The bones of the foot occasionally develop abnormally in a child and an extra bone called an accessory navicular is present towards the inside of the foot, in front of the ankle. This bone is present in approximately 10% of the general population but not large enough to cause symptoms in the majority of these individuals.
The extra bone lump present in childhood can be quite uncomfortable because it rubs on shoes. In addition, the feet associated with the accessory navicular are invariably flat. If the child is active and involved in various athletic activities, this will aggravate the inflammation of the tendon that attaches to the accessory navicular.
This tendon is called the posterior tibial tendon and is responsible for maintaining the strength of the arch of the foot. The flat-footedness associated with the accessory navicular usually brings the child for treatment.
Symptoms of accessory navicular include:
• Bone lump on the inside of the foot
• Redness and swelling
A foot and ankle surgeon can diagnose accessory navicular syndrome by conducting a physical exam. X-rays and MRIs may be taken to access the condition and confirm the diagnosis of accessory navicular.
Treatment of the accessory navicular begins with rest, which may include activity modification or temporary immobilization in a boot or a brace. Once the inflammation subsides the foot needs to be supported. The support consists of a specially designed orthotic arch support.
Occasionally, the orthotic will dig into the edge of the accessory navicular bone under the arch of the foot. This is very uncomfortable. For this reason the orthotic support needs to be carefully made. The orthotic support will help control (but not cure) the flat foot and will often decrease the inflammation on the navicular.
Once the navicular inflammation has lessened it is not necessary to perform surgery unless the foot becomes progressively flatter or continues to be painful. For these children, surgery can completely correct the problem by removing the accessory navicular bone and tightening up the posterior tibial tendon that attaches to the navicular bone.