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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. People who have an accessory navicular often are unaware of the condition if it causes no problems. However, some people with this extra bone develop a painful condition known as accessory navicular syndrome when the bone and/or posterior tibial tendon are aggravated. This can result from any of the following. Trauma, as in a foot or ankle sprain. Chronic irritation from shoes or other footwear rubbing against the extra bone. Excessive activity or overuse. Many people with accessory navicular syndrome also have flat feet (fallen arches). Having a flat foot puts more strain on the posterior tibial tendon, which can produce inflammation or irritation of the accessory navicular.





Causes

Accessory navicular syndrome as it is called can result from a number of causes, excess or overuse syndrome as seen in an athlete. Trauma to the foot as in an ankle sprain or direct trauma to the navicular bone. chronic irritation from shoes rubbing against the extra bone, over time, may cause pain. Excessive pronation which strains the attachment of tibialis posterior muscles into the navicular bone. Keep in mind, the larger the actual accessory bone, the greater the chance of it becoming an issue.


Symptoms

The catalyst for symptoms might be some sort of injury (such as a broken or sprained ankle), excessive activity, or irritation from where shoes are rubbing on the bony prominence the accessory navicular makes. These can irritate the bone, or make the tendon it?s embedded in (the posterior tibial tendon, remember?) inflamed and sore. Because the tendon is compromised in its ability to support the arch, accessory navicular syndrome almost always leads to flat feet, which is one very obvious symptom.


Diagnosis

During your clinical exam, you may note erythema to the navicular prominence area and a foot that collapses in stance. While it?s common to see flat feet with these patients, this may not always be the case. You will note a significant difference in the off-weightbearing arch compared to the foot in stance, which is lower. These patients will always have pain to the navicular bone, especially at the major insertion of the posterior tibial tendon just proximal and also inferior to the navicular bone. You may also find they have pain on resisted adduction.


Non Surgical Treatment

The foot may be placed in a cast or removable walking boot to allow the affected area to rest and decrease the inflammation. Physical therapy including exercises and treatments to strengthen the muscles, decrease inflammation, and prevent recurrence of the symptoms. Custom orthopedic devices that fit into the shoe providing arch support. Even after successful treatment, symptoms may reappear.





Surgical Treatment

If conservative measures do not seem to help, however, you may need to have surgery to make adjustments to the bump. This could include reshaping the little bone, repairing damage to the posterior tibial tendon, or even removing the accessory navicular altogether.