Chronic pain in the back third of the horse’s foot is the hallmark of navicular syndrome, a common cause of lameness and one that’s frustrating for horse owners and veterinarians alike. But presentations at last winter’s American Association of Equine Practitioners annual convention in Salt Lake City, Utah, showed how better diagnostic tools and new treatments are changing the picture.
The importance of understanding the exact cause of heel pain was highlighted by Santiago Gutierrez-Nibeyro, DVM, an equine surgeon at the University of Illinois. Although degeneration of the navicular bone, which underlies the heel, was once blamed for this condition, the bone is just one of several structures that can cause sore heels. For example, in some cases the deep digital flexor tendon, which passes over the navicular bone, is inflamed.
Dr. Gutierrez-Nibeyro reviewed cases in which specific lesions were identified with magnetic resonance imaging before the horse underwent palmar digital neurectomy, or nerving. In this surgery, an option when horses don’t respond to medical treatment, the surgeon cuts the palmar digital nerves, deadening feeling at the back of the foot to keep the horse comfortable and extend his working life. But nerving isn’t always successful, and the effects aren’t permanent.
Of 50 horses in this study, 46 improved after surgery and 40 were able to return to their previous level of work for an average time of 20 months. But horses with certain types of damage to the DDFT—core or linear lesions—didn’t do so well. Their lameness often didn’t resolve or, if it did, returned more quickly. Nerving is not a good option for all horses, Dr. Gutierrez-Nibeyro concludes, so it’s important to identify the precise cause of soreness with an MRI before scheduling surgery.
Separately, veterinarians Kent Allen, DVM, of Virginia Equine Imaging, and Valentine Williams, DVM, of Ceva Animal Health, reported on clinical trials for Tildren (tiludronate disodium from Ceva), one of two drugs that the U.S. Food and Drug Administration approved in 2014 for controlling the clinical signs of navicular syndrome. The other new drug is Osphos (clodronate disodium from Dechra, Ltd). Both Tildren and Osphos are biophosphates, drugs that slow the process of bone remodeling and are commonly prescribed to prevent bone loss in people. European vets have been treating navicular horses with biophosphates for more than 10 years, but their use in the U.S. was previously off-label. FDA approval is bringing the drugs into wider use.
The Tildren trials involved 181 horses diagnosed with navicular syndrome based on lameness, palmar digital nerve blocks, X-rays and MRI scans showing signs of degeneration in the navicular bone but no major soft-tissue lesions. Corrective shoeing was done for all the horses; 119 received a single tiludronate treatment (by IV infusion) while the rest received a placebo. The drug was judged effective—64 percent of horses who got it improved at least one grade on the lameness scale used by the AAEP, compared to 48 percent of horses who had only corrective shoeing. The most common side effect was mild colic, which cleared up with hand-walking in most cases.
This article originally appeared in the June 2015 issue of Practical Horseman.