Navicular syndrome

Even if the term navicular disease is commonly used in the equine world, the exact term for the disease is « podo-trochlear syndrome » or podotrochlosis. It corresponds to pain which concerns the navicular bone and the surrounding structural tissues, which together make up the podo-trochlear system.

The clinical signs of  podotrochlosis are pain during distal inter-phalangeal extension, which is utmost when the limb is behind the vertical. Indeed, in this position pressure exercised on the podotrochlear apparatus is the greatest : the deep digital flexor tendon is extended, and puts pressure on the navicular bone, provoking pain.

Any of the stuctural element s of the apparatus may be affected, separateley or at the same time, with for example:  
•    Damage to the navicular bone : fracture, osteolysis (destruction of bone tissue), sclerosis (thickening of the contours of the bone), presence of osteophytes (bony projections or exostoses on the surface of the bone) ;
•    Damage to the deeep digital flexor tendon : tendinitis (inflammation of the tendon)
•    Damage to the navicular bursa : bursitis (inflammation of the bursa)
•    Damage to the ligaments : desmitis (inflammation of a ligament), presence of enthesophytes (bony projections at the attachment of the bone and the ligament).
This affliction concerns more specifically Quarter horses and Warmbloods.

When working, chronic lameness appears insidiously, with different phases and varying degrees of pain. Strides seem to be shorter, specifically in the posterior phase of the stride (when the limb is extended towards the rear) is shortened. This lameness will also frequently be more obvious on hard ground, or on a circle, on the inside leg (if the pain is located in the right foot, the horse will be lamer when on a right hand circle). The specificities of the lameness can also be different depending on which structural element is affected : in the case of damage to the navicular bone, lameness will be more obvious on hard ground, whereas damage to the soft tissues will result in greater lameness on soft or warm ground.

A clinical examination consists in a static examination (at rest) and a dynamic examination :

The wedge test consists in placing the horse’s hoof at the end of a board, having the other front limb held up by a helper. The board is then progressively lifted at the opposing end so as to force the podotrochlear system into a hyperextended position. This will provoke signs of pain in the horse (lifting his head, shaking, or jumping off the board). Interpreting this test remains delicate when testing young or anxious horses.

Anaesthetising the distal part of the hoof can be carried out, after ascertaining from radiographs ( X-rays)  the absence of a fracture. If lameness is lessened after the local anaesthetic, this shows the pain is located in the distal area of the hoof, but does not lead to concluding with certainty that there is presence of podotrochlosis. Once one foot is anaethetised, it is fairly frequent to notice similar lameness in the other limb. This disease frequently affects both legs, but can be more marked on one front limb, which hides the lameness in the other.

Two imaging techniques are then associated : X-ray (to observe the navicular bone) and an ultrasound scan ( to observe the soft tissues).
An MRI scan (Magnetic Resonance Imaging) is the most reliable examination : it gives an accurate and overall assessment of the entire area. This technique is costly, and not very widespread in some regions.

Treatment is variable according to severity of the clinical signs, the tissues affected, the damage observed, and the horse’s workload. The purpose is to relieve the horse by lessening the pain. Treatment cannot however cure the horse : this affliction is degenerative, and will worsen over time.
In the case of extreme lameness, the horse should be turned out to rest to allow the inflammation in the soft tissues or the remodelling of the navicular bone to lessen.

Putting in place adapted shoeing is of prime importance and aims to reduce pressure and tension on the podotrochlear apparatus.

The purpose is therefore :
•    To encourage breakover (by decreasing the coverage of the shoe in the toe area, and adding a rocker effect by bevelling the shoe in the toe and medial areas so as to reduce the front  leverage ;
•    To support the heels (by increasing the weight-bearing surface in the heel area).

Two types of shoe may be used :
•    The « egg bar shoe » : oval shaped shoe, bevelled on the sides
•    Using reverse shoes (Napoleon shoes).

Good collaboration between farrier and veterinarian is of prime importance.

Medical treatment can also be implemented :

Numerous other treatments are available (surgical treatment, acupuncture, shock wave therapy….) according to the type of damage observed, but further studies need to be carried out to demonstrate their effectiveness. To date there is no set standard treatment for podotrochlosis.

The horse’s activity should also be managed and adapted, by favouring supple soft surfaces, and lengthy warm-ups. Circles are banned, especially on the hand where the foot is affected. Using studs should be avoided as they block the foot.