NAVICULAR SYNDROME

Horses with navicular syndrome present with a forelimb lameness that may shift from one limb to the other. Occasionally these horses are lame on both front resulting in a shortened stride or a shuffling type gait. Typically the lameness is worse on firm ground or when turned and it will usually improve with anti-inflammatories and rest.

Often times owners complain that the horse stumbles frequently in front or is stiff in the shoulders. Horses with heel pain such as navicular syndrome try to land on their toe avoiding the painful heel region. As a result these horses often stub their toe and stumble. At rest some navicular horses will point one foot, placing it ahead of the other forefoot. Upon close inspection of the forefeet one foot is often smaller and contracted at the heels. This is usually a sign of chronic (long term) pain in that leg.

Because navicular syndrome is a multifactorial condition it is important to understand the anatomical components involved. The four primary structures included are the navicular bone, the deep digital flexor tendon (DDFT), the coffin joint and the navicular bursa. The primary component is the navicular bone positioned between the coffin bone and the DDFT. As a result of its location it forms the back of the coffin joint as well as providing a smooth surface for the DDFT to glide upon. The navicular bursa is a small fluid filled sac located between the back of the navicular bone and the DDFT. Its purpose is to absorb the force the DDFT imparts to the navicular bone when the leg bears weight. The final component is the coffin joint. This is a high motion joint positioned between the short pastern bone, the coffin bone and the navicular bone. Because these four structures are so intimately related damage or injury to one can affect the remaining components.

Detrimental changes in the navicular bone and the associated structures are the result of the stresses placed upon the horse's foot. Horses with small feet relative to their body size, upright pasterns low heels and long toes place more strain on the navicular bone. The concussive forces placed on the horse's foot result in inflammation and remodeling of the navicular bone which in turn affects the DDFT, the coffin joint and the navicular bursa.

Correct diagnosis of navicular syndrome requires a thorough lameness evaluation. This exam includes walking and trotting the horse both on the straight and in circles. Flexion tests, a hoof tester exam and diagnostic nerve blocks are important parts of a lameness exam. Horses with navicular syndrome will greatly improve after a palmar digital nerve block (applying a local anesthetic similar to lidocaine) over the nerves to the horse's heels. Radiographs are necessary to view the bony structures within the foot and to assess the severity of the problem in addition to suggesting the best type of treatment for that particular horse.

If a horse is diagnosed with navicular syndrome there are several treatment options. The first and foremost is to trim and shoe the horse properly based on the radiographs. Usually we will use an egg bar shoe with a rolled or rockered toe and a heel wedge. This will provide a broad base of support to reduce concussion in addition to reducing the biomechanical stresses placed upon the navicular bone. Depending on the individual case an oral medication called isoxsuprine can be used to increase blood flow to the navicular bone. Injections of medication directly into the coffin joint may be beneficial to some horses. The final and last approach to treatment is to use pain medications such as Bute or Banamine or to perform surgery to alleviate the pain.