Description

The navicular bone is a small bone in the foot of the horse that is subject to tension from the deep flexor tendon. It is held in place by ligaments that are part of the dense connective tissue of the bone surface and that stretch to adjacent bones.

As the coffin joint flexes, the deep digital flexor tendon glides against the navicular bone. The navicular bone is a shock-absorbing structure. During concussion, it works to transfer the load from the digital cushion to the short pastern bone.

Because of its location within the hoof structure, fractures of the navicular bone are rare. When they do occur, these fractures usually lead to sudden lameness.

Symptoms

• Sudden lameness
• Horse refuses to stand on affected hoof
• Sudden change in gait favoring injured limb

Causes

Navicular fractures occur most often when a horse kicks a stationary object, such as a post or wall. Fractures may also be caused by an accident involving the foot that puts unusual pressure on the hoof and foot structure, including the coffin bone, the tendons, and ligaments.

Prevention

Preventing navicular fractures is best accomplished with good horse management that prevents horses from engaging in activities that might lead to fractures or other injuries.

Treatment

Although surgery may be used to correct a navicular bone fracture, most veterinarians and farriers recommend a conservative approach, including rest, careful trimming of the affected hoof, and sequential scheduling of special shoeing efforts to correct the fracture and bring the horse back to serviceability.

Following a diagnosis of navicular fracture, the affected hoof should be trimmed to its normal hoof pastern axis. Some veterinarians recommend a Patton bar shoe to raise the anterior hoof wall to just below vertical alignment. This helps eliminate forces on fragments of the bone by the deep digital flexor tendon.

Leather pads may also be used to arrive at the best position for the particular hoof structure. Usually stall rest for 60 to 90 days is necessary for the bone to heal properly.

Short periods of hand walking can begin once it is confirmed that the bones have healed. The shoes are reset approximately every four weeks, with pads being removed to the point where the horse can be shod normally. Bute is often recommended by veterinarians to relieve inflammation and pain from the injury.

In some cases, Palmar digital neurectomy may be an option. However, results have been poor and the procedure may cause more problems than it addresses.