What Is Accessory Navicular Syndrome

Overview
For most people with an accessory navicular, the extra bone does not cause any problems and most are unaware of its presence. But certain activities or circumstances may cause the extra bone or the tibialis posterior tendon that contains it to grow irritated. This is called accessory navicular syndrome, and its possible causes include sprains, overuse, or wearing shoes that constantly rub against the bone. Individuals who have a collapsed arch (commonly known as flat feet) may be at greater risk of accessory navicular syndrome, assuming they have the extra bone, because of the added daily trauma placed on the tibialis posterior tendon.



Causes
Most of the time, this condition is asymptomatic and people may live their whole lives unaware that they even have this extra bone. The main reason the accessory navicular bone becomes problematic is when pain occurs. There is no need for intervention if there is no pain. The accessory navicular bone is easily felt in the medial arch because it forms a bony prominence there. Pain may occur if the accessory bone is overly large causing this bump on the instep to rub against footwear.

Symptoms
Adolescence is a common time for the symptoms to first appear. This is a time when bones are maturing and cartilage is developing into bone. Sometimes, however, the symptoms do not occur until adulthood. The signs and symptoms of accessory navicular syndrome include a visible bony prominence on the midfoot (the inner side of the foot, just above the arch) Redness and swelling of the bony prominence. Vague pain or throbbing in the midfoot and arch, usually occurring during or after periods of activity.

Diagnosis
To diagnose accessory navicular syndrome, medical staff ask about the patient?s activities and symptoms. They will examine the foot for irritation or swelling. Medical staff evaluate the bone structure, muscle, joint motion, and the patient?s gait. X-rays can usually confirm the diagnosis. MRI or other imaging tests may be used to determine any irritation or damage to soft-tissue structures such as tendons or ligaments. Because navicular accessory bone irritation can lead to bunions, heel spurs and plantar fasciitis, it?s important to seek treatment.

Non Surgical Treatment
Excess weight will increase the force on the posterior tibial tendon as it inserts into the accessory navicular and will tend to precipitate or aggravate symptoms. If a patient with a symptomatic accessory navicular is overweight, then losing weight can be very helpful. Even losing 5-10lbs will decrease the amount of force going through the foot with each step by as much as 15-30lbs. This is because the foot acts like a lever serving to magnify the force absorbed by the foot with each step.



Surgical Treatment
If non-operative treatment fails to relieve the patient’s symptoms, surgical intervention may be warranted. The standard operative treatment of an accessory navicular is a Kidner procedure. However, if surgery is undertaken it is important that it address the underlying source of the patients pain.