Introduction

Not everyone has the same number of bones in his feet. It is not uncommon for both the hands and the feet to contain extra small accessory bones, or ossicles, that sometimes cause problems.  

Anatomy

The accessory navicular is a congenital anomaly, meaning you are born with an extra bone in your foot. If there is an accessory navicular, it is located in the instep where the posterior tibial tendon attaches to the real navicular bone.
As the skeleton completely matures, the navicular bone and the accessory navicular bone never completely fuse into one solid bone. The two bones are joined by fibrous tissue or cartilage. Girls seem to be more likely to have an accessory navicular than boys.

Causes

Having an accessory navicular bone is not necessarily a bad thing. Not all people with accessory bones have symptoms. Symptoms arise when the accessory navicular bone is overly large or when an injury disrupts the fibrous tissue between the navicular and the accessory navicular bones. A very large accessory navicular may cause a bump on the instep that rubs on your shoe causing pain.

An injury to the fibrous tissue connecting the two bones can cause something similar to a fracture. The injury is prone to poor healing and may cause continued pain. The pain may result from motion between the navicular and the accessory navicular. The posterior tibial tendon attached to the accessory navicular constantly pulls on the bone creating motion between the fragments with each step.

Symptoms

The primary reason an accessory navicular becomes a problem is pain. There is no need to do anything with an accessory navicular not causing pain. The pain is usually at the instep area and can be pinpointed over the small bump in the instep. Walking can be painful when the problem is aggravated. The problem commonly appears during the teenage years.

Diagnosis

The diagnosis begins with a complete history and physical examination by your surgeon. Usually the condition is suggested by the history and the tenderness over the area of the navicular. X-rays will usually be required to allow the surgeon see the accessory navicular. Generally no other tests are required.

Treatment

The treatment for a symptomatic accessory navicular can be divided into nonsurgical treatment and surgical treatment. In the vast majority of cases, treatment usually begins with nonsurgical, or conservative, measures. Surgery usually is considered when all conservative measures have failed to control your problem and the pain becomes intolerable.

Conservative Treatment

If the foot becomes painful following a twisting type of injury and an X-ray reveals the presence of an accessory navicular bone, your doctor may recommend a period of immobilization in a cast or splint. This will rest the foot and perhaps allow the disruption between the navicular and accessory navicular to heal. If the pain subsides, then no further treatment may be necessary. Sometimes an arch support can relieve the stress on the fragment and decrease the symptoms.

Surgery

If conservative measures fail and the fragment continues to be painful, surgery may be recommended.

The most common procedure used to treat the symptomatic accessory navicular is the Kidner procedure. To perform this procedure, a small incision is made in the instep of the foot over the accessory navicular. The accessory navicular is then detached from the posterior tibial tendon and removed from the foot. The posterior tibial tendon is reattached to the remaining normal navicular. Following the procedure, the skin incision is closed with stitches, and a bandage and splint are applied to the foot and ankle.  

Rehabilitation

Following surgery, you may need to use crutches for several days. A physical therapist or nurse may teach you how to properly use your crutches. Your stitches will be removed in ten to fourteen days (unless they are the absorbable type, which will not need to be removed). You may be released to full activity in about six weeks.