Large Accessory Navicular Bone

Overview
An accessory navicular bone is a common finding on many foot x-rays. Most accessory naviculars are asymptomatic. However, in some patients the prominent bone on the inside of foot will create discomfort, which leads to difficulty with shoe fitting. Alternatively, the fibrous union between the navicular bone and the ?extra? accessory part may become irritated and cause discomfort. Diagnosis is completed through physical examination and plain x-rays of the foot. Treatment is usually non-operative, often including a change in shoe wear and activity modification. However, patients that have ongoing symptoms once non-surgical treatments are tried, often consider surgery to remove the prominent accessory navicular and, if necessary, reattach the posterior tibial tendon.



Causes
An accessory navicular develops as a result of a congenital anomaly and is found more often in women. If the bone is large, it may rub against a shoe, causing pain. Because of its location, the posterior tibial tendon may pull on the bone during walking or running, causing the fibrous tissue that connects the accessory navicular to the navicular to tear and become inflamed.

Symptoms
Symptoms of accessory navicular syndrome often appear in adolescence, when bones are maturing. Symptoms include A visible bony prominence on the midfoot, Redness and swelling, Vague pain or throbbing in the arch, especially after physical activity.

Diagnosis
Plain x-rays are used to determine the size of the accessory navicular. There are three main types of accessory navicular bones: a small bone embedded within the nearby posterior tibial tendon; a triangular shaped bone connected to the navicular by thick cartilage; and a large prominent navicular tuberosity thought to represent an accessory navicular that has fused to the navicular. If the status of the posterior tibial tendon needs to be assessed or if other problems are suspected, (ex. Navicular stress fracture) it may be necessary to perform an MRI. Although this is not considered routine, an MRI may be helpful in identifying the degree of irritation. An MRI would demonstrate fluid or edema that may accumulate in the bone as a result of the irritation.

Non Surgical Treatment
Many individuals with symptomatic accessory naviculars can be managed successfully without surgery. Standard non-surgical treatment includes shoes that are soft around the inside of the ankle can allow for any excess prominence of bone. Therefore, it is recommended that either shoes with plenty of padding and space in the ankle area are purchased, or pre-owned shoes can be modified by a shoemaker to create extra space in this area. For example, many patients will get their ski boots expanded in the area around the prominence, minimizing irritation. In addition, a shoe with a stiff sole will help disperse force away from the arch of the foot during walking, thereby minimizing the force on the posterior tibial tendon. An off-the-shelf arch support may help decrease the stress applied by the posterior tibial tendon. If necessary, an ankle brace applied to provide more substantial support to the arch may be successful where a simple arch support fails.



Surgical Treatment
Surgical treatment of the accessory navicular syndrome with simple excision has the advantages of less invasive to the posterior tibial tenden and the medial longitudinal arch of the foot, shorter time of immobilization of the foot and stay in hospital, small incision and good clinical results. This procedure is one of the best selective treatments for the accessory navicular syndrome, especially for the patients without flatfoot deformity and old sprain injury.