What is an accessory navicular?

An accessory navicular is an extra bone or piece of cartilage in the arch of the foot that may or may not cause problems. It is also referred to as an os navicularum or os tibiale externum. It is incorporated within the tendon of the posterior tibial muscle which attaches in the area. The extra bone is on the medial site of the navicular bone which is the bone that is at the top of the arch of the foot. It occurs in anywhere from 5-15% of the population. It is not always a problem, but the prominence of the bone may make pressure from the footwear painful. Sometime the bone is in such a position that it does affect the angle of pull of the posterior tibial muscle which in turn affects foot function and may cause any number of biomechanical problems, such as a flat foot.

The diagnosis is usually by x-ray where the presence of the bone is obvious. There are several types that the x-ray can help establish which one it is. The Geist classification divides the accessory navicular bones into three different types. Each of the three types affects the structure and function of the foot in different ways and each of the three different types needs a different treatment approach.

The goal treatment is to relieve the symptoms and stop it being painful. If the pain is particularly bad, then placing the foot in a cast or removable walking boot will allow the affected area to rest and help the pain. Ice can also be used to reduce swelling. Oral nonsteroidal anti-inflammatory drugs (NSAIDs) may be used in combination with immobilization to further reduce the pain and inflammation. Exercises and treatments to strengthen the muscles may also be advised, especially over the long term to help prevent a recurrence of the symptoms. Foot orthotic devices are also very useful to protect the area and be especially useful if the accessory navicular is causing a flat foot.

The accessory navicular can be a particular problem is sports such as skiing and ice skating. This is because the footwear in these sports goes right around the foot and its quite rigid. So, if anyone has a prominent piece of bone on the foot, such as an accessory navicular, this can be quite painful and also difficult to treat. Things like donut type padding to get the pressure from the footwear off the area is often helpful. This is also where the skills of a boot maker or a qualified ski boot fitter is invaluable. They are used to dealing with these sorts of problems and can modify the footwear around the prominent bone to make it more comfortable. A podiatrist can often help with all of this.

If the conservative nonsurgical treatments do not relieve the symptoms, then surgery may be appropriate. Surgery might involve removing the extra bone, reshaping the area and repairing the tendon to improve its function. This extra bone is not needed for normal foot function, so theoretically will not be missed.

Craig Payne is a University lecturer, runner, cynic, researcher, skeptic, forum admin, woo basher, clinician, rabble-rouser, blogger and a dad.