Diagnosing Navicular Disease in Horses

Diagnosis of hoof pain in horses can be daunting for veterinarians, despite the technology available to them. According to the results of a recent study, certain radiographic techniques might help veterinarians diagnose navicular disease earlier than usual, improving comfort for affected horses.^*

While the term “navicular disease” is often used to describe any horse with heel pain, it more accurately refers to horses with degeneration of the navicular bone. The navicular bone lies nestled in a bed that cushions and protects the deep digital flexor tendon as it passes along the bone’s rear surface. Repeated concussion causes hyperstimulation of bone-producing cells, which reshape the navicular bone and affect adjacent cartilage. Remodeling does not always produce smooth bony tissue; instead, it sometimes generates minute needle-like spikes on the navicular bone. Over time, the rubbing of the deep digital flexor tendon against these spikes induces inflammation and pain.

Degeneration of the navicular bone can severely limit a horse’s performance. Clinical signs of navicular disease include a short, choppy stride with lameness that worsens when the horse is worked in a circle, as when longeing. Frequent stumbling may occur at all gaits, even the walk, or when horses are asked to step over short obstacles such as ground poles. Navicular disease typically involves the front feet. Pain may be more intense on one foot, and this can cause frequent weight-shifting or leaning to alleviate pain.

“Following full physical and lameness examinations, the most common diagnostic test for navicular disease is radiography,” explained Laura Petroski, B.V.M.S, a Kentucky Equine Research veterinarian.

A veterinarian looks for one or more radiographic changes to the navicular bone:

1. Marginal enthesiophytes, which are small bony growths at the edge of the bone that should be smooth;
2. Enlarged synovial fossae or vascular channels;
3. Formation of fluid-filled cysts in the bone due to loss of normal bone material;
4. Loss of normal bony architecture; and
5. Bony erosions and loss of a defined cortex (the outer layer of the bone).

“Skyline” radiographs help veterinarians make a diagnosis of navicular disease. Typically, these radiographs include a single shot aimed across the bottom surface of the navicular bone (approximately 55° in reference to the horizontal). Based on the research performed by veterinary researchers at Colorado State University, additional skyline radiographs taken at angles up to 35° will provide a more complete examination of the navicular bone.

“An alternate-angle navicular skyline view should be considered in addition to the standard angle skyline to investigate those cases in which flexor cortical lysis or erosion is suspected,” wrote the researchers.

In addition, the veterinarian’s ability to correctly identify navicular disease, a notoriously challenging condition to firmly diagnose, improves with additional skyline x-rays.

“Overall, observers of all levels of experience became more confident in identifying flexor cortical lysis and assessing its severity when multiple views were provided,” noted Johnson and colleagues.

“As with most chronic conditions, an ounce of prevention can save time, energy, and soundness in the long run. To that end, look for high-quality supplements specifically formulated to support skeletal tissue,” advised Petroski.

She added, “Before initiating a treatment plan, be certain to have your horse examined by a veterinarian. Navicular disease can be a nefarious condition with the ability to mimic a number of other lamenesses or even neurological conditions that present as lameness.”

^*Johnson, S.A., M.F. Barrett, and D.D. Frisbie. 2018. Additional palmaroproximal-palmarodistal oblique radiographic projections improve accuracy of detection and characterization of equine flexor cortical lysis. Veterinary Radiology and Ultrasound 59(4):387-395.