Navicular Syndrome

An MRI image - Magnetic resonance imaging (MRI) allow vets to take a closer, detailed look at all the structures in the foot - bone, cartilage, tendons and ligaments.  

An MRI image - Magnetic resonance imaging (MRI) allow vets to take a closer, detailed look at all the structures in the foot - bone, cartilage, tendons and ligaments.  

Navicular syndrome is a debilitating condition responsible for over a third of chronic lameness in horses. If your horse is diagnosed with the condition it must feel like a crushing blow, but do not despair! Nowadays there’s so much you can do to manage a horse with navicular syndrome and research into this troublesome condition is progressing at a rate of knots. 

The more we understand about the underlying processes, the more able we will be to treat navicular successfully, giving afflicted horses the best quality of life possible.  Here is all the information you need to fight the battle, along with some encouraging advice from owners with first-hand knowledge of the condition.

Here our expert, vet Charlie Tomlison breaks the condition down.

What is navicular syndrome?

Navicular is not a single disease per se, but more of a “syndrome” where multiple structures may be implicated. The navicular bone is a small boat-shaped bone, sitting at the back of the foot and tucked behind the larger pedal bone.  It’s held in place by a number of ligaments. The navicular bursa is a sac filled with lubricating synovial fluid positioned at the back of the bone to cushion the deep digital flexor tendon as it passes over the navicular bone. Pain associated with navicular syndrome can come from damage to any of these structures supporting the navicular bone, as well as direct damage to the bone itself. Historically, navicular disease was attributed to interruption to the blood supply to the navicular bone, “the vascular theory”.  This has gone out of favour as a major factor in navicular syndrome but treatments geared towards restoring the blood flow do have some effect, so opinion is still divided. The navicular bone takes a lot of biomechanical strain when the horse moves.  As the deep digital flexor muscle contracts, the tendon tightens and pushes on the navicular bone.  To help prevent damage to the tendon or navicular bone, a thick layer of fibrous cartilage protects the bone, and this is may be worn down in cases of navicular syndrome.

To make some generalisations, it’s more commonly found in horses with a certain foot conformation - overlong toes and collapsed heels.  There is believed to be a genetic component as navicular syndrome is more common in certain breeds such as warmbloods, thoroughbreds and quarter horses.  It rarely affects ponies.   A susceptible conformation subjected to repetitive concussion can lead to a degenerative processs within the foot.

The average age for a horse to develop signs of navicular disease is 7-11 years, and this perhaps reflects the degenerative nature of the problem caused by wear and tear.  However, it can be seen in horses as young as 3 years old occasionally.

Symptoms

Navicular syndrome can creep up on owners unawares.  It may start as an intermittent low-level lameness that resolves quickly with a couple of days off.  In the early stages, some horses may “warm out” of the lameness, appearing stiff as they leave the stable, then improving with a bit of exercise. 

The lameness is most commonly seen in the front feet.  Usually both front feet are affected, which can sometimes make it difficult for the owner to identify.   This is because, if both feet are affected equally, there will be no obvious head-nod when the horse is trotted up in a straight line.  The stride may look short and choppy.  Lameness may be more noticeable if lunged on a circle, however, as the inside leg takes a greater strain. In some cases, the horse may stumble frequently or point one foot.

A keen eye may notice that the horse subtly puts its toe to the ground slightly before the heel lands when walked on a flat surface and viewed from the side.   This “toe-heel” action occurs because horses with navicular syndrome feel pain in their heel region.

Precise diagnosis is based on the characteristic signs, together with a lameness work-up by your vet.  Your vet may employ a number of techniques in locating the source of pain, including injecting local anaesthetic around nerves supplying the foot or into joints within the foot.  These nerve blocks can narrow down the region the pain is coming from, but recent research has shown that they must be interpreted with care as the anaesthetic can diffuse and affect areas other than those it was intended for.

If navicular syndrome is suspected, X-rays can be taken of the foot.  These focus on two things: 

The shape and balance of the foot,  i.e. how the external appearance of the hoof relates to the internal positioning of the bones within the hoof.  Here vets look at the angles of various structures in the foot to determine what biomechanical forces are applied to the hoof. 
Secondly, the appearance of the navicular bone itself is evaluated.  A number of changes seen on the bone, such as new bone formation, or loss of bone density, can indicate potential navicular syndrome.  It is worth noting, however, that some horses have x-ray changes on their navicular bones and aren’t lame, whilst others have proven navicular syndrome with no evidence of this on x-ray.

Diagnosis

Diagnostic techniques taken from human medicine have been adapted for horses.  This has taken the diagnosis of navicular syndrome to a new dimension. Magnetic resonance imaging (MRI) and Computed Tomography (CT) allow the vet to take a closer, detailed look at ALL the structures in the foot - bone, cartilage, tendons and ligaments.  This has enabled vets to diagnose soft-tissue injuries previously unseen on X-ray. 

MRI scanning is restricted to referral hospitals.  Conditions that may once have been put down to navicular disease can now be more accurately diagnosed, such as fraying of the deep digital flexor tendon within the hoof or damage to the supporting ligaments of the navicular bone. 

These ways of viewing the foot are very useful but also expensive.  Some insurance companies don’t cover their cost fully, so it’s worth bearing this in mind beforehand.

Prevention

In many cases it can be hard to see how you prevent a condition from developing when so many factors contribute to it!   However, some simple rules do apply.  Good, regular routine farriery every 4-6 weeks will help reduce the load on the heels and over the navicular bone.  

If your horse historically “feels” the ground, it is common sense to avoid riding at speed or jumping on hard ground. The repetitive concussion of riding on hard ground is inflicted on the heels and navicular region and can be enough to encourage the onset of this degenerative condition.  Avoid tight circle work unless on a soft, level surface.

Be sensible if the ground is unsuitable.  If you turn up at a competition and the going is too hard, be wise enough to put your horse back in the lorry, no matter how far you’ve driven, and curse the good weather on the way home!

Treatment

Treatment options for navicular sydrome have come a long way.  Firstly, the treatment should be geared towards the actual structures identified as involved in each individual case.   For example, a soft tissue injury may require an extended period of box rest  (over 6 months in some cases).

Corrective farriery is a vital part of, if not the main piece, in the treatment jigsaw!  Teamwork between you, your vet and your farrier can assist in keeping your horse sound and comfortable. 

The aim is to re-establish the best foot shape possible to cope with the demands of work and to fine-tune the forces placed on the foot to avoid over-loading the vulnerable areas, namely the rear third of the hoof. The feet should never be allowed to grow overlong and so make a date in your diary for shoeing every 4-6 weeks, The foot should be balanced from side to side, the toes shortened and good heel support provided.  This may take the form of a rolled toe or four point shoe, bar shoes or 10° heel wedges.  Some farriers like to use silicon pads for their anti-concussive effects.

Careful use of oral anti-inflammatories may help, such as phenylbutazone (bute).  It’s important not to make the horse so comfortable that it worsens an existing injury.

Vets often inject an anti-inflammatory, such as steroid, directly into either the coffin joint or the navicular bursa.  Injecting into the navicular bursa is the trickier but more effective option. In one study, 60% of horses were still sound after 2 months following bursa injection, compared to 34% that had their coffin joints medicated.

A newer treatment to the UK is the anti-arthritic drug, tiludronate, (Tildren™). It helps to switch off cells involved in arthritic processes.  It is given as an intravenous drip and has been quite effective in treating some forms of navicular disease where bony remodelling is a feature.  

In some cases, the vasodilator, isoxuprine has been used successfully on the basis of the restoring good blood flow to the feet, part of the vascular theory of navicular disease.

As a last resort, some owners opt for neurectomy (de-nerving operation).  This is a surgical procedure to numb the foot by cutting the nerves that supply it.  It is often used as a last resort as there are many risky consequences associated with de-nerving, such as dangerous stumbling or development of severe foot abscesses.  Sometimes the nerve grows back or forms a painful lump called a neuroma.  Many governing bodies, such as the FEI, do not allow de-nerved horses to compete.  Despite this, for some horses and owners it proves to be a valid option and they continue a happy, pain-free life for many years. 

 

More about our expert

Charlie Tomlinson (Briggs) is an equine vet working for Hale Equine Vets in Wiltshire.  She’s worked at various large equine referral centres and is a keen horse woman having owned and competed horses all her life. Her main areas of interest are equine orthopaedics and breeding. Find out more at www.haleveterinaryhospital.co.uk/equine