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Overview

The accessory navicular (os navicularum or os tibiale externum) is an extra bone or piece of cartilage located on the inner side of the foot just above the arch. It is incorporated within the posterior tibial tendon, which attaches in this area. An accessory navicular is congenital (present at birth). It is not part of normal bone structure and therefore is not present in most people.





Causes

Just having an accessory navicular bone is not necessarily a bad thing. Not all people with these accessory bones have symptoms. Symptoms arise when the accessory navicular is overly large or when an injury disrupts the fibrous tissue between the navicular and the accessory navicular. A very large accessory navicular can cause a bump on the instep that rubs on your shoe causing pain.


Symptoms

The symptoms of accessory navicular syndrome commonly arise during adolescence, when bones are maturing and cartilage fuses into bone. In other instances, symptoms do not appAccessory Navicularear until adulthood. The signs and symptoms include a visible bony prominence on the midfoot the inner side of the foot above the arch. Redness or swelling of the bony prominence. Indistinct pain or throbbing in the midfoot and arch during or after physical activity.


Diagnosis

Usually, you will only need an X-ray to determine the size or type of the accessory navicular bone or the amount of medial navicular tuberosity hypertrophy. Be cognizant of stress fractures which may be duplicated as a hairline fracture or increased calcification. When treating children, always look for avascular necrosis of the navicular (Kohler?s disease). An X-ray of this condition will reveal a flattening of the navicular along with increased bone density.


Non Surgical Treatment

The goal of non-surgical treatment for accessory navicular syndrome is to relieve the symptoms. The following may be used. Placing the foot in a cast or removable walking boot allows the affected area to rest and decreases the inflammation. To reduce swelling, a bag of ice covered with a thin towel is applied to the affected area. Do not put ice directly on the skin. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen, may be prescribed. In some cases, oral or injected steroid medications may be used in combination with immobilization to reduce pain and inflammation. Physical therapy may be prescribed, including exercises and treatments to strengthen the muscles and decrease inflammation. The exercises may also help prevent recurrence of the symptoms. Custom orthotic devices that fit into the shoe provide support for the arch, and may play a role in preventing future symptoms. Even after successful treatment, the symptoms of accessory navicular syndrome sometimes reappear. When this happens, non-surgical approaches are usually repeated.





Surgical Treatment

If non-surgical treatment fails to relieve the symptoms of accessory navicular syndrome, surgery may be appropriate. Surgery may involve removing the accessory bone, reshaping the area, and repairing the posterior tibial tendon to improve its function. This extra bone is not needed for normal foot function.