New Diagnostics Help Decipher Navicular Pain

One of the most exciting aspects of Sport Horse Medicine recently is the work being done with diagnosing lameness that involves the back half of the foot in equine athletes. This means deciphering all the anatomical structures in the region that may be potentially injured, identifying the injury to the structure and then applying an appropriate treatment that is most likely to return the horse to competition.

Historically, the area of the back part of the foot has been dominated by the navicular bone, and yes, this is a vital structure in that area. Horses that had intermittent lameness; pointing a foot; soreness to hoof testers over the frog; shifting leg lameness; contracted, upright feet; and stabbing toes, shortened stride movement were candidates for Navicular Disease. If the veterinarian could improve or alleviate the lameness by "blocking the heels" of the foot, this gave added confidence to the idea that the navicular bone was the cause of the problem. Usually, radiographs may or may not further incriminate the navicular bone. Then treatment was instituted to relieve stresses on the bone, or other structures in the region, often with varied success.

Recently, with the advent of improved and innovative diagnostic modalities for the horse, veterinarians are better able to truly define the structure(s) injured, the type of injury, severity of the injury and thus, have a better idea of the prognosis to return to the previous level of activity. This means injury to the back part of the foot can be better categorized and hopefully treated more effectively.

Some of these diagnostic tools are improvement in existing technology, better understanding by veterinarians of the findings or new technology adapted for use in the equine athlete.

Radiographs (X-rays) have long been the standard to evaluate the bones of the foot, and especially the navicular bone region. The new digital and computed radiographic equipment has provided greater detail, which allows more precise evaluation of structural changes in the bones of the foot. This new technology can pick up bone remodeling in response to stress, small changes along bone edges that were not as easily visible previously, recent bone lay down or proliferation, early calcification of soft tissues (ligaments, tendons) and a better visualization of bone lysis or reabsorption. In addition, because it gives sharper margins to bones, interfaces of bony surfaces and joints can be better evaluated for problems.

Diagnostic ultrasound has improved dramatically for equine practitioners in recent years, which allows better visualization of the soft tissue structures in the back of the foot.

The flexor tendons, navicular bursa, impar ligament and even the contours of bones can be evaluated with greater certainty due to the technological advances of newer machines.

Advanced training and continuing education has provided veterinarians the skills to detect and appreciate subtle changes that cause lameness issues. Ultrasound is being used as a guide to better place treatments in a specific structure of the back of the foot, also.

The use of nuclear scintigraphy ("bone scan") has upped our understanding of the physiologic activity of structures in the back half of the foot. By using injected radioactive material, a big geiger counter and a computer program, we can determine what structures are inflamed or damaged. Injured tissues are more metabolically active. By finding these "hot spots" and knowing the anatomy of the area, we can get a good idea which structure is involved as well as the possible nature of that injury. This undoubtedly allows for more precise treatment of that structure.

The latest tool to help decipher "pain in the back half of the foot" in horses is magnetic resonance imaging (MRI). This has opened new doors for veterinarians involved in diagnosing and treating lameness. Both "low-power" standing horse and "highpower" recumbent horse machines are available. This technology develops images of structures based on magnetic properties of tissues and sophisticated computer analysis. These images can reveal subtle changes in tissue structure, swelling of tissue, changes in density, edema and other indications of tissue injury or abnormalities. Injury that may not show up with xrays or ultrasound may be highly visible with MRI.

What all this means is that veterinarians are better able to fully define the structure and type of injury to that structure in the back half of the foot of that horse. This will allow a more appropriate treatment plan to be developed for that specific injury.

Injury to a developing bone cyst in that region may be treated differently than injury of a tendon fiber tear which may be treated differently than desmitis of the impar ligament. The specific treatment for the known problem will allow the horse a better chance to return to regular competition.

So, "pain in the back of the foot" is not just navicular disease anymore.

Article courtesy of The Kentucky Equine Education Project (KEEP), www.horseswork.com.

About the Author

Duncan Peters, DVM, MS

Duncan Peters, DVM, MS, Dipl. ACVSMR, ISELP, is the co-owner and founder of East-West Equine Sports Medicine and focuses his practice on locomotor pathology and the diagnosis, treatment, and management of sport horse health for optimum performance. A University of California, Davis, graduate, Peters has also served as as director of the Clinical Equine Sports Medicine Program and associate professor of Large Animal Clinical Sciences at Michigan State University’s College of Veterinary Medicine. An FEI veterinarian, he was member of the 2010 Alltech World Equestrian Games' veterinary commission. Peters is an active horse owner and competes hunter-jumpers.

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