Navicular disease: what all horse owners need to know

• This article has been edited and approved by Karen Coumbe MRCVS, H&H’s veterinary advisor since 1991.

Navicular in horses relates to problems associated with the navicular bone in the horse’s hoof and is a common diagnosis for lameness in the front foot. The label navicular disease is used to describe a variety of conditions, including a progressive degenerative condition involving the navicular bone (which is located behind the pedal bone inside the hoof capsule), the bursa (the joint capsule that sits around the bone) and the deep digital flexor tendon (which runs over the navicular bone before attaching to the pedal bone), of one or, more commonly, both front feet.

Navicular is not a single ‘disease’ – it is a syndrome of abnormalities. Although the term – along with ‘navicular syndrome’ or ‘palmar foot pain’ as it is sometimes known – was once widely used as a generic diagnosis of heel pain, thanks to advances in technology, vets now use the term ‘navicular disease’ to specifically refer to changes within the navicular bone structure itself, identified by MRI scanning.

Navicular in horses: Signs | Diagnosis | Causes | Treatment

Signs of navicular disease

Navicular disease typically affects both front feet, although one foot is often worse than the other, so your horse may initially appear lame on one front leg. However, on the lunge the horse may show lameness on the inside leg in both directions.

You may also notice that he lands with the toe of the hoof first, ahead of the heel. In addition, navicular generally worsens with hard work and lessens with rest. None of these signs add up to a definitive diagnosis of navicular, but are possible clues. There are navicular bones in all four feet, but associated lameness almost always occurs in the forelimbs.

Diagnosing navicular syndrome in horses

If you suspect your horse may be suffering from navicular disease, you should contact your vet. They are likely to review the whole clinical picture, assessing the feet and shoeing, together with the way in which the horse moves, a well as performing flexion tests and nerve blocks to assess the affected area to see if this reduces the lameness.

Historically the term navicular syndrome came into use 15 or so years ago to describe lameness confirmed as being within the foot and heel region. Diagnosis was reached using nerve and joint blocks and where irregular margins (edges) to the navicular bone were evident on radiographs (X-rays).

The use of MRI has enabled accurate diagnosis of damage to soft tissue structures, such as injuries to the deep digital flexor tendon, the impar ligament and collateral ligaments of the distal interphalangeal (coffin) joint. Vets can also see increased fluid in the navicular bursa and distal interphalangeal joint via MRI, which may indicate inflammation of these structures.

Furthermore, MRI can also detect changes in bone. As it creates images as ‘slices’ through the foot, rather than two-dimensional images where anatomical structures are imposed upon one another, it offers greater potential than radiographs alone to highlight mild or early navicular bone changes.

Now that vets can pinpoint issues in the navicular region by using MRI, they no longer have to lump everything under one umbrella term.

This ability to diagnose specific injuries within the foot much more accurately is one of the main reasons for the apparent decline in the number of horses diagnosed with navicular disease.

That said, many vets have now come full circle and are once again willing to diagnose navicular disease, particularly in those horses where MRI indicates predominantly bony changes with minimal soft tissue involvement.

Causes of navicular problems

The causes of navicular disease are many and varied, and are not solely down to the influence of genetics.

We know that bone adapts to stresses placed upon it; it is thought that excessive stresses may lead to inappropriate adaptation and degeneration of the navicular bone.

Skilled farriery can lessen these harmful stresses, which is perhaps another reason why fewer horses today suffer from foot pain.

Poor conformation or the development of a long toe and a low heel will only add to the stresses placed on the navicular region during exercise, so it is important that these shortcomings are addressed with appropriate farriery. Even the well put-together horse can suffer, however, if hooves are not kept properly trimmed and balanced.

Possible contributing factors include:

• Although it’s found in all breeds of horses, it’s most typically diagnosed in quarter horses, thoroughbreds and warmbloods
• Underrun heels, sheared heels, contracted heels, mismatched hoof angles, and disproportionally small feet may all be contributing factors in a predisposition towards navicular
• Affected horses are usually between the ages of 7 and 14.

Treatment for navicular in horses

The treatment for navicular is as varied as the possible causes so you will need to take veterinary advice regarding the various options appropriate for your horse.

If it is thought that foot conformation may be a factor, therapeutic shoeing may help a lot, especially in the early stages. There are many different approaches. One school of thought is that it is best to remove shoes to improve the blood flow to the feet, but others choose corrective shoeing, using a shoe that supports the heel and can reduce the load exerted on the navicular bone by the deep digital flexor tendon. Your vet and farrier can advise you on the best course of action for your horse.

Rest and controlled exercise can be useful, especially in the early stages, when it can help to reduce the stresses on the navicular bone, particularly in conjunction with an appropriate change in shoeing.

Many horses respond well to a combination of medication and effective farriery.

There are several different medical treatments available including painkillers that also have anti-inflammatory effects, to the newer bisphosphonates, which regulate bone metabolism. Some studies have suggested these bisphosphonates are useful, however it is unclear at what stage they work best.

Case series of navicular disease have shown a favourable prognosis, at least in the short term, with medication of the navicular bursa (the area around the bone itself) using corticosteroids and/or hyaluronic acid.

As navicular worsens with hard exercise, you may also need to look at reducing your horse’s workload. While riding avoid hard, concussive surfaces, surfaces with a camber and tight circles. This will reduce the concussion and uneven forces on the foot.

Surgery is sometimes considered as a last resort; there are different options reported, with the traditional surgical treatment, known as ‘nerving’ or ‘denerving’ being more common, when other treatment options have failed. This involves cutting the palmar digital nerves, so the horse loses sensation in the heel. As with any surgery, this is not without risk and may only mask the issue, causing more serious problems in the long term. There is a chance of the nerves re-growing and on average the procedure offers a mean of 20 months of successful performance. It will only work in cases where a nerve block to those specific palmar digital nerves has been positive.

While we still do not know exactly what causes degeneration of the navicular bone and its associated tendons and ligaments, in terms of imaging and awareness, at least, we have moved on in leaps and bounds in the last 15-20 years with the advent of MRI and improvements in equine foot care.

References

• https://www.ncbi.nlm.nih.gov/pubmed/25724857 – Is there an association between clinical features, response to diagnostic analgesia and radiological findings in horses with a magnetic resonance imaging diagnosis of navicular disease or other injuries of the podotrochlear apparatus? – Jan 2015