Navicular Related Lameness

Navicular Syndrome/Disease

It is speculated that Navicular Syndrome is responsible for about 1/3 of all chronic forelimb lameness in horses.  Although the Navicular region of the hind limbs can be affected in the same way, most Navicular Syndrome diagnosis are on the front feet.  The terms Navicular “Syndrome” (NS) and Navicular “Disease” (ND) are often used synonymously; however there is a definite difference.  There are generally less than 10% of all horses diagnosed with “Navicular Syndrome/Disease” that actually have radiographic changes or significant degeneration of the Navicular bone (NB).  Over time there has been considerable debate regarding a Navicular diagnosis. It seems that typically horses could exhibit all the clinical signs of Navicular disease, but have no radiographic changes to the bone.  Typically if a horse had heel pain, pain through the frog, and diagnostic anesthesia that localized the area around the Navicular bone, it would receive the diagnosis of “Navicular Syndrome” because the pain seems to be in the Navicular region.  The use of the term “disease” seems to be reserved for cases where actual changes to the Navicular bone are seen, however even then it is a guarded prognosis because calling it a disease would imply that the cause is known and a specific treatment can be implemented.  Until recently, the NS diagnosis was vague in many cases.  Because both the cause and structure being affected was not fully known, the prognosis for most of these cases was less than bright.  Most horse care professionals and horse owners grew to accept that the NS diagnosis meant limited use of the horse with regular administration of anti-inflammatory injections or a neurectomy.  It was also commonly accepted that the horse would have frequent bouts of discomfort for the remainder of their life.  However, over the last 15 years or so, there have been marked improvements in understanding the lameness in the Navicular region.  With the advent of standing MRI for horses and high quality ultrasound, veterinarians are able to see pathology to connective tissue around the Navicular bone and the distal interphalangeal (DIP) joint, long before changes to the bone are seen radiographically.  Lesions to the collateral ligaments of the DIP joint and the collateral sesamoidean ligament (suspensory ligament to the NB) seem to represent a large portion of the current findings with MRI and ultrasound.  If left untreated, the lesions can become chronic and progress to arthritic lesions.  Typically, cases would reach the radiographically recognized state before a definitive diagnosis could be made.  Today, more specific and comprehensive equipment are available to diagnose the condition so treatment can be more effective.

 

List of Specific Diagnosis within the “Navicular Syndrome” Group

    - Bone Spurs of the Navicluar Bone (NB)

    - Increased Vascular Channels in the NB (often referred to as “Lollipops”)

    - Arthritic Lesions of the:

        • Deep Digital Flexor Tendon (and/or tendon sheath and bursa)

        • Impar Ligament

        • Collateral Ligament of the DIP Joint

        • Collateral Sesamoidean Ligament

    - Navicular Bursitis

    - Coffin Joint Disease or (Sub-condral bone bruising)

    - Caudal Hoof or Heel Pain

 

Probable Causes of Navicular Region Lameness

For years the cause of “Navicular Syndrome” has been speculated and debated.  In general the debates and speculations have centered around heridity and hoof balance.  Some feel that NS is hereditary and that certain breeds and blood lines are predisposed to having Navicular region lameness.  Another school of thought is that NS is caused from excessive leverage from a long toe and other hoof imbalances.  Within the last 5 years, the later seems to be the more widely accepted theory in light of the soft tissue lesions occuring before bone changes are seen.  The “hereditary” theory does have some valid points in that many horses have a hoof and limb conformation that makes hoof balance challenging.  There are some breeds that were seen as being “pre-disposed” to Navicular Syndrome because of their conformations.  For example, Quarter horses because they often had big bodies and little feet, and Thoroughbreds because they had flat feet with said to be poor heels and therefore prone to a broken back pastern axis.  Although those specific breeds do tend to have those conformation generalities, the real problem lies with the hoof care trends associated with their breed/discipline.  

Over the last 30 or 40 years, the quarter horse industry has been promoting a foot with taller heels as a desired model.  If you are able to check out the "Natural Balance Hoof Care" book and videos, you will see clearly that taller heels and resulting lack of frog contact means insufficient support to the Navicular bone and the soft tissue surrounding it.  Ultimately, the soft tissue fails and pain and trauma in the Navicular region is seen.

In the Thoroughbred industry, the trend used to be towards achieving a longer toe to increase the length of stride.  Although the frog would end up closer to the ground, the heels were often underrun and crushed.  The extra leverage from the long toe again leads to strain on the soft tissue in and around the NB and the DIP Joint.  A toe-first landing also tends to go hand-in-hand with the long-toe/low-heel hoof shape.  In short, the impar ligament, collateral sesamoidean ligament and the DDFT received additional strain and trauma at both the landing and breakover phase of the stride.  The eventual result of the extra leverage would appear as a “Navicular” lameness.  

From the hereditary stand point, breeds like Quarter horses and Thoroughbreds appear to make the theory plausible.  However I do not believe that there has been enough consideration regarding the hoof care practices specific to certain breeds or disciplines.  I think as more and more veterinarians and farriers have started to look at some of these hoof care practices with some discretion, it is becoming more evident that Navicular region lameness is indeed a result of unnatural biomechanical forces from such things as: hoof imbalances, excessive leverages, horses working on hard or unforgiving surfaces, and horses standing in confinement more than they are allowed to be active.

 

General Treatment Approach for Navicular Region Lameness

For the last 20 years or so, the standard treatment prescription for “Navicular Syndrome” has been egg bar or straight bar shoes and often wedge pads.  The bar shoe was used to offer additional support to the heels or caudal part of the foot, while the wedge pad was perceived to improve the angle or pastern alignment.  In general, the treatment was met with some success.  The success or failure seemed to depend on foot preparation, specifically of the heels.  If the heel was trimmed to a solid base and the shoe’s extension behind the heel was conservative so it did not cause undue pressure on the heel, and the bar was positioned so that the back of the frog could be in contact, then the treatment was fairly successful.  The bar catching the frog as it descends is helpful to offer some support to the Navicular region.  At the same time, it was acceptable to roll or square the toe on bar shoes to reduce the leverage at the time of breakover.  The use of a full wedge pad, in conjunction with a rolled or squared toe bar shoe, helped with the alignment of the pastern plus added more support to the frog.  

This approach has helped thousands of horses find some relief from the Navicular region pain.  Typically horses would improve by 60% to 70% and would hover around that level of soundness for a few years.  Over time, many horses would start to do poorly after several years and the next line of treatment would be a neurectomy (Nerving), which would basically remove the pain in that region, but not really fix the problem.  If the “cause” of the pain was not addressed at the time of the nerving, it was not uncommon to see the same lameness level or worse return within a two year period.  

Over the last 10 – 15 years, improved treatment approaches have surfaced for these cases. Simply getting the hoof wall balanced around the widest part of the foot, and trimming the wall level or parallel with the live sole, seems to help set the stage for a healing environment.  From there, even better results are seen by reducing the leverages around the coffin joint with a more rounded edge shoe as well as incorporating some well distributed caudal foot support.

 

Example of Toe-First Landing                                                   Example of Heel-First Landing

 

Figure 1

 

 

 

Figure 2

 

    For cases where the condition is chronic and there are radiographic changes to the NB, the best approach has been the EDSS treatment system because of its adjustment capabilities.  There is no real need to offer additional clearance for a prolapsed sole in the toe (as there is in laminitis), so we typically fill the whole bottom of the foot with impression material.  Once the EDSS shoe and pad are applied over the impression material, it is easy to make adjustments with the rails and frog inserts to help the horse turn comfortably and engage the ground slightly heel first.  

The way the horse engages the ground (ie; toe-first, flat or heel-first) is what really determines what type of application the horse may require.  For example, if after the foot is trimmed the horse lands heavy toe-first, then you would apply something like the EDSS so that you can make the necessary elevation adjustments.  If the horse lands slightly toe-first or flat, then you might get the required elevation with a standard (NB, CF or PLR) shoe and wedged frog support pad.  If the horse can land heel-first after trimming, then you may get by with  a NB shoe or even barefoot.  However, typically with these cases the caudal part of the foot has enough distortion and atrophy where a flat frog support pad may be very helpful.  The package that is most widely used on “Navicular” horses is the Aluminum Natural Balance shoes or Aluminum NB PLR (performance leverage reduction) shoes, wedged Natural Balance Frog Support Pads, and Sole Support Impression Material. (Figure 1)  If the use of pads is required for more than a few shoeing cycles, then many people find it helpful to alternate the use of Impression Material with something like Magic Cushion after about the 3rd shoeing.  Keep in mind that support to the back of the foot and the reduction of leverage is your goal, so choose your package carefully and make sure you get the appropriate instruction for the products you are using.  Along with proper hoof preparation, the reason the EDSS and the NB shoes and pads seem more effective than egg bars and wedge pads is because the support that is offered to the back of the foot is “Active” and not “Passive”.  What is meant by that is, the system is doing more than just catching the frog and stopping it from dropping between the heels of the shoe.  With a ‘firm’ frog support pad, there is active support to the frog (and therefore the Navicular bone and coffin joint) with each step. (Figure 2)  By using an aluminum rolled toe shoe, or better yet a complete leverage reduction shoe, you are taking the extra strain off the collateral ligaments, collateral sesamoidean ligaments, impar ligaments and DDFT.  Aluminum is even more effective because the horse will easily wear the balance point of breakover to its most optimal location.

The preferred approach of 15 – 20 years ago was useful in getting the “Navicular Syndrome” epidemic a treatment direction.  The tools and techniques we have today are just another step, but do seem to offer a little more hope for lame horses.  As more information about the specifics of Navicular Region Lameness is discovered, I’m sure the products and techniques used to treat the syndrome will continue to improve.


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