pasterns and shoulders or long, sloping pasterns
  • Sex: Mares are less frequently affected than geldings
  • Breed: Warmbloods and Quarter horses are affected more often than Arabs or ponies In many Western horses, the hoof size is not in proportion to their body shape!
  • Gait: Riding horses were initially bred for their imposing gaits and elastic paces. Their impressive movements place a significant load on the limbs, with the heel area in particular subject to large forces.

Other factors, which are sometimes difficult to distinguish from a horse’s predisposition to develop navicular disease, can be both causes and triggers of the clinical picture:

  • Rearing flaws such as a lack of movement and rapid growth in young horses due to over-feeding, resulting in reduced bone quality and connective tissue weakness (cartilage, tendons, ligaments).
  • Lack of movement: If a horse spends most of its time in a stable, the hoof will struggle to adapt to the load of a rider in the short term. Riding is no substitute for continuous, relaxed movement!
  • Weak muscles
  • Shoeing or hoof trimming: Poor hoof correction or excessive intervals between trims can place extra stress on the navicular mechanism. For example, excessively long toes can exert a strong pull on the deep flexor tendon if the toe axis is broken. If constricting shoes are used with overly short or slim legs, the angle of the hoof wall can apply pressure to the navicular mechanism. 

Is navicular disease due to over- or under-feeding?

  • An overweight horse places additional load on its locomotor system. Plenty of movement ensures that a horse is at its ideal weight and improves circulation and nutrient supply to the hoof area.
  • Horses in training need more vitamins and minerals, which are often not provided by their basic feed! A balanced mineral feed can make up for any deficiencies. 

The use of horses by people plays a significant role. Navicular disease occurs most frequently in ridden horses, more rarely in driving horses and very rarely in young horses and breeding stock who are not ridden. One possible reason for this is that horses in the wild tend to travel in straight lines rather than in confined spaces and on curves. Wild horses also don’t jump high obstacles again and again. Their joints are not built for that. Wild horses do not suffer from navicular disease!

Is there a link between riding style and navicular disease?

Navicular disease is often called a “professional disease” of sports horses. That’s easy to prove if you imagine the load on the lower limbs of a showjumping horse as it lands after a jump. Or the high speeds at which an eventer travels across rough country. Or the tight turns and stops of a top Western reining horse or a polo pony.

Early backing and overloading young horses that are not fully grown, as is common practice in racing, for example, are often causes of subsequent navicular disease. 

However, it is not only horses in fast, athletic activities that are at high risk of navicular disease. Dressage horses that are pushed too early and too fast don’t have the muscle and power for difficult movements. They often show a lack of activity through the back and hindquarters, overloading the forequarters. 

Last, but not least, leisure horses that are just happy hackers are also affected. Training, muscle building and gymnastic exercises for our leisure partners are often neglected!

Groundwork with horses should not be confused with letting them run wild. Racing around a round pen, skidding, abrupt stops from high speeds and rapid changes of direction also places stresses on loose horses! 

How is navicular disease treated?

If the horse is in severe pain, the veterinarian will initially prescribe pain relief and anti-inflammatory medication. These can initially relieve the symptoms. However, this brings a risk that the horse - now pain-free - will overdo things itself!  Pain relief cannot cure navicular disease and is not a long-term solution, because these drugs will irritate the mucous membranes lining the horse's stomach.

Joint injections with anti-inflammatory drugs such as cortisone or substances that encourage cartilage growth such as hyaluronic acid, always carry the risk of infection. Treatments around the joint such as injections and flushes should be carried out in a veterinary clinic!

Glycosaminoglycans (GAG) can also be given in feed, but are only effective at high doses.

Compounds that influence bone remodelling can be used if the bone structure of the navicular bone and pedal bone has already been changed or weakened. The degree to which such treatment is useful is for the veterinarian to decide.

Shockwave therapy can be very helpful. Shockwaves are especially effective on changes to the navicular area directly beneath the navicular bone.

How does a neurectomy (“nerving”) work?

The nerves that supply the navicular region are severed in a small operation. The horse is then pain-free and no longer lame.

However, a neurectomy does carry some risks: it does not halt the degenerative process of navicular disease! The lack of sensation in the sole can lead to injuries, because the horse can stumble and even fall more frequently. Furthermore, it is especially important to take excellent care of the hoof, because the horse may no longer be aware of hoof disease. Horses that have undergone a neurectomy are not eligible to compete because the treatment falls under anti-doping measures.

These methods should only be used if other procedures are no longer helping. It is also essential to ensure that the none of the navicular structures are so damaged that there is a risk of complete destruction. As a consequence, many veterinarians advise against neurectomy.

Does a horse with navicular disease have to be shod?

Farriery plays a key role in the treatment of navicular disease. One current method is the use of an orthopaedic shoe with a shaped toe to make it easier for the horse to roll the foot. Raising the height of the heels with closed wedge plates can reduce pressure on the navicular area and tension on the flexor tendon. The shoe must be replaced approximately every six weeks.

This “misalignment” brings rapid improvements to lameness. However, new scientific studies clearly indicate that the change to the hoof mechanism leads to a reduction in blood flow to the hoof, which slows the healing process. Furthermore, it is expected that the sensory apparatus of the hoof will also be damaged, leading to discomfort that must be imagined to be similar to feet that have “gone to sleep” in ill-fitting shoes. 

Barefoot horses with navicular disease should be kept on a soft surface (sand, woodchip, etc.). If a herd gets on well and chasing can be ruled out, the horse may remain with the group in the open barn or pasture. In this case, however, close attention should be paid to see whether the horse is in pain or showing stress reactions, and appropriate action should be taken promptly! Plenty of peaceful movement ensures a good supply of nutrients to the navicular mechanism and encourages regeneration. Regular orthopaedic hoof trimming can help to improve the hoof mechanism.

Patience is called for!
The lameness will only improve after three months or so in a barefoot horse. It is not unusual for full recovery from navicular disease to take a year.

Can a horse with navicular disease be ridden?

Riding can be dangerous due to the frequency with which an affected horse stumbles. The horse should not be ridden all the while it is lame. Only when the horse is 100 % pain-free and moves in a good rhythm on hard ground can training start - slowly and carefully - again!

The horse’s sporting career is definitely over though, because there is a risk that it will suffer from navicular disease again. However, the horse and rider can still have a lot of fun as leisure partners!

Warning: some time off is urgently needed, even if the treatment means that the horse is no longer lame. Synthetic medications and orthopaedic shoes alleviate the symptoms, but not the cause of the disease. If damage to the deep flexor tendon is found, the horse will need a lengthy period of rest and should then be brought back into work very carefully. 

How can I support a horse with navicular disease?

  • Peaceful movement
    Horses with navicular disease must be able to move around as much as possible without overdoing things. 15 minutes of exercise in walk and trot will increase the circulation in the hoof by 15 %! Important: make sure that the horse does not overdo it. Avoid tight turns and hard, uneven ground!
  • Manual therapies such as osteopathy and craniosacral treatments have a positive effect on the general condition of the affected horse.
  • Herbs with anti-inflammatory and pain-relieving properties can promote the healing process and improve the horse's wellbeing without irritating its sensitive stomach:

What herbs can be used for hoof roll inflammation?

  • Devil’s Claw helps to support and relieve pain in degenerative diseases of the locomotor system.
  • Hemp nettle contains harpagoside, the same active ingredient as Devil’s Claw, and has an anti-inflammatory effect on joint disease.
  • Willow bark is one of nature’s painkillers. It is especially effective on joint disease and supports mobility.
  • Rosemary helps with joint pain and boosts the metabolism.
  • Dandelion helps the body to get rid of waste products and toxins 

Can I avoid navicular disease?

Regular hoof checks and corrective trimming
There’s not a horse in the world that has ideal, regular, textbook hooves. For horses with misalignments that could favour navicular disease, correction should be discussed with your farrier.

Do not allow your horse to become overweight
Feed rations should be reassessed at the latest when the horse's ribs are hard to find. Every excess pound is extra stress on tendons and joints. Warning: if the horse needs to lose weight and rations are reduced, ensure that the horse is still getting enough minerals!

Ensure that your horse gets enough free exercise
Movement keeps tendons and cartilage fit. The more your horse can move around freely, the better!

Always warm up properly
Whether you’re embarking on a training session in the school or a hack in the countryside, warming up is essential! Even horses kept in open barns need to warm up, to bring their muscles, tendons and joints up to “operating temperature”!

Ride your horse gently
Faster speeds on hard ground are a no-no for all horses. The hard impact doesn’t do the horse's tendons or hooves any good at all!

Strengthen the muscles of your horse’s hindquarters to reduce the load on the forehand,
If the horse is to remain healthy and fit for use for the long term, nothing but correct riding will do. The sense and purpose behind gymnastic dressage exercises is to straighten the horse, strengthen the muscles of its back and hindquarters to take more of the load, and to reduce the strain on the forehand.

Tip: For leisure horses, there are many exercises that, with a little imagination, can easily be incorporated while out hacking and which are also fun - riding uphill while stretching on a long rein, stepping over obstacles on the ground, changes of pace, etc.

The muscle metabolism of the horse can be well supported with natural means. Feed supplements high in vitamins and with an antioxidant effect, such as  rosehip, sea buckthorn and grapeseed oil are especially helpful for  building muscle. Spirulina seaweeds and linseed oil provide valuable amino acids that the horse needs to build muscle mass and to regenerate the muscles.

Sources

  • Christina Fritz, Souel Maleh: Zivilisationskrankheiten des Pferdes. Ganzheitliche Behandlung chronischer Krankheiten, Thieme, Stuttgart/New York, 2. Aufl. 2016
  • http://www.hufrollensyndrom.de/html/krankheitsprozess.html
  • Chris White: Podotrochlosis 101 | 24. Februar 2021 (=https://thehorse.com/184051/podotrochlosis-101/)
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