Accessory Navicular Syndrome

(tendonitis and tendosynovitis)

An accessory navicular is an extra bone adjacent and proximal to the tuberosity of the navicular in the inner arch of the foot. At a minimum, the accessory navicular bone is present in 14% of the population. Of those with the accessory navicular bone, 50% of these patients have accessory navicular bones in both feet. Usually the accessory bone is asymptomatic, but can be associated with pain and discomfort due to injury, trauma, or irritation of the posterior tibial tendon near its insertion to the tuberosity of the navicular.    

There are 3 types of accessory navicular syndrome. Each type can be viewed as the degree of fusion of the accessory navicular bone with the tuberosity of the navicular. The types are:

• Type I: An accessory navicular or os tibiale externum within the posterior tibial tendon not attached to the navicular. Type I is generally asymptomatic.
• Type II: Synchondrosis or forming of a tight joint with the navicular. Possible insertion of the posterior tibial tendon into the accessory navicular. This is the most common type.
• Type III: Fusion of the accessory navicular or ossicle with the navicular to form a hooked tuberosity of the navicular.

Symptoms:

• Pain local to the medial foot and posterior tibialis
• Signs of pain beginning as a young adolescent due to the ossification of cartilage
• Increased pain due to weight bearing, physical activity or narrow shoes
• Bony prominence in the inferior and medial aspect of the foot
• Signs of irritation near the aforementioned bony prominence  

Diagnosis:

Diagnosing a patient with accessory navicular syndrome includes asking the patient about symptoms and performing a physical examination of the inferior, medial midfoot. Doctors are likely to examine for a bony prominence and irritation of said bony prominence. X-rays are typical to confirm a diagnosis of accessory navicular syndrome and the type accessory navicular syndrome or degree of fusion.

Treatment:

Conservative, non-surgical treatment is the norm. Icing the area of pain can reduce swelling and irritation. Physical therapy, physical activity modifications and orthotics is common treatment for healing and symptom management. Surgical operations can be performed as a last resort treatment to remove the accessory bone and restructure local tissue as needed.

Sources:
https://www.foothealthfacts.org/conditions/accessory-navicular-syndrome-(1)
https://orthoinfo.aaos.org/en/diseases--conditions/ortho-pinion-accessory-navicular/ 
https://posna.org/Physician-Education/Study-Guide/Accessory-Navicular