By Shirley Byers

If you have ever experienced the relief that comes after exchanging ill-fitting shoes for a more comfortable pair, you can understand what a horse suffering from navicular disease feels like when it gets a set of corrective shoes.

Corrective shoes are not a cure-all for navicular disease, but they’re the first line of defence for this chronic cause of foreleg lameness, says equine surgeon Dr. Joe Bracamonte.

“When I diagnose navicular syndrome, the first thing I do is try to find the shoe that fits that horse. One of the things that’s going to improve his life is finding that shoe,” says Bracamonte, an associate professor at the Western College of Veterinary Medicine (WCVM) in Saskatoon, Saskatchewan. 

“Navicular syndrome is a degenerative disease. It’s not like we can stop it. What we’ve got to do is try to slow it down.”

Bracamonte estimates that about 70 to 80 percent of the horses that come to the WCVM’s Veterinary Medical Centre because of lameness issues are suffering from this degenerative condition of the navicular bone and soft tissues in the back of a horse’s forefeet.

Internal Hoof Structure

Photo (above): Cutaway comparisons of a healthy foot and an unhealthy foot. Note the difference in the size of the digital cushion below the DDFT and the navicular bone. Photo courtesy of Cole Henderson

As researchers have gained a greater understanding of the disease, it has gone through several names over the years. Navicular disease is now known to be caused by a variety of abnormalities and is referred to as “navicular syndrome” or “caudal heel pain.”

This condition shows up in horses aged anywhere between four and fourteen years old. In North America, navicular syndrome affects mainly Thoroughbreds and other breeds such as Quarter Horses and Tennessee Walking horses. Ongoing studies will eventually confirm whether a predisposition to developing navicular syndrome is a heritable trait in some breeds.

Bracamonte explains that foot care is very important for all horses, especially for Quarter Horses that have small feet — a predisposing factor for navicular syndrome. As well, this breed’s tendency for long toes and underrun heels could put stress on the navicular area.

Other common predisposing factors for the disease include a broken forward or backward hoof axis, sheared heels, contracted heels, and mismatched hoof angles.

Clinical Signs and Diagnosis

Horses with navicular issues likely present with “on and off” lameness until one day, the animal is suddenly acutely lame. Stiffness is another clinical sign, points out Bracamonte.

In barrel racing horses, riders might notice a gradual loss of performance and a reluctance to turn. Western pleasure horses might also favour a shorter stride.

A common misconception is that lame horses have shoulder issues, but that’s usually not the case. “For every case of lameness originating in the shoulder, we see 2,000 that are foot related,” says Bracamonte.  

To diagnose navicular syndrome, he wants to see his equine patients trot on a hard surface, and in a circle on hard and soft surfaces. “We have a grading system from zero to five,” explains Bracamonte. “Five is non-weight bearing.”

Photo (above): Horses with navicular issues may be stiff and sporadically lame. A horse used for barrel racing might exhibit a gradual loss of performance and a reluctance to turn. Photo: ©CanStockPhoto/DGPhotography

“It almost seems like they’re stepping on eggs,” says Bracamonte. 

Horses with soreness in both front feet present with an even choppier gait. On a hard surface, they’re very careful how they place their feet. There could be stiffness in their necks, and in most cases, one foot is more painful. Horses suffering from navicular disease often have a short stride in both limbs, and they might swap lame legs when navigating tight circles or corners.

To determine which leg is in worse condition, Bracamonte explains that he might apply stress to certain areas of the horse’s legs. For example, he might pick up one leg so more weight rests on the other leg, then release the leg and watch for an increase in lameness as the horse moves.

Photo (above): To diagnose navicular syndrome, the horse is observed trotting on a hard surface, and on a circle on both hard and soft surfaces. Photo: ©Shutterstock/Ulrich Willmunder

Here are two other tests used by veterinarians to diagnose navicular syndrome:

• Wedge test: A veterinarian places one of the horse’s front feet on a wedge of wood to force the limb into a hyper-extended position. At the same time, the horse’s opposite leg is held in the air. After a period of time, the horse is trotted away in a straight line so the practitioner can watch for an increase in lameness.

• Frog pressure test: A veterinarian places one of the horse’s front feet over a small block of wood (often the handle of a hoof knife or hammer). This test applies pressure on the caudal aspect of the horse’s frog while its opposite limb is held in the air. After a period of time, the horse is trotted off in a straight line so the veterinarian can watch for an increase in lameness.

Bracamonte emphasizes that these tests are not 100 percent specific for the navicular bone, so veterinarians need to interpret the results relative to other findings. Clinicians also use hoof testers to apply pressure, but Bracamonte points out that less than 50 percent of horses respond to the pressure of hoof testers. Nerve blocks can help to narrow down where the problem is occurring in the range from the horse’s foot up to its shoulder. However, Bracamonte points out that veterinarians now know that nerve blocks aren’t that specific.

Potential treatments

The prime goal of shoeing is to decrease pressure on the navicular bone. Raising the heel, usually executed with wedge pads or a wedge shoe, is the technique that best decreases pressure on the navicular area.

Photo (above): Wedges have long been used as a treatment for navicular disease to decrease pressure on the navicular area. Photo courtesy of Cole Henderson

Other shoeing options include the egg bar shoe, which increases the surface of contact and gives increased stability to the foot. Natural balance shoes, which were developed after researching horses in the wild, are also effective in treating horses diagnosed with navicular disease. 

The concept of “breaking in” new shoes applies to horses as well: “Give the horse two weeks to adapt to the shoe,” says Bracamonte. 

Injecting the coffin bone with steroids is another line of treatment. Bracamonte says the steroid’s positive effects might last four to six months after the first injection, but over time, the effectiveness of subsequent treatments will gradually decrease until there’s no response. 

Steroids can also be injected directly into the bursa (fluid-filled sac that cushions the navicular bone), resolving the lameness for an average of four months in 80 percent of horses that do not respond to standard treatments.

Tildren® (tiludronate disodium), a drug prescribed for osteoporosis, is effective for managing equine caudal heel pain because of the loss of bone density associated with this disease. Horses with mild to moderate navicular syndrome are the best candidates for this drug therapy.

If a horse is no longer responding to any other treatment, Bracamonte says a neurectomy is another option. In this procedure, an equine surgeon severs both palmar digital nerves below the base of the sesamoid bone to reduce the pain. However, this procedure must be used with extreme caution and only on horses that are carefully supervised since they’re more vulnerable to foot injuries. 

Shirley Byers is a writer and editor from Kelvington, Saskatchewan. She freelances for a variety of North American magazines and newspapers.

This article was originally published in the March 2015 issue of Canadian Horse Journal.

Main Photo: Quarter Horses are one of the breeds predisposed to developing navicular syndrome due to their tendency to have smaller feet, with long toes and underrun heels, which put stress on the navicular area. Photo: ©Shutterstock/Stephanie Coffman