Navicular disease in horses is also known as Navicular syndrome. The result is the inflammation or degeneration of the navicular bone and its surrounding tissues, typically in the front feet of the horse. This disease can lead to significant or disabling lameness of a horse. The navicular bone is located between the pedal bone and the deep digital flexor tendon (DDFT). See figure 1. With an infected hoof, you can expect to see contracted width of the foot, tendon tears or necrotic appearance, and chronic inflammation of the area surrounding the navicular bone. This disease is believed to be genetic but can occur due to the conformation of the distal limbs. Structure associated with Navicular syndrome includes excessively long toes, under-run heels, and a “broken back” hoof-pastern axis. It is more common in mature riding horses (between the age of 8 and 10 years old) and is associated more commonly with certain breeds such as warmbloods, Quarter horses, and thoroughbreds.
Figure 1: Lower leg structures in the horse
Damage to the navicular bone may occur due to limited blood supply or trauma to the navicular bone. Pain and lameness can also occur in the deep flexor tendon, navicular bursa, or navicular ligaments (Carson). Typically, when a horse develops navicular disease, they will show signs through low-grade bilateral lameness. Another sign would be head-bobbing, especially at the trot. The progression of navicular disease is slow, and lameness may only be noticeable from time to time. For example, working a horse on hard ground or in a small circle may accentuate the frontal lameness of the animal. Navicular does not always occur in both hooves, and one foot may develop a harsher disease. Diagnosis is obtained by looking at the animal’s history and genetics and observing their movement. Horses that have navicular appear to place their toes down first to remove pressure from their heels.
Figure 2: Belknap, J. Navicular Disease in Horses - Musculoskeletal System
Another method to determine if a horse has navicular is nerve blocks. Nerve blocks are the injection of a local anesthetic around the nerves on the back half of the foot that surrounds the navicular bone. Once the anesthetic is applied, lameness improves. Blocking the coffin joint may also improve lameness in horses with navicular.
Veterinarians have been able to show the deterioration of the navicular bone through radiograph footage. Figure 2 shows a radiograph of navicular. Using radiographs is highly debated when determining navicular disease because some horses may not show signs on a radiograph. More recently, magnetic resonance imagining (MRI) is used to find navicular.
When looking at treatments, it’s important to remember that navicular is a degenerative disease and therefore is not curable. Most procedures are to designed to help the horse feel less pain while being worked. Phenylbutazone, an anti-inflammatory and pain reducer, is used for short periods. However, there are more permanent options available. The most effective treatment is proper shoeing designed for navicular problems. It’s essential that the horse’s hooves are balanced and land level on the ground. Broken-back or broken-forward pastern angles, under-run, or contracted heels be corrected. Typically, an egg bar shoe adds heel support. Shock-absorbing pads and wedges are used with shoes to raise the heel and remove direct pressure on the navicular bone.
Injection of the coffin joint with steroids has improved soundness in approximately one-third of horses with navicular (Belknap). However, the more effective steroid injection would be directly into the navicular bursa. A downside of the bursa injection would be the increased risk of rupturing the deep digital flexure tendon. With either of these injections, it is vital to allow the horse about three days of no forced work. The final option that is the most invasive and most permanent would be performing a palmar digital neurectomy. A neurectomy relieves all pain and prolongs the usefulness of the horse. Several complications can occur, such as painful neuroma formation, rupture of the deep digital flexor tendon, and injuries to the distal limbs with a neurectomy.
Prevention of navicular disease includes maintaining a balanced foot, heel support, and exercising the horse on the ground with sound footing. Navicular disease is not directly related to feeding practices. However, proper conditioning and maintaining adequate body weight helps with reducing strain on the hooves and tendons.
By Alex Bishop and Peggy Auwerda
The report is a project for ANS313 Exercise Physiology of Animals
- Kentucky Equine Research Staff. Navicular Syndrome in Horses - Kentucky Equine Research
- Belknap, J. K. Navicular Disease in Horses - Musculoskeletal System.” Merck Veterinary Manual
- Carson, D. M. Navicular Syndrome in Horses