Twitch Accessory Navicular Fracture

Overview
In an ideal situation, the navicular bone and the accessory bone will fuse together to form one bone. The problem that occurs is that sometimes the two bones do not fuse together and the patient is left with what is known as a fibrous union or basically a non solid union of bone to bone. This fibrous union is more like scar tissue and in theory can cause pain when excessive strain is placed upon it.



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
Many people have accessory (?extra?) naviculars (figure 1) - a prominent extra bone extending from the navicular bone. Most accessory naviculars are completely asymptomatic. However, some individuals will develop pain on the inside of their midfoot. Pain may occur from the pressure of the shoe ware against the prominence, irritating either the bone itself or the fibrous junction where the accessory bone meets the regular navicular. Alternatively, the fibrous junction or interface may become painful as a result of tension applied by the posterior tibial tendon through its connection or insertion at that site. Often, individuals will be asymptomatic for years, however, a new pair of good running shoes or a change in their activity level can cause symptoms. The accessory navicular itself typically develops during adolescence, when the two areas of the navicular bone fail to fuse together.

Diagnosis
Diagnosis is fairly simple based on an examination by your doctor. He or she will palpate the navicular bone, and based on the location of pain will suspect an accessory navicular. The doctor will also observe your gait to see if you are flatfooted. At this point an x-ray will make the definitive diagnosis. Other causes of pain in the same area of the foot would include a fracture of the navicular bone or possibly tendonitis or even a partial tear of the tibialis posterior tendon that inserts into the navicular. In these cases there is usually a history of trauma. People with a naturally "large" navicular bone may also develop a bursitis due to chronic shoe pressure.

Non Surgical Treatment
If symptoms have been aggravated by an increase in activity level, backing off on activities in the short term can be helpful. The foot is subject to a lot of repetitive loading during walking, and therefore minimizing this force will often help symptoms to settle. After symptoms have settled, the activity level can then be gradually increased.



Surgical Treatment
For patients who have failed conservative care or who have had recurrent symptoms, surgery can be considered. Surgical intervention requires an excision of the accessory navicular and reattachment of the posterior tibial tendon to the navicular. Often times, this is the only procedure necessary. However, if there are other deformities such as a flat foot or forefoot that is abducted, other procedures may be required.