NAVICULAR SYNDROME

Navicular syndrome affects the navicular bone and associated structures in the foot. The navicular bone is a small bone, which lies across the back of the coffin joint within the hoof. The deep digital flexor tendon runs over the lower surface of the navicular bone and inserts on the bottom of the pedal bone and contracts to flex the foot.
Diagnosis is based on a combination of history, clinical signs, nerve blocks and radiography.

Navicular problems affect the front feet of horses causing a low grade, often bilateral lameness. It is usually slowly progressive and lameness may be worse when the horse is exercised on hard ground. Affected horses may place the toe down first, to avoid putting weight on their heels and this may cause them to stumble. The lameness is usually worse on the inside leg when the horse is trotted in a circle.

Injection of local anaesthetic (nerve block) around the nerves to the back half of the foot will often relieve the lameness associated with navicular syndrome. Some cases improve when the coffin joint is blocked with local anaesthetic.

X-rays may reveal damage to the navicular bone but bone changes can be difficult to interpret as the significance of some changes is unknown. Navicular syndrome can exist without obvious radiographic changes.

Navicular syndrome can sometimes be managed effectively. Corrective trimming and shoeing is important to ensure foot balance. The horse should be shod to ensure ease of break over at the toe and good heel support. Medication such as phenylbutazone will help relieve pain, however its use is not without potential hazard. Some horses can be treated with intra articular (coffin joint) medication (e.g. cortisone).

Reviewing the amount and type of work the horse performs as well as taking care with work surface can help. In the past warfarin, aspirin and isoxsuprine have all been used in the treatment of navicular disease. However, recent studies suggest these agents have little, if any, effect on the syndrome.

Cutting the nerves to the heel (neurectomy) can provide relief of pain however, this should be considered as a last resort if other methods are unsuccessful. Postoperative complications may occur and include rupture of the deep flexor tendon, painful inflammation of the cut nerve endings (neuromas) and damage to the foot, which goes unnoticed. Also, neurectomy alone does nothing to slow the process of degeneration

Maintaining good foot balance can help ensure optimal foot function, however not enough is understood about navicular syndrome to guarantee prevention