Navicular syndrome, a condition known for 2,000 years, is an inflammation of the navicular complex—a functional unit comprising the navicular bone, the navicular bursa, and the deep flexor tendon.
To truly understand navicular syndrome, it is first and foremost important to understand the anatomical structure of the hoof joint. Riders often say, “My horse is lame; it has a navicular issue.” Strictly speaking, however, every horse has a navicular. This term actually refers only to the functional unit consisting of the navicular bone, the navicular bursa, and the deep flexor tendon. The navicular bone is a small, elongated bone shaped like a weaver’s shuttle, located transversely at the back of the hoof joint beneath the deep flexor tendon. Between the tendon and the navicular bone lies the navicular bursa, a small fluid-filled sac designed to prevent pressure and friction between the tendon and the bone.
Although navicular syndrome has been known since the domestication of the horse, not all of the factors leading to its development have yet been fully elucidated. Since navicular syndrome does not occur in wild horses, it is considered certain that in riding horses—and especially in sport horses—the specific stress they endure leads to wear and tear and inflammation of the bursa. This results in tendons and bones no longer being adequately protected. Conversely, changes in the navicular bone can also lead to inflammation of the bursa.
Contributing factors to the condition include defects or abnormalities in hoof shape, toe and limb alignment, and the toe axis. Errors in husbandry, feeding, and rearing can also influence the development of podotrochlosis, as even young horses that have never been ridden or shod can develop the condition. A genetic predisposition is assumed. Hereditary transmission has not yet been confirmed. Nerve compression in the area of the seventh cervical vertebra is still being discussed, as this can lead to reduced blood flow to the forelimb and thus damage to the hoof roll.
There are various theories regarding the exact cause of navicular syndrome. Some researchers suggest that blockage of blood vessels in the toe leads to necrosis (death) of bone cells. This necrosis is visible on X-rays as balloon-like changes, known as "lollipop lesions."
On the other hand, it is hypothesized that increased pressure from the deep flexor tendon on the tendon gliding surface of the navicular bone triggers increased remodeling processes in the bone, leading to the lesions described. To date, there is no uniform scientific confirmation for either of these theories.
The condition develops gradually, which is why early symptoms are often overlooked or go unrecognized. Owners often do not notice acute lameness, but rather a flat, shorter, or increasingly dull gait in their horse. This is because, in the majority of cases, both front hooves are affected. Some horses show obvious pain when turning, while others are so subtly lame that the movement disorder is only noticeable on hard surfaces. When riding, noticeable symptoms may even improve after the warm-up phase. In a standing horse, alternating weight-shifting can be observed as the horse shifts its weight onto the front hooves. This abnormal weight-bearing can lead to visible changes in hoof shape, including, for example, pronounced heel tightness and sole bulging.
If you notice a prolonged movement disorder or the changes described above in your horse’s hoof, consult a veterinarian. A comprehensive lameness examination by an experienced equine veterinarian is essential for an accurate diagnosis.
The veterinarian will closely examine your horse while standing, in motion, and possibly also under the rider, and will perform specific tests such as a flexion test. Various tools are available for further examination. Using what is known as conduction anesthesia, the affected area on the horse’s leg can be pinpointed. In this procedure, a local anesthetic is injected into the nerves running along the leg, and the horse is then asked to trot so the veterinarian can assess whether the lameness has improved or even disappeared. The affected area can also be narrowed down by anesthetizing the fetlock joint or the bursa, or by measuring the pressure in the fetlock joint and the navicular bursa. The region of pain thus localized can then be examined more closely using specialized X-rays. In cases of navicular syndrome, it is often observed after nerve block anesthesia that the lameness “shifts.” This means that after the more severely affected leg has been anesthetized, the horse becomes lame on the less affected side. X-rays reveal changes in the bone substance of the navicular bone or other underlying bone abnormalities.
Other, but far more complex, diagnostic methods include computed tomography and scintigraphy (see the corresponding articles). Both methods can be useful if a clear diagnosis could not be made beforehand.
Once the diagnosis has been confirmed, your veterinarian will work with you to develop an appropriate treatment plan. Since the condition itself is incurable, treatment should always aim to halt or at least slow down the destructive processes in the bone, as well as to relieve pain. Your veterinarian must work closely with your farrier, as medication therapy can only achieve the desired results with appropriate orthopedic shoeing. The shoeing must be designed to facilitate your horse’s roll-off and relieve pressure on the deep flexor tendon. Depending on the severity and cause of the condition, your veterinarian may also inject special medications directly into the hoof joint or the bursa. Joint or bursa lavage may also be appropriate in some cases. However, for safety reasons, these procedures should be performed at a veterinary clinic whenever possible.
Furthermore, various surgical methods have been developed, the benefits of which are not without controversy. Some procedures lead exclusively to pain relief, while others result in improved blood flow through vasodilation. Which method is appropriate in which case always depends on the degree and severity of the condition and should be employed by your veterinarian only after extremely careful consideration.
A complementary, targeted exercise program is at least as important as the therapy itself. Avoiding tight turns and maintaining good gait mechanics are particularly important here. Discuss with your veterinarian which medications should be used for your horse and what the individual exercise plan should look like.
The wide variety of therapeutic approaches and surgical techniques highlights just how complex navicular disease is and that there is no “one-size-fits-all” treatment. For this reason, a thorough veterinary examination and diagnosis are of the utmost importance before any treatment is initiated.
If significant bony changes have already been detected in the navicular bone, a complete recovery is no longer possible. The goal of treatment by your veterinarian, in close collaboration with your farrier, should therefore always be to restore the function of the hoof roll as much as possible. With the help of state-of-the-art diagnostic and treatment methods, this is already quite possible in many cases of podotrochlosis.
Since the causes of the disease have not yet been fully understood, it cannot be completely prevented. However, you can positively influence many of the factors that contribute to its development.
The following points are particularly important:
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