The name makes many a horse owner shudder as they think over stories of friends’ experiences or their own with “navicular” horses. But what is navicular disease? And is it always a life sentence of lameness?
To answer these questions, you first need a trustworthy veterinarian on your side to help you through any lameness your equine partner experiences. Veterinarians’ findings through diagnostic imaging (radiography, ultrasonography and/or MRI) and diagnostic nerve blocks are of the utmost importance for diagnosing this condition. Secondly, you should know some basic terminology, so you understand your veterinarian’s findings.
Anatomy of Navicular Apparatus
Navicular disease or navicular syndrome is an abnormality or inflammation of the back of a horse’s foot, specifically the navicular bone and its adjacent tendon, joint and bursa. The navicular bone is a small bone in the horse’s foot that sits between the coffin joint and the flexor tendons. The navicular bursa is the synovial structure that sits between the navicular bone and deep digital flexor tendon. This bursa helps the deep digital flexor tendon smoothly glide across the back of the navicular bone. The deep digital flexor tendon runs behind the navicular bursa and under the coffin bone, attaching at its tip. The “navicular apparatus” is a term that describes all of these structures, as well as other small ligaments in the area, and their relationship to one another. The term “navicular syndrome” implies abnormalities or inflammation of one or more pieces of this apparatus.
Signs of Navicular Disease
Navicular disease (or syndrome) might first appear as a slight head bob in your horse or a decrease in expected performance. Your veterinarian might identify signs of heel pain with a hoof tester exam and/or a noticeable limp when your horse tracks in a circle. As with most lameness conditions, there is variability in how this abnormality presents in your horse.
Your veterinarian also may perform diagnostic nerve blocks to localize the pain to the foot. By desensitizing these nerves with a numbing agent, the limp should go away. Frequently, once the lame foot is blocked, the horse goes lame on the other foot. This is because many horses have navicular syndrome affecting both front feet, but one is more significant than the other, thus showing a primary lameness on one foot.
Your veterinarian also will likely take radiographs or X-rays to help diagnose this condition. It is possible for a horse to have radiographic changes consistent with navicular syndrome before they have clinical signs of lameness. It is uncommon for a horse to have radiographic changes consistent with navicular syndrome and not have lameness associated with those changes at some point in their lifetime.
Predisposition to Navicular Syndrome
There is no proven genetic heritability to navicular syndrome, although there are predispositions due to breed, conformation, discipline and training. Navicular syndrome is intensified by concussive forces to the apparatus. Big-bodied but small-footed horses like Quarter Horses, horses with long toes like Thoroughbreds and horses with upright pasterns all may have conformation predispositions. Disciplines that require large concussive movements like jumping or that require consistent intensive work can predispose horses as well. Starting a high level of training and/or work on a young horse also can contribute to their predisposition. The onset of navicular syndrome typically occurs between ages eight and 14 years old, but it can occur outside of this range.
Navicular syndrome can present with a wide range of severity. In a mild case, a horse may have inflammation in the coffin joint or navicular bursa. In these cases, corrective shoeing and joint injections may help significantly. Some may be maintained just with anti-inflammatories like phenylbutazone or “bute” and appropriate shoeing. In a severe case, the concussive forces can cause changes to the navicular bone that can be incredibly painful for the horse. These severe cases sometimes can be managed with joint injections and corrective shoeing but can require more intensive therapies such as stall rest, which is similar to bed rest for your horse; bisphosphonate drugs that help repair bone; and even neurectomies (surgical removal of a portion of the nerves to the foot) for the horse to be comfortable. Severe cases are almost always performance-limiting, and because of this, these horses typically have a lower resale value than a normal horse.
Navicular syndrome is typically a progressive disease, and most horses will become more lame and increasingly difficult to manage over time. Some horses can continue at their original level of performance after this diagnosis for years, and some horses decline rapidly. Finding the right mix of corrective shoeing, anti-inflammatories, joint therapies and a balance of rest and work can help some of the affected horses have productive lives, whether it be in a show pen at a high level of performance or in a pasture.
Co-Author: Darby Sherrod Horne, DVM
Marcus Hutka, MS, DVM, is a graduate of Texas A&M College of Veterinary Medicine who lives in Navasota, Texas. Dr. Hutka practices at Equine Partners Veterinary Services in Navasota, Texas.