Horse owners dread the diagnosis of navicular syndrome. Much new research has focused on this disease. To help understand whether there is a cause for concern, this month’s blog post will help clear up some myths and illuminate the facts surrounding this disease.
The most common sign of this syndrome is lameness. Sometimes there is an obvious lameness in one limb or, when both front limbs are affected, a general shortening of the stride. The front limbs are the most commonly affected.
To diagnose this disease, our veterinarians will observe the horse’s gait in-hand in a straight line and on circles, often on different footings, and sometimes under saddle. Careful palpation of the limb, hoof testers (metal instruments used to squeeze on the hoof) and flexion tests are also used to localize the lameness. When diagnosing any lameness, nerve blocks (numbing the nerve that innervates a particular region) provide our veterinarians with more conclusive evidence to localize the pain of lameness. Horses with navicular syndrome will improve when their heel is numbed.
We can’t talk about this disease without discussing anatomy. Navicular syndrome refers to pain coming from the heel region. Hence, the technical term for this disease is caudal (scientific term for towards the tail) heel pain. There are many important structures in the heel region that can contribute to this disease. The navicular bone is a small boat shaped bone (“navicu” means small boat in Latin) and has a small fluid filled pocket, the navicular bursa, which provides lubrication for the deep digital flexor tendon to glide over the bone. The deep digital flexor tendon runs down the back of the horse’s leg, around the navicular bone, and inserts on the largest bone in the horse’s hoof, the coffin bone. The navicular bone also has several ligaments that hold it in place. Any inflammation, tears, or scar tissue to these tendons, ligaments, or bursa can cause heel pain. Changes to the navicular bone – spurs, bruising, fractures, damage to the cartilage, or holes in the bone also cause pain. Long term prognosis is depends on which structure is affected.
Navicular disease used to be attributed to bony changes in the navicular bone seen on radiographs. Now we know many of the soft tissue structures in the heel can cause the pain of this disease and the name has changed from “disease” to “syndrome.” As with any therapy, treatment is most successful when we know exactly what structure is painful. The challenge with navicular syndrome is determining which structure is painful. This area is located in the hoof capsule and difficult to image. Changes to the bone can be visible on radiographs, but the only way to visualize the many soft tissue structures is with ultrasound (fairly inaccurate) or MRI. MRI is the best modality to image this area, but is expensive and requires general anesthesia for the best images.
Treatment is based on the source of pain. The most common treatment is shoeing changes, which are based on the horse’s conformation and radiographs. It can take up to two weeks to see the full effect of any new shoes, so be patient. Sometimes anti-inflammatories, such as bute, are also used, though if you are showing, be aware of USEF rules. Injecting anti-inflammatories (steroids) directly into an inflamed navicular bursa or the coffin joint (a nearby joint) also affords relief to some horses. Bisphosphonates (Osphos and Tildren) are a class of drugs that alter bone metabolism and are also used for some types of navicular syndrome. For horses with chronic pain, a surgical procedure where the nerves that innervate the heel are severed, may be recommended. This procedure is also known as “nerving”. This isn’t a permanent solution – the nerves may grow back, and requires daily monitoring to make sure there isn’t a wound on the now numb heel region.
Quarter horses, thoroughbreds and warmbloods are the mostly common affected breeds, but any horse with a long toe/ low heel, disproportionally small feet, contracted or sheared heels conformation is also predisposed.
There are some horses that navicular syndrome is athletic career ending, but with the right management, many horses perform for a long time with this disease. If you think your horse might have navicular syndrome or have any questions, please contact us.