© Lumient 2018

Navicular


This is the diagnosis that no one wants to hear: your horse suffers from navicular syndrome. But what does it mean and can we improve its condition?

 

First, let's look at the symptoms.

  • The horse shows lameness, usually more pronounced on one side.

  • He moves with short, choppy strides and lands on his toes, trips, is not forward.

  • Often points one foot forward when at rest.

  • Hooves typically come in two forms; either with a long toe and an underrun heel (lower than a 45-degree angle) or with excessively contracted and high heels.

 

During the veterinarian's evaluation:

  • Lameness may increase following assessments where the hooves are placed on angled blocks that force the weight either forward or backward.

  • The horse may be reactive hoof testers, especially at the back of the foot or at the frog.

  • The horse will respond well to an anesthetic block at the back of the hoof. Often lameness suddenly appears on the other, non-anesthetized hoof

  • May or may not have navicular bone damage on radiographs. Damage to connective tissue is difficult to identify unless examined by magnetic resonance imaging (MRI)

 

Ever since the development of MRI, it has become clear that navicular syndrome is more often a problem caused by damage to connective tissue (tendons and ligaments) than by bone problems. In many cases, it is possible to rehabilitate the tissues, so there is hope for the affected horses. But how does the horse damage the connective tissue in his feet in the first place, causing navicular syndrome? To answer this question, we must first define what a healthy hoof and optimal biomechanics are. This is easier said than done as even in 2018, few people have the same opinion on what exactly a healthy hoof is. There is beginning to be a consensus among some veterinarians and farriers on the elements that make up a healthy hoof. I encourage you to check the links at the bottom of this page to listen to Drs. Bowker and Taylor opinions on this issue.


Anatomy

When evaluating a hoof, we tend to focus on the external appearance of the hoof, such as the length of the toe or heel and the angle of the wall with respect to the ground. Although these are important indicators, they don't take into account the quality of the internal structures of the foot. The scientific research of Pete Ramey, Dr. Robert Bowker and Dr. Debra Taylor highlighted the importance of evaluating internal structures to truly determine the health of hooves. The level of development of these structures (or their absence) also seems to predict the chances of maintaining a healthy horse over the years, particularly with regard to navicular-type problems.

In this view of the hoof of a wild horse cut through the center, we see a beautifully developed plantar cushion just above the frog. When healthy, the cushion is made of dense fibrocartilage and has a multitude of micro blood vessels to help dissipate the forces created by the hoof's impact with the ground. The cushion and frog protect both the deep flexor tendon (DFT) and the navicular region. The lateral cartilages (not visible in this view)are on either side of P3, the bone of the third phalanx. They help to keep the hoof healthy by allowing lateral twisting (for example, if a heel on the side of the heel lands on a rock or if a horse moves in a circle). Since most terrain is uneven, it is important to allow the hoof to flex a little to adapt to it.

 

What are the optimal biomechanics?

 

Many experts now agree on the following principle: to have optimal biomechanics that will minimize tension on all tissues, horses must put their feet on the ground with their heels first. Looking at the anatomy, it seems pretty obvious why. If you were a 500 kg horse, would you prefer to land on your toe (the front of the hoof), on a bone (P3) or on tissues designed to absorb and dissipate energy, such as the frog, the plantar cushion and the lateral cartilages, all of which are well nourished by a vast network of blood vessels?


The common expression "use it or lose it" also applies perfectly to the posterior part of the hoof. If the horse does not put his heel down first, all tissues designed for energy dissipation will atrophy. During a heel-first landing, i.e. a biomechanically optimal one, here is what happens in the hoof:

  • The flexible tissues (plantar cushion, lateral cartilages, frog) widen under the pressure of the foot hitting the ground, creating expansion and torsion at the back of the hoof.

  • This expansion creates a negative pressure that draws a significant amount of blood into the tissues within the hoof capsule.

  • The bony column descends to the ground, compressing on a plantar cushion and lateral cartilages now filled with blood to dissipate energy (theory of hemo-dynamics by Dr. Robert Bowker)

  • P3 tilts slightly backward and releases the deep flexor tendon, releasing the navicular region

  • The hoof then tilts forward, the posterior part (also known as the caudal part) contracts and thus pushes the blood flow out of the hoof.

  • The pressure is transferred to the toe area (P3) and completes its cycle by pushing off the ground.

 

 

What happens when a horse has poor biomechanics?

 

If the horse has a frog infection, for example, or its hoof has never developed properly and is sensitive in the back of the foot, it will avoid pain by changing its biomechanics to land toe first, which will have the following effects:

  • It lands on the front of the hoof and therefore directly on a bone (P3) that is not designed to dissipate the forces of impact with the ground in any way.

  • The hoof must then fall back onto the heel where tissues will not be well vascularized since the expansion has not occurred. This motion creates a lot of tension on the deep flexor tendon (DFT) and navicular area.

  • The DFT will be subjected to a second tension when the foot rocks forward, irritating the fragile navicular area.

 

The conventional palliative approach in the presence of navicular

 

Current recommendations when a horse is diagnosed with navicular syndrome are typically as follows:

  • The application of an eggbar or barred shoe.

  • The addition of a rigid plastic pad and/or the application of a poured-in silicone pad.

  • Raising the heels using a degree pad, which further propels the hoof onto P3, increasing the pressure there.

  • The addition of daily anti-inflammatory drugs (such as Previcox or butazone).

 

In my opinion as well as the opinions of the people I have trained with, all these approaches are palliative and not therapeutic. Why do I say that? Because a treatment that does not directly affect the disease or that relieves it without being able to cure it is called palliative.

 

Then why can the horse appear better at first? Because these approaches will provide temporary relief by slightly shifting pressure to an area that might be less sore. As the shoe is now even more rigid, it will further limit the movement of the back of the hoof and consequently reduce blood circulation even further. The hoof will thus be more numb (therefore temporarily less painful) but will never heal or improve. The lameness will inevitably reappear because we are not addressing the source of the problem. We're just masking the symptoms.

 

A truly therapeutic approach

 

The only way to solve the problem is to ensure that the horse regains optimal biomechanics and rebuilds the tissues at the back of the hoof. The best way is to place the horse on a ground that encourages stimulation of the back of the foot without making it painful. Several rehabilitation specialists, including Dr. Robert Bowker in the USA and Nic Barker of Rockley Farm in England, have set up therapeutic centers that offer the following conditions for horses:

  • Providing 24hr/day access to footings mainly comprised of small round stones (pea gravel).

  • A turnout system consisting of a track (instead of a rectangle). This approach has been proven to significantly increase movement in horses. It's known as Paddock Paradise.

  • Life in a herd.

  • A nutrition program offering grass hay that is low in non-structural carbohydrates (see the laminitis section for more details) as well as quality vitamins and minerals.

 

All this encourages movement. Generally, biomechanics is quickly improved because soft and conformable surfaces stimulate the back of the foot while maintaining comfort. Remember that it's normal for a horse to land on his heels; it only lands toe first to avoid pain. In the absence of pain, he will voluntarily return to a heel first landing.

 

Obviously, not all of us have the luxury of having access to a Paddock Paradise....which does not make rehabilitation impossible. My tool of choice to restore optimal biomechanics is the use of boots and pads. Why? Because the pads restore comfort, which encourages the horse to land properly, and the boots protect while allowing the hoof to expand and flex (unlike a fixed metal shoe). This expansion/flexion improves blood circulation for better impact dissipation. Keeping the frog healthy and infection-free is another key factor for achieving success. For more information on the use of boots for rehabilitation, click on my boots page. My second choice is to proceed with glued composite shoes. This option has the advantage of requiring less intervention from the owner but it's more expensive and its application to the hoof is complex.

 

I encourage you to observe your own horse in motion. If you notice that your horse lands incorrectly, it would be very important to change its movement. Otherwise, it is very likely that your horse will develop navicular-type problems in the medium term.

 

Here is an example of a horse observed during a clinic that had been diagnosed with navicular syndrome. The quality of the video is far from perfect but it illustrates well how quickly you can modify the biomechanics of a horse. Please observe the following behaviours:

  • His gaits are choppy and without impulsion even if though he is returning towards the stable and therefore, his friends.

  • His body is stiff and tense.

  • He lands toe first therefore on a bone (P3) and loads the back of his hoof in a secondary way 

  • There is no suspension in his movement. His strides are short. 

Here's the same horse five minutes later. No trimming has been done. The only thing we did was to fir him with 4 boots with pads to support and protect the back of his feet.

 

Note the following:

  • His movement is more fluid and his impulsion is greater even though he is moving away from the barn and his buddies.

  • His body is much more relaxed

  • He lands on his heels and therefore loads the back of the foot.

  • He has suspension in his movement and his strides are longer.

As a trimmer, I have learned to assess the posterior part of the foot both through palpation and observation of the biomechanics of the horse when it moves. In the presence of a weak hoof and incorrect biomechanics, it is my role to find a way to restore comfort in the back of the foot in order to encourage the horse to regain optimal biomechanics, i. e. a heel first landing. Even a bad hoof can improve with time and good stimulation. If you would like more detailed information, I encourage you to consult the links below.

 

Dr. Debra Taylor of Auburn University

Is the hoof smart? Adaptability of the equine foot

 

Pete Ramey

Newly Discovered Shock Absorber in the Equine Foot

 

Digging for the truth about navicular syndrome

 

Dr. Robert Bowker

The digital cushion 

navicular syndrome

Peripheral loading

Osteoporosis of the coffin bone