Navicular Syndrome Diagnosis

"Navicular disease is very difficult to study, because you can't reproduce it in a normal horse," said Earl Gaughan, DVM, of Kansas State University's College of Veterinary Medicine. "You can't then work backward from the disease to find a cure. The pathogenesis for navicular syndrome remains unproven, but there are some common trends."

He discussed many considerations in diagnosing the cause of heel lameness at the 15th annual Bluegrass Laminitis Symposium January 21-23, 2002, focusing primarily on identifying navicular syndrome.

These include:

  • Small hooves relative to body size;
  • Work with a torsional component (twisting forces on limbs);
  • Unbalanced hooves; and
  • Irregularly scheduled farrier care.

"Navicular" horses tend to have several common threads in their histories, including an apparent acute onset of lameness (often following a period of indeterminate poor performance), which can mimic proximal (high in the limb) lameness when viewed from the saddle that worsens with stops and turns and seems to shift from the left to the right forelimb (and vice versa). They also have a characteristically choppy stride, which results from the horse trying to land toe-first or flat (instead of the normal heel-first sequence).

Gaughan encouraged practitioners who are asked to diagnose lameness to ask owners about the horse's previous work, which can have an additive effect on the horse's feet along with his current work. Medication history and any changes in the horse's athletic expectations are also important.

Once the history has been discussed, it's time for diagnostic tests. "A perineural nerve block (of the nerve innervating the heel) is the quickest way I know of to identify heel pain," he said. Often with navicular syndrome, he said, the veterinarian will block the worst foot only to have soreness show up in the "good" foot. "If you block both sides, then the client often says, 'Now that's the horse I remember,' " Gaughan explained.

Intra-articular blocking of the coffin joint is another option, though it takes about 20 minutes for the anesthesia to fully block the joint. Intra-bursal blocking (of the navicular bursa, the cushion between the navicular bone and the deep digital flexor tendon) is more difficult, but has been thought to be very specific for a problem in that area (as opposed to a problem in the coffin joint).

However, Gaughan discussed a study that found that injecting the navicular bursa also affected the coffin joint, and vice versa. This was previously thought to be unlikely, but this study suggested that when blocking either area, a wait of only 10 minutes might result in a more specific block of that area, while waiting the customary 20 minutes might result in blocking both structures.

Further diagnostic measures might include X rays to evaluate bone structures and joints (to rule out bone spurs, etc.), scintigraphy to evaluate bone and soft tissue inflammation, ultrasonography, cinematography and thermography. "Scintigraphy is probably the one imaging modality we can hang our hats on for inflammation in the navicular region," Gaughan said. "Thermography can be useful, but remember that the image is of the skin surface-you hope that what you see on the skin is reflective of what's underneath. I think it is now and will be a very useful tool in the future." Magnetic resonance imaging and computed tomography could also prove useful when their use becomes more practical for a wide range of practices.

Treatment might include trimming, shoeing, medical therapy, and/or surgery. The goal of trimming is to balance the foot, reduce toe strain with a rolled toe, and decrease strain of the deep digital flexor tendon. Shoeing aims to increase the weight-bearing surface area (perhaps with a wide-web shoe), protect the heels (perhaps with an egg-bar shoe), ease breakover, and relieve concussion.

Medical therapy might include anti-inflammatory agents (non-steroidal anti-inflammatory drugs or NSAIDs, or local corticosteroids), synovial fluid-enhancing agents (hyaluronan or polysulfated glycosaminoglycans), or perfusion-enhancing agents (that stimulate blood flow, such as isoxsuprine, pentoxyfylline, or NSAIDs).

"Generally I save surgical treatment for cases where we've exhausted all our other options," said Gaughan. Surgical options include palmar digital neurectomy (cutting the palmar digital nerve), navicular suspensory ligament desmotomy (not very common), arthroscopic-guided bursal lavage, and distal check ligament desmotomy. The main problem with neurectomy is neuroma (an accumulation of fibrous scar tissue mixed with nerve tissue at the incised end). "Every time you cut a nerve, you get a neuroma," he explained. "The question is whether it is a painful neuroma."

The length of time before a horse becomes painful again following neurectomy varies, but Gaughan estimates an average pain-free interval of two to three years. "The success depends on how quick and clean you can do the surgery, to minimize tissue damage, and how each individual horse responds," he said.

The prognosis for a navicular horse is variable, as the disease tends to be progressive, said Gaughan. It depends on the duration of the case and response to treatment; some horses can be weaned off of treatment, while others can't. "My opinion is that navicular syndrome is not as devastating as it was previously considered to be," he concluded.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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