pair of shod horse's hooves - the news on navicularLike laminitis, navicular is one of the most common and dreaded hoof conditions out there. Also like laminitis, its causes are still not fully understood, its presentation can be very different horse to horse, and its treatments are wide-ranging. Just as there’s no single cause, there’s no single way to manage it, either. But armed with information, navicular syndrome can be dealt with more effectively.

What We Do Know

Navicular syndrome doesn’t refer to a single disease. Rather, it’s the term generally applied to a number of conditions affecting the navicular bone. It’s also called “caudal heel pain syndrome,” often by vets, to indicate that there’s range of problems that could be leading to lameness in that area.

The bone itself (also called the distal sesamoid bone) is a small, flat bone located at the back of the coffin joint. The impar ligament joins it to the pedal bone, and the suspensory ligaments attach it to the pastern.The deep digital flexor tendon passes over it and is cushioned from the bone’s surface by a sac of fluid called the navicular bursa. Basically its function is just that – to provide a smooth surface for the tendon to pass over as it changes angles before attaching to the coffin bone.

Some breeds seem to be more predisposed to developing navicular problems, leading to a suspicion that there’s a genetic factor at play. Thoroughbreds, Quarter Horses and Warmbloods seems to be more at risk.

Other risk factors include conformation, particularly small or malformed feet, contracted heels and underrun heels. Age seems to play a role, as well – it’s typical for horses to develop signs of navicular problems between 7 and 14.

What Might Cause Navicular Issues?

With such a large number of important soft tissue structures attached or in close proximity, trauma to those tissues can result in damage to the navicular bone itself. Inflammation, injury and damage to any tendon or ligament can result in pain in the navicular area.

Damage to the bone itself is another primary cause of navicular issues. That damage could be the result of injury or trauma, such as a fracture, or the result of chronic disease or degeneration of the bone’s surface, such as lesions.

Changes to the blood supply to the region is thought to be a factor, but what might cause that interference, and the mechanics of that condition, aren’t fully understood yet.

What are the Signs?

Horses with navicular issues show a range of reactions. They can exhibit low or high grade lameness, show lameness in one or both front feet (although it’s typically a bilateral condition, one foot might be more painful) and be consistently or intermittently lame. They might only appear lame on hard surfaces, or on tight circles. It’s typical for the affected (or more affected) foot to show a greater degree of lameness when it’s on the inside of the circle. Lameness associated with navicular syndrome is usually recurrent. It will get worse with work, and better with rest, which makes sense.

Their gait can alter as they try to avoid putting weight on their heels, so it might appear that they’re putting their toes down first. In serious cases, horses might point the more painful toe forward or keep that leg in front of themselves.

How is it Diagnosed?

You can expect that a veterinarian will start with some hoof testers and want to do a nerve block of the foot to locate the source of the pain. It’s not uncommon in cases of bilateral issues to have the horse become suddenly lame on the opposite leg once the more painful foot has been blocked.

Flexion tests might be recommended as a part of the exam. It’s also standard to do some imaging to detect any damage to the bone or to the surrounding structures. Radiographs can be a bit misleading in this situation, however – some navicular bones seem to show damage and are actually completely normal for the horse, while some horses with navicular-related pain show no changes to the bone structure at all.

How is it Managed?

There are a range of treatments available, from the conservative to the cutting edge. At the most basic end there’s anti-inflammatory pain medication and corrective shoeing, which seem effective in many cases. Plenty of horses can continue their careers with just these measures in place, but it’s key for owners to develop a plan with both the vet and the farrier.

Farriers will typically create shoes that support the horse’s heel as much as possible and provide an easy breakover. Rolled toe or rockered shoes are often used, or the shoe might be set back from the toe a bit to encourage breakover. In terms of heel support, egg bar or heart bar shoes are common. Farriers might also recommend a small wedge pad at the back to relieve pressure.

If foot conformation is part of the problem, imbalances and asymmetries in the hoof will need to be addressed slowly so the horse can be brought back to balance. Owners should expect to see their hardworking farriers every 4 weeks at first.

Depending on the severity, the horse’s intended use and the owner’s budget, more hard-core treatments are also available. Injecting the navicular bursa with a corticosteroid, or hyaluronic acid might be advised to provide the flexor tendon with a more cushioned surface to run over. Injecting the coffin joint is also an option to decrease inflammation. If the issue is related to decreased blood flow, a vasodilator like isoxsuprine could be prescribed.

Bisphosphonates like Tildren can be effective when the condition is due to bone degeneration. Drugs like these work on a cellular level to maintain or increase bone integrity by slowing down bone loss and encouraging bone growth. Stem cell treatment is also being explored as a way to reverse bone degeneration.

Surgery is sometimes recommended when other treatments are no longer enough to keep the horse comfortable: a digital neurectomy, where the digital nerve in the pastern is cut, has been shown to eliminate pain in the affected foot. It should be noted, though, that although the pain disappears, the underlying condition will still be present, and should be taken into consideration when creating an exercise plan.

There’s no cure, and eventually most horses become unresponsive to treatment and need early retirements, but with early diagnosis and proper management, it’s possible to keep horses active and comfortable longer than ever before.

 

Cindy McMann

image: clarita (MorgueFile License)