Navicular syndrome is a very common problem in the equine industry, likely impacting 30% or more of horses, dependent on the breed and discipline. We see this condition commonly in the western disciplines but also to varying degrees in other sports, including jumping, dressage and even racing. There are many factors that contribute to the problem, which can make it difficult at times to manage.  All too often, though, we tend to wait until the condition has progressed, with irreversible damage, before we properly intervene.  With a better understanding, hopefully we can recognize the condition sooner, see contributing factors and produce better results for the patient in the long term.

When we mention the words “navicular disease“, we really have to define what we are referring to in the patient.  The condition is quite complex, having various stages of development, some more readily recognized than others.  Given this, we often use the term ‘navicular syndrome‘ as this can be more accurate, encompassing the many stages of progression.  In some horses, we use the term ‘caudal heel pain‘, which is not far removed from ‘navicular syndrome’, as it is likely just a general categorization for the patient.

Overall, the situation in which we have heel pain and lameness is quite common in equine practice, involving many structures within the caudle hoof including the navicular bone, associated ligaments, joint capsule, navicular bursa, deep flexor tendon and even collateral cartilages of the coffin bone. Due to progression or stage of the condition, localization of the exact source of pain can be difficult as many other areas are impacted due to compensation. This is often seen more in chronic cases, evident not only by heel pain, but also stiffness higher up in the limb, including the shoulder and even neck region.  In some cases, we will see toe sensitivity, due to improper loading and landing of the foot.  In others, especially with progression, we may see compensatory lameness even in a rear limb or lower back.

Clinical Signs

In most of these patients, we can appreciate a reluctance to move forward, with a reduced forward or anterior stride.  The reason for this is that if a horse fully reaches out, they are forced to land heel first, putting more pressure on the heels upon landing.  If the heels are sore, they are reluctant to move out, thus a protective gait comes into play, resulting in a shortened anterior stride, landing more flat or even toe first with less pressure on the heels.  This is more obvious when going downhill and to lesser extents going up hills, due to foot landing. This shortened stride can become habit over time, and hard to resolve.  Many of these horses are also choppy in their gait upon circling or turning on a line.  As the problem progresses, we may appreciate more overall stiffness, especially in the front limbs, with almost a reluctance to flex or extend joints such as the knee (carpus) or shoulder region.  Some may even be reluctant to bend at the neck, due to compensation over time.

Diagnosis

This is where the tricky part can come into play.  The suspicion can be raised that heel pain exists in a patient, often by just watching their gait and overall movement.  We have many options to help localize the source of the pain, with a hands on approach being first and foremost.  The foot is involved in about 80% of all lameness cases, if not more, so in any lameness case, we need to start with the foot.  Heel pain can be appreciated simply by what we call is the board or 2×4 test.  This is when we take a 2×4 piece of wood, place it under the foot, extending out front with the heel hanging just at the back edge of the board.  Then, we simply lift the front end of the board, off of the ground, which forces the coffin joint to extend, tightening the deep flexor tendon and placing more pressure on the heel and navicular bone.  In most, lifting the board 1-2 inches off the ground is sufficient to elicit a response, which is usually with them lifting their foot off of the board due to discomfort.  A very simple but effective means of getting a ‘feel’ for heel pain.

Aside from the ‘board’ test, which is not necessarily very specific to the heel, we will examine the foot with hoof testers, determining a positive response not just in the heels, but also evaluating other points of the foot which may be secondarily painful.  In most of these patients, there is a definitive response to the hoof testers when placed across the heels.  Many also have secondary pain in the toe region, due to altered gait and landing.  At this point, if we have doubts or want to drive the diagnosis home, we will perform nerve blocks including the palmar digital nerve block, which helps to desensitize the heel region. A positive response to the PDN block can improve our suspicions of heel pain, but doesn’t completely rule out other possibilities as the anesthetic solution can drift under the skin.  Some veterinarians will go a step further and block out the coffin joint or even navicular bursa to help confirm the diagnosis.  

At this point, we have often confirmed our suspicions of generalized heel pain in the patient, but now we want to further localize and assess damage if possible.  The next step is radiographs or x-rays, getting various views of the lower foot and navicular bone.  What we are looking for is evidence of bone deterioration or even joint involvement, such as arthritis.  In some chronic and markedly progressed cases, we may even appreciate some calcium deposits in the deep flexor tendon.  We have to keep in mind that these ‘bony’ changes may not be present in every case and if present, will likely vary based on severity of those lesions.  The more early stage heel pain cases often have few bone changes present, while the more progressed or chronic cases often have more changes.  It is also worthwhile to note that in my opinion, although bony changes are significant, they are not always reflective of prognosis or severity of the lameness in the patient.

This is usually where I end my evaluation of the heel pain patient, but others go a step further.  It is not uncommon in today’s veterinary industry to have an MRI examination performed to evaluate soft tissue structures such as ligaments and tendons, in addition to gaining a better feel for bone damage.  The MRI examination can be a costly undertaking and have some risk if general anesthesia is utilized. It is often utilized in cases that are hard to pinpoint, when x-rays do not reveal the entire picture and when we are hoping to gain a better feel for overall prognosis in that patient.  As we advance in technology, we sometimes have to question value.  I think the images produced are quite spectacular and we can definitively see ‘abnormal’ versus ‘normal’ tissue and pathology, however, sometimes I think we might be jumping the gun and getting ahead of ourselves when making a prediction about that patient.

Causes and Contributors

Navicular syndrome has often been referred to as a ‘man-made condition’, which infers obviously that we, as man, have created it.  We create many of these cases over time by placing too much pressure on the heel through trimming and/or shoeing practices and creating improper load and travel.  In most, if not all of the cases, we have hoof capsule pathology in regards to imbalance.  An under-run or too low of a heel is very common, along with a toe that is too long.  This type of scenario sets us up often for excessive heel pressure and pull on the deep flexor tendon, which then compresses the heel and navicular bone structures.  On the converse side, we can also have a situation in which the heels are contracted, pulled tight, which provides little heel expansion, and sometimes coincides with sheared heels or medial/lateral imbalance.

Several cases are created due to improper foot capsule size in relation to the body of that patient, essentially trimming a foot too small.  This is often apparent in the Western Pleasure world whern many of the horses have feet that are moderately undersized for their body frame.  We can also create or induce heel pain with improper shoeing, by not having the heels adequately supported by the shoe, often hanging over upon loading.  Obviously, an overweight body condition in that patient can also contribute to the problem, which raises points about diet and nutrition.

Essentially, the main contributors to caudle heel pain and navicular syndrome involve the foot and how that foot is managed. This not only creates and sets the stage for the condition, but also strongly contributes to ongoing problems.

Management Options

To ‘treat’ a navicular case implies that we are seeking a cure for that patient. This is simply not true, nor possible, as is with most chronic health conditions. What we are seeking to do is “manage” that condition better, which then if we are successful, improves soundness, performance and overal quality of life for that patient.  In most cases, especially if there are bony changes, we will not reverse that damage, but it is possible with the right approach to slow progression.

In order to understand management options, we have to understand what we are trying to do or counteract in the condition.  It is like building a structure that will bear tremendous amount of weight.  In order to do this, we need to understand what forces we must overcome in order to create longevity and strength.

Navicular syndrome is a condition heavily influenced by the process of inflammation, which includes oxidative cellular damage. The process of inflammation is created whenever a tissue is under stress, which is the case in most of the situations by poorly balanced feet.  This long term stress creates a cellular response, inflammation, which initially starts in the soft tissue structures surrounding the heel region, from ligaments to the deep flexor tendon and even the bursa and joint capsule.  The process starts there, with ongoing tissue damage due to stress.  Inflammation continues, chronically, altering other cellular functions and even blood circulation to the region.  The heel region becomes compromised, tissues degenerate and pain is evident.  It becomes a vicious circle of events, as the process of inflammation contributes to itself, especially when combined with continual foot imbalance. Over time, bone tissue becomes involved, which then leads to variable degrees of navicular bone and even coffin joint changes, which are evident on x-ray.  

The problem that exists here is that the syndrome begins on a soft tissue level, in the supporting structures.  We may have a lame horse that presents as a heel pain patient, but the x-rays demonstrate minimal if any bone changes.  Then we often make the incorrect assumption that this is not a ‘navicular syndrome’ patient, despite clinical signs and blocking out.  We may even treat it as such, but for some reason fail to label it appropriately due to no radiographic changes evident.  These are often the horses that are then sent for MRI examinations, which then demonstrate variable degrees of changes in the soft tissue structures.  Then, some will label it as navicular syndrome, while others just present what is present in regards to the structures affected. In other cases, the horse is painful in the heel but no radiographic changes are present, so instead of managing it appropriately, some may dismiss it as a sole bruise or otherwise. Pain in the heel tells us this tissue is under stress, period. In reality, what we have is different stages of progression, but really the same bottom line problem.  

One of the most common approaches utilized includes the application of shoes with wedge pads, intending to lift the heels and reduce pressure exerted on the navicular bone by the deep flexor tendon.  This is usually done along with oral use of NSAIDs, such as phenylbutazone to help relieve pain.  In the not so distant past, it would not be uncommon to utilize other medications such as Isoxsuprine or Pentoxifylline, with intentions of improving blood flow to the lower foot.  These medications have produced variable results over the years and are not commonly utilized currently.

Other therapies utilized include injections of steroids into the coffin joint, navicular bursa or surrounding tissue, with the main intent of reducing the inflammatory response.  These steroid injections can be helpful to the patient, often producing rapid improvement in clinical signs, but they do not benefit all patients and there is even question as to whether if we are truly modifying the disease or simply reducing pain.  There is even some evidence that their use not only does not slow progression of the condition, but may actually speed things up as it is not uncommon to have horses initially respond to injections however, over time they require higher doses or fail to respond period.  

Bisphosphonates are a class of medications that are gaining popularity, initially developed to combat osteoporosis in post menopausal women.  In any case of bone deterioration, such as navicular bone or generalized arthritis, the inflammatory signaling process influences bone health.  When it comes to bone health, we have two main types of bone cells; osteoblasts and osteoclasts.  The bone is a living structure, constantly remodeling over time. Bone is being lost and new bone is being formed.  The osteoblasts are involved with new bone growth, while the osteoclasts are involved in bone degeneration.  The class of bisphosphonates, which include two main medications in the equine field, have the main intention of altering this bone remodeling through inhibiting or blocking the osteoclast function.  There has been much debate, especially in the human field when it comes to these medications, indicating that there is an increased incidence of bone pain and even fractures, not to mention other potential complications.  This is due to the altering of the normal bone remodeling pathways that are needed for health.  Equine research has indicated that use of these bisphosphonates does reduce markers of bone degeneration, but the degree to which they demonstrate this is not completely convinceable, meaning that the level to which they impact bone markers is often not significant enough to produce benefits.  Their use has not demonstrated any notable improvement in overall bone health, on follow up radiograph evaluation, which means that the navicular degeneration remains unchanged.  Despite this, many patients do benefit, at least in the short term.  What has become evident in research, is that the bisphosphonates are actually creating a state of analgesia, which means they are reducing pain in the patient.  However, it is not clear exactly how this is being done.  So, it is possible that clinical benefits are being gained strictly as a result of pain reduction, more so than bone remodeling influences. We do not know the long term effects to the patient with these medications.

Final modes of therapy, including neurectomy, are often seen as salvage type of procedures.  In these procedures, the palmar digital nerve is cut surgically, which hopefully reduces any sensation in the heel region, which means pain reduction and improved comfort.  However, there are many downside as well, including neuroma formation (nerve scar tissue), which can actually be more painful than the original condition.  Also, given the loss of sensitivity to the heel region, these patients are also subject to further foot injury due to lack of feeling anything.  We have to keep in mind, with this procedure, that we are just reducing pain, if all goes well.  We are not impacting the progression of the condition as a whole  Many competitive horses have had this procedure done as a last resort type of scenario, which opens the doors not only for ethics but also for potential injury to the patient and rider.

Pursuing Other Options

All of the management options outline above are commonly used and they can provide benefits to a high percentage of patients, but the question is for how long?  Inevitably, we may produce improvement in the patient with any of those means, but all too often, that patient continues to progress, deteriorate and exhibit more problems down the road, requiring a total re-evaluation and often higher doses of medications used. Essentially, in most, we are doing little more than numbing pain.

If we see the condition for what it is, unregulated inflammation, then we can see potentially other options to help manage it better either alone or in conjuction with therapies described above.

One of the biggest problems that I see revolves around foot care, as this is usually the culprit that lights the fire of progression.  I have seen obvious cases in which the heels are under run, with too long of toes that are not addressed, but instead ‘treated’ with navicular injections or medications.  In others, I have seen shoes applied, with wedge pads, but still that patient is lame, often not even improved post shoeing.  I have seen heels that are too far foward, clentched tight, that instead of being trimmed and balanced properly, have a wedge shoe applied.  The foot is the problem area, it is the source of our problems and if it is not addressed properly, we will continue to have problems no matter what we do for that patient. Personally, I choose a barefoot trim in all of our heel pain patients as I have not gained any benefits from shoes over my career. I feel through the barefoot approach, we can allow that foot to grow and do what it ‘wants’ to do to restore comfort for that patient.  We can allow the heels to grow properly, relax and expand, without the restrictions of metal being applied.  This process can and does take time, but in most cases, moderate improvement is gained in just the first couple of trims, especially when combined with the proper therapy approach. In reality, with shoes we are trying to make ammends for shortcomings in the foot, such as low heel.  So, if that is the case, why not simply just allow the foot to grow, rather than artificially modify it?

Stretching is one of the most important parts of a therapy program, helping to reduce secondary lameness and/or tightness that has developed. Many of these horse flat out refuse lateral neck bends or forward stretching of the legs due to muscular contraction over time.  As we work with these patients daily, the stretching becomes less of a battle and the patients actually begin to release.  We can work our way down the leg, in regards to lameness, as we cannot forget that in many there is compensatory neck and higher leg pain.

Inflammation is the bottom line problem we are looking to manage, but all of the above in regards to foot care and stretching contribute to this process. We will not be successful in management of the inflammatory process in that patient if we do not reduce or better manage the contributors, such as hoof balance.  Inflammation is induced by tissue stress, so we must reduce that stress, on a physical and emotional level.  Every lame horse in pain, is likely also under emotional stress, which can further contribute to the problem.

I chose to manage the inflammatory process through the use of herbs and nutrition.  We have to remember that the inflammatory response is not just in the heel region, but in most has now involved the entire body.  An injection will only assist us partially with that local inflammatory response, but dooes nothing for the body as a whole. Through the use of herbs, we are actually restoring or rebalancing the inflammatory process, not completely turning it off as is seen with many medications.  We don’t want to turn it off, as inflammation is a necessary part of health and when we do that, problems develop to the other degree.  Herbs including Curcumin, Boswellia, Algaes, Ashwaghanda and even Flax can help us to balance that inflammatory response and even combat oxidative damage.  We use them in combination, often in high doses, to work together for better long term results.  When we combine the right herbal approach with proper trimming and stretching, the patients often respond dramatically.  However, our long term gains are going to be limited by the extent of damage occurring over time.  This is one reason why we need to act proactively, ideally in the early stages or even on a preventative basis in those horses that are more predisposed.

In our equine patients with heel pain, our treatment approach first starts with the foot, correcting balance, reducing breakover and adjusting the heel as needed.  In many, that heel length or height needs to be reduced, or pulled back, while in others, it is fine, but more so toe length needs adjusting.  In terms of approach to supplements, we will manage each patient somewhat differently, dependent on their level of discomfort.  In those patients with high degrees of discomfort, I will often start with our Cur-OST EQ Pure or EQ Plus formula, to address inflammation but also oxidative damage..  In those patients with less discomfort, especially if they are easy keeper types, we will employ the benefits of the Cur-OST EQ Total Support, with the goal of balancing inflammation but also addressing underlying gastrointestinal problems which may be the root problem.  Other additional supplements that we will use work together with the above mentioned approaches, but include adding in the Cur-OST EQ Nourish and even the Cur-OST EQ Nitric Boost.  

Other modalities include herbs and other food sources that may help us not only rebalance inflammation, but also by positively impacting circulation to the foot and other areas of the body.  Nitric oxide is a gas produced in the body that is often inhibited in high levels of inflammation.  Nitric oxide is needed for vascular health, helping to dilate blood vessels and improve blood flow.  L-Arginine is one amino acid that is involved and has shown benefit in regards to improving nitric oxide levels and vasodilation. There are many others, a few of which we are exploring in our research, which not only balance inflammation but also improve nitric oxide production in the body.  One area of interest is use of food groups that are rich in nitrates, which can be a direct source for nitric oxide production in the body.  Our preliminary clinical data is encouraging in this field. Both the Cur-OST EQ Nourish and Cur-OST EQ Nitric Boost can benefit the patient in regards to nitric oxide production.  I do think, based on experience, that the added protein in the EQ Nourish can be especially beneficial in some of these patients, somehow impacting inflammation and even bone health positively.

Through better management of the inflammatory process, we can not only improve pain levels, but potentially slow the overall degenerative process. Bone remodeling is a definite concern, as is evident with bone loss in navicular cases and even lower hock arthritis.  This is where the bisphosphonates have come into favor, but again, the data is not quite there to truly determine how they are working.  What is noteworthy is that through the use of various chelated calcium metabolites, we may be able to actually impact the bone remodeling process, restoring it to a more balanced state.  This has been noted in various research articles on bone loss in post menopausal women.  This too, is an area of investigation in our research laboratory.

The Bottom Line

The bottom line here is that there are many options of therapy and better management for these patients.  With earlier intervention and detection, not necessarily implying the need for an MRI, we can hopefully catch the process at an earlier stage which then gives us better odds of successful management. We should not just accept the ‘need’ for an injection of even a specialized metal shoe.  We need to understand the process at hand and through this understanding, we can actually see better options and utilize them appropriately.  We have made huge strides in many patients, in our rehab program, but this is through seeing the entire picture and addressing every contributor if possible from diet to trimming and supplement use. 

The best success cases come with early intervention.  Even better results are evident when we take a preventative approach for those patients at higher risk.

At Nouvelle Research, Inc., we are here to help!  

 

Tom Schell, D.V.M.

Nouvelle Research, Inc

www.nouvelleresearch.com

[email protected]

 

 

 

 

 

 

 

 

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