About this article.
Navicular syndrome or navicular disease is a condition that has affected horses throughout the ages. For this reason, numerous studies have been carried out on the subject and it would appear that the conclusions are more or less cut and dried; the experts seem to be of more or less unanimous opinion on treatment and prospects.
This article attempts to shed light on a different treatment and thus also radically revised prospects.
The information presented in the video by Dr Jim Schumacher of the College of Veterinary Medicine at the University of Tennessee, forms the basis of the facts and figures given in this article.
What is Navicular Syndrome?
Since the days of the war horse, men have needed to explain ‘adequately’ why their horses were not able to go into battle. Simply being ‘off colour’ or ‘limping a bit’ would not have been sufficient reason for the sergeant at arms who was tasked with recording the (non-) availability of his army. As a consequence, various evocative but non-descriptive terms have entered the equine language. Colic is typically one of them: a vet might use the term colic, but not professionally–it doesn’t mean anything. It is a vague term that means the horse has a problem with its digestive system; it could be an ulcer in the stomach, it could be gastroenteritis, it could be a twisted colon…
Navicular syndrome, on the other hand, has led something of a charmed life as a description. To the point that even researchers and veterinary surgeons believe that it truly exists, albeit that they have given it all sorts of fancy names nowadays: podotrochlosis, podotrochleitis, podotrochlear syndrome, navicular arthritis or even navicular disease. And specialists will analyse x-ray photographs of potentially ‘navicular’ horses and proclaim they see wear here, growth there and deformation elsewhere.
In actual fact, there is no consensual definition of navicular disease; it is simply considered to be ‘chronic lameness of the forelimb associated with pain arising from the navicular apparatus’. You will note that the pain ‘arises from the navicular apparatus’ but is not necessarily directly associated with it! In fact, navicular syndrome has become something of a joke in veterinary practice, being described as a last-resort diagnosis. Just what it was in the military days–we don’t know what it is or what causes it, but we’ll give it an interesting name, nevertheless…
The theorised causes are legion; the video by Schumacher gives a reasonable overview of many of these theories.
How is it treated?
Current thinking about the treatment of navicular syndrome is little changed from that of more than sixty years ago. There is still a whole progression of treatments that veterinary surgeons and farriers go through in the process of dealing with navicular syndrome, most of which are old hat and just one or two are a little more modern.
Taking cue from the Schumacher video, which covers the subject quite adequately from the traditional veterinary/farriery point of view, we see the following commentary:
- THERE IS NO CURE, ONLY MANAGEMENT !
- Not helpful although most horses temporarily improve somewhat with rest (a positive viewpoint – ed.)
- Corrective shoeing (according to Schumacher ‘…one of the more important things for management’)
Schumacher makes the observation that it is very rarely seen in the hind limbs and where it is, it is also present in the forelimbs.
Correcting under-run heels and the medio-lateral balance of the hoof are recommended to encourage the horse to land heel first rather than toe first. After this, all forms of corrective shoeing are essentially aimed at reducing the force exerted on the deep digital flexor tendon by the navicular bone. The hoof angle is increased by between 2˚ and 4˚ – in one experiment, it was claimed that the force exerted by the DDFT was reduced by 24% when the heels were raised by 6%. This is achieved in various ways by means of special shoes, shims, rocker bars, egg bars… (There is a vast array of kit available to the farrier in pursuit of treating navicular syndrome –ed.)
Again, according to general opinion and observation, improvement after corrective trimming and shoeing may take weeks. But if the horse already has well-conformed feet, then little can be achieved with shoeing changes.
This is noted as not being useful if the horse is to compete and will be subjected to drugs tests. Otherwise, the systemic administration of anti-inflammatory drugs, such as phenylbutazone (1g – 2g daily) is recommended.
- Warfarin is also a possibility but is noted to be dangerous and there is no good proof of efficacy.
- Isoxsuprine increases blood flow by reducing vascular musculature [sic] and may improve drainage from the medullary spaces reducing intramedullary pressure. It has anti-inflammatory and hæmorheologic properties but seems only to be effective in horses with no or only mild radiographic changes.
- Pentoxyfylline is another hæmorheologic drug but without proved efficacy (Schumacher poses the question whether navicular syndrome is ischæmic or not).
- Injecting corticosteroids into the digital inter-phalangeal (DIP) joint is considered a ‘quick fix’ but may need repeating.
Repetition is likely to be effective but for increasingly shorter periods of time. The average duration of efficacy is 4.6 months, according to one study.
Temporary improvement is sometimes followed by severe lameness!
- Injection of corticosteroids into the navicular bursa would appear more effective than into the DIP joint but the same (contra-)indications apply.
- Sarapin can be injected around the palmar digital nerves but despite claims of being effective for 2-3 months, it would appear to have little effect at all.
- Polysulphated glycosaminoglycans is supposed to protect cartilage and was shown in one double blind study in 1993 to be effective.
- Distention of the navicular bursa by introduction of 6ml of a ‘therapeutic mixture’. Efficacy is not known although in one study 29% of bursæ ruptured at 5ml.
- Tiludronate (Tildren®) can be used to regulate the bone metabolism correcting remodelling changes…with the main improvement between 2 and 6 months. After 6 months, treatment appears to lose efficacy.
- Shockwave therapy was shown in one study to be effective but a second study showed the opposite.
- Sectioning of the proximal suspensory ligaments of the navicular bone showed in one study (again, in 1993) 76% of 118 horses to be sound at 6 months but only 43% at three years. And in all probability, the efficacy is as a result of (accidentally) cutting the nerves to the NB–these traverse the ligaments.
- Palmar-digital neurectomy with associated complications: progression of injury; failure to alleviate lameness; sensations returning within 6 months; painful neuroma etc. not to mention exclusion by a.o. the FEI from competition. There are techniques to prevent re-innervation. Efficacy of the procedure is 12 to 18 months in 65-70% of horses.
We can conclude from the figures given above that treatment in general is only of limited duration, 6 months in many cases, 12-18 months in the case of neurectomy and not much more than 3 years at best.
From the viewpoint of this article, it is worth examining the statements made with regard to the current treatment of navicular syndrome before proceeding to the alternatives.
Schumacher states it also being seen in the hind limbs–this statement is rather subject to question; there is little if any material reference to hindlimb navicular syndrome and these are probably examples of the ‘last resort of the diagnostically destitute‘!
- There is no cure, only management : this statement is very clear; nobody within the conventional veterinary/farriery world has managed to come up with a definitive cure, only repetitive and progressive treatments that, in the end, have little or no effect.
- Correcting under-run heels and the medio-lateral balance of the hoof are recommended to encourage the horse to land heel first rather than toe first : under-run heels are the signature of many a farrier who claims (as will many of his well convinced clients) that the horse has ‘low heels’ and this must be minimised; medio-lateral balance is only something that is a problem with shod horses because there is
- no possibility for the horse to find its correct balance itself through natural wear
- the farrier can never determine the correct balance since the foot is in a static situation when he looks at it but dynamic once it is on the ground
- Increasing the hoof angle by 2˚-4˚ may appear to reduce the force exerted on the DDFT but as a result, the horse will compensate by flexing the deep digital flexor muscles and the dorsal muscles leading to pain elsewhere. Furthermore, the DDFT is intended to be under tension–this means there will be no whiplash effect upon impact with the ground; reducing the force/tension makes the DDFT more susceptible to damage (particularly at the interfaces with the coffin bone and the DDFM).
That improvement…may take weeks will probably not come as a surprise however, the corollary is interesting: …if the horse has well-conformed feet, then little can be achieved with shoeing changes. This raises at least two questions:
- Why were the feet allowed to get into such a poor state in the first place–this is clearly a case of extremely poor farriery. The regular farrier’s excuse of a horse having ‘poor feet’ is nothing more than that; an excuse.
- What are well-conformed feet? We can readily draw the conclusion that the origins of the problem are quite probably foot related since corrective shoeing ‘[is] one of the more important things for management.’ This would tend to indicate that the apparently well-conformed foot is not well-conformed at all…
The first comment relating to medical therapy defines the position of the horse in the relationship: he is not a partner, a friend, a respected animal; he is a machine to be rolled out and put to work whether on the point of mechanical failure or not. It should be clear, a horse that has a significant injury should not be ridden and should certainly not be entered into competition.
The second point is the use of phenylbutazone (or any other anti-inflammatory for that matter). Particularly phenylbutazone is used almost with impunity as if it was the safest and most effective drug in the world, a wonder drug to be prescribed for all ills. IT IS NOT. Phenylbutazone is banned from human application–in some countries for more than forty years–because of its dangerous side effects, particularly in combination with other, seemingly harmless, drugs. Phenylbutazone, like most drugs, releases toxins into the body and particularly in the case of the less mobile horse, this can lead to drug-induced laminitis. (It should be noted that at least in France, phenylbutazone is indicated solely for chronic laminitis. Use of the drug for other pathologies is at the risk of the prescribing veterinary surgeon.)
Shockwave therapy as a surgical solution is highly questionable; as demonstrated, although one study claimed it to be effective, a second study showed exactly the opposite to be true. Shockwave therapy remains questionable for many pathologies where it is applied.
Sectioning the suspensory ligaments may have two effects: one is as stated by Schumacher, that the nerves to the navicular bone are cut at the same time causing essentially a nerve block; the second is the displacement of the navicular bone caused by cutting the ligaments–this would have a similar effect to the further jacking up of the heels of the horse altering the forces and point of contact between the DDFT and the NB. An effect that, like the shoes, is only temporary.
Palmar-digital neurectomy is quite simply the most ridiculous ‘solution’ possible. The horse is injured; by removing the feeling, the horse cannot feel that it is injured and so allows the rider to continue as if nothing was the matter. The horse is now in a position to injure itself even further without even knowing it and quite possibly irreversibly. This is like seeing the oil warning light flash on in the car; you go to the garage and the mechanic disconnects the light. The problem is still there, only you are no longer warned about it…
Is this the state of equestrianism today???
A Different Strategy
First of all, it must be realised straight away that time is the key. In this respect, we agree wholeheartedly with Dr Schumacher that once treatment has begun, it can take weeks before a real improvement is seen. Where we do differ, is the reason for this delay.
It is not sufficient to simply say that navicular syndrome is prevalent in thoroughbreds, quarter horses, warmbloods and standardbreds; it is most prevalent where these horses are shod. Very rarely do we come across cases of navicular syndrome in unshod horses–although it is not completely unknown. The reason for this is straightforward. An adequately trimmed hoof will, through natural wear, be able to find its own natural balance in all planes without the ineffective intervention of man. Farriers and those barefoot ‘specialists’ that have essentially been trained by a former farrier (as have most) will spin yarns about ‘balancing the hoof’. This is absolutely impossible since the hoof in function is a dynamic structure; when the trimmer takes the hoof in hand, he is looking at the static hoof–the two cannot be compared. Furthermore, if we leave the 1/16 inch (1.6mm!) of wall protruding below the sole as advocated by one internationally renowned trimmer, the first few hundred metres of tarmac will wear that down to nothing!
This naturally found balance in the hoof is the key to not suffering from navicular syndrome. The tendo-muscular chain of the horse–and any other animal for that matter–is very finely tuned. A minor deviation here or there is enough to put the whole structure out of kilter. We see a similar situation with weightlifters: it takes little more than a piece of paper between the teeth to make it almost impossible for them to lift a heavy weight. This is not to say that unshod horses are immune: Schumacher talks of the under-run heel in the shod horse but, quite clearly, a poorly trimmed hoof leading to under-run heels or overly high heels, will result in a similar conformation to the affected shod horse. The only advantage our unshod horse has, is that the severe concussion suffered by iron hitting ground, is absent. Don’t let anyone fool you, iron does not cushion the blow, it amplifies it. In order for iron to be flexible enough to cushion impact, it must either be in the form of a spring, or it must be heated to between 600˚ and 800˚C.
Our approach is very simple:
- remove the shoes–first the rears, then, a few days later, the fronts
- progressively lower the heels and hoof wall
- encourage the owner to encourage the horse to walk every day on hard surfaces
- start with ten minutes
- increase by 5-10 minutes a day
- if the horse has a relapse, do not stop but drop back to what he can do (always at least 5 minutes) and build up again
- don’t ride him until he is comfortable with his newfound feet
In fact, to treat the navicular syndrome, all that is needed is to remove all the shoes and trim the feet back thoroughly–the four points listed above have very little to do with navicular syndrome but are actually our protocol for removing horseshoes.
Why this protocol then? Quite simply, as already stated, almost all horses suffering from navicular syndrome, are shod. Recovery from navicular syndrome is almost instantaneous, as will be explained in a moment, but recovery from shoeing can take a long time. Despite anything the farrier might tell you, hot-shoeing is neither painless nor is it harmless. The iron is heated to ±600˚C to make it malleable and then ‘fitted’ to the hoof; at this point, it is still at somewhere between 450˚ and 550˚C. The hoof is only a few millimetres thick and underneath are the living tissues of the foot. This heat travels through the hoof and cauterises the internal structures of the hoof. Repeating this process at regular intervals interrupts any regenerative process and recauterises everything. Once we take the shoes off for good, the regenerative process now has a chance to take place without interruption. Unfortunately, this results quite frequently in the repetitive appearance of abscesses. Farriers and many vets will put this abscessing down to the fact that the horse is barefoot; this is quite simply ignorance at work–it is not the fact that the horse is now barefoot but rather the fact that it has been shod that is causing the abscessing. Additionally, by lowering the heels, there is an increase in tension on the deep digital flexor muscle and the horse may initally suffer muscular discomfort from this change.
Why does it work?
As already explained above, the tendo-muscular chain of the horse is very finely tuned. We can compare it with a suspension bridge: if all the cables are in place and under the right tension, the bridge will carry the weight of traffic passing over it with no problem (within its construction limits). If we break or alter the tension in just one of the supporting cables, the bridge will not collapse, but it will suffer additional stresses on the other cables and also on the road deck. Likewise with the tendons of the horse, and in this particular case, the deep digital flexor tendon (DDFT), if we alter the stresses placed upon the tendon by changing the angle of the associated structures–in this case, the hoof–then the tendon is going to suffer.
In fact, the tendon suffers in two ways. Due to the raised heels, the tension in the tendon is also reduced and the horse will attempt to compensate as much as possible by flexing the deep digital flexor muscle–the muscle to which the DDFT is attached. But this will only work so much. The resulting slackness in the DDFT means that particularly higher impacts will cause a whiplash effect and the point most affected by this is where the DDFT runs over the navicular bone.
The second way in which the DDFT suffers is that by raising the heels, the part of the DDFT that runs over the navicular bone is insufficiently protected by the synovial bursa: it is not intended to rub in this way at this point. Juggling with the heel height will move the point of contact of the navicular bone up and down the DDFT, away from current point of irritation but to a point where new irritation will soon develop. By lowering the heels sufficiently, the protective bursa is realigned correctly with the navicular bone and pain is almost instantaneously relieved in permanence (there will still be residual irritation of the bursa where contact had been, but this will recover quickly).
Case History – Nikola
In August 2013 I was approached by the owners of a Freiburger gelding, aged 10 years, located on the outskirts of Brussels. They had owned him for the past seven years and late 2012, it was noticed that he was lame on the right forelimb. During two visits to the clinic in Gent X-ray images and an MRI scan were made. The results of these examinations indicated a thickening of the coffin bone and some wear on the navicular bone; diagnosis, ‘navicular syndrome’. The application of ‘Onion’ shoes to the front feet was advised.
As is normal in the case of navicular syndrome, this solution was not long-lasting and since the initial application, various different forms of ‘orthopædic’ shoes have been tried with the last being Denoix Reverse style with leather shims, applied two weeks before my first intervention. (It is interesting to note that navicular syndrome was diagnosed solely in the right forelimb and yet the farrier applied the same type of orthopædic shoe to both hoofs on every occasion).
One of the major reasons why the owners contacted me was because Nikola was becoming steadily more and more depressed and was quite obviously in continued discomfort despite the treatment. The prospects were becoming increasingly morbid with every passing day.
Discussion with the owners about podotrochlosis/navicular syndrome and the desperation of many professionals to place a diagnosis on something seemingly vague, I mentioned that in all probability, the problem actually lay elsewhere…at which point, one of the owners said he felt for some time that there was something wrong in one of Nikola’s shoulders.
My first encounter with Nikola showed a horse, indeed, clearly in discomfort and with feet that had been shod in a fashion all too familiar; the heels were under-run, and it was quite obvious that in the previous 10 months, no attempt had been made to correct this condition; the hoof wall was clearly deformed (see the striations in the hoof in the photo below) and the hoof walls resembled Swiss cheese, there were so many holes in them.
The first and foremost task was to remove the shoes. (Initially I had spoken of removing the rear shoes and returning 10 – 14 days later to remove the fronts but during the removal of the rears, the owners asked me to go ahead directly and remove the fronts since ‘it could not be any worse…’) This revealed, as expected, a mass of black bacterial detritus, under the leather and rubber shims, that was slowly infiltrating the white line.
Note that this first photograph is a full 90˚ profile and not taken at an angle as the image might seem to suggest.
After removing the shoes, the hoofs were given a very cursory tidy up to remove any jagged edges and some of the bacterial residue. The owners were advised to walk Nikola in the village for at least 15 minutes every day and increase the outings by 5-10 minutes every day. This encourages use of the muscles, wear of the hoofs and the blood circulation in the hoof.
I returned after two weeks to begin actual trimming. Initially just removing small amounts of hoof wall to ensure the transition was not too abrupt. Another fortnight later I reduced the walls a lot further, starting to define the correct line of the hoof wall and beginning to lose the under-run heels. This was a much more marked trim and I suggested leaving three weeks until the next intervention.
On return after three weeks, I was received as enthusiastically as before but when I posed the question about how things had gone in the previous three weeks, the owners related a tale of misery: the first four days were fine but on day 5, Nikola did not want to leave his stall…when asked what they did then, the owners told me they insisted that he walked for 10 minutes. For eleven long days! And just as suddenly as it started, it was over; Nikola strode out of his stall and took them for a long walk around the village…
And so it continued, with Nikola being walked every day and me returning initially every three weeks to keep an eye on things. He did have a couple of relapses with the appearance of abscesses–a perfectly normal occurence in a horse that has been shod for a long period of time. But each time, the owners reduced the walks in the village to 10-20 minutes and Nikola recovered from these episodes rapidly.
After three months, the owners resumed riding with steadily longer forays into the forests around southeast Brussels and Nikola has gone from strength to strength. Having been a reasonably heavy horse that would tire quickly during a long galop, he is still a reasonably heavy horse but with much greater amounts of stamina than before. Losing the shoes has not only ‘healed’ his problem of navicular syndrome but has enabled him to make full use of his hoof mechanism which augments the pumping of the heart.
Nikola is one of many horses that I have treated for navicular syndrome. All cases have shown a sufficiently large degree of success but one of the most important differences in the case of Nikola was the commitment of the owners. In too many cases, the aspirations of the owner overrule the capabilities of nature; the owner prefers an apparent cure yesterday to a real cure tomorrow. The horse must perform at all costs and taking it for ten minutes walk around the village is not preparation for next week’s gymkhana or whatever. There is naturally no question of missing the gymkhana. Other owners may not be quite so competition oriented but nevertheless, they feel themselves hampered by the fact that their horse now reacts differently when crossing difficult terrain. And so the poor horses find themselves reshod, whereafter it is only a matter of time before the pain returns…
Note about the images in this article: the two x-ray images, made at the clinic of Gent University, do not show any major problems, despite the diagnosis given on the basis of these photos. There is possibly some ossification at the rear of the coffin bone, which would not be navicular related but rather arthritic! The ‘wear’ on the navicular bone is not visible and is not likely to be, on an x-ray such as this. Furthermore, we should be talking of wear of the cartilage and not of the bone… The first profile photo of the hoof shows the condition when first encountered. The second profile photo shows the hoof 4 weeks later pre-trim; already much of the damage has disappeared after only one basic trim… The third profile photo is at three months pre-trim; there is clearly still development possible in the hoof but the under-run heels are worked out and now the principal aim is to bring the height of the heels down. The general shape of the foot is greatly improved although there is still evidence of a deformed coronary band.