The accessory navicular is an extra bone found in under 14% of humans. It is known by several other names, and can potentially be a source of pain and discomfort when walking.
This extra bone is found on the side of the foot facing the other foot, a couple of inches in front of the ankle bone on the side of the foot. It can appear in early childhood, and can become painful in either childhood or early adulthood. The bone is especially aggravated by tight fitting shoes rubbing against it, as well as unsupported foot collapse seen in flat feet, in which the tendon the extra bone rubs against becomes strained. Twisting injuries can also irritate this bone as well.
Symptoms can vary, but typically involve a specific point of pain directly on the bone. If it is prominent enough, the skin overlying the bone will become red, and a protective bursal sac may form over this site and subsequently become inflamed. The bone itself can appear in several different forms, and this can vary the location of and severity of the symptoms. Sometimes the bone is found directly inside the important posterior tibial tendon that attaches to the foot at this spot. Other times, the accessory navicular is located underneath the tendon, attaching to the navicular bone through a fibrous attachment. Finally, the accessory navicular may also form as a direct bony attachment to the navicular, making the side of the navicular look enlarged. In this scenario, the extra bone is very prominent and tender to direct touch, as opposed to when it forms in the tendon, in which most of the pain is felt in the tendon as it is being strained as one's foot flattens.
Treatment of a painful accessory navicular can occur at many levels. Treatment starts off with anti-inflammatory medication and icing to control inflammation, and is followed by arch support through orthotics. Physical therapy can also be used as well. Tight shoes should be avoided, and athletic activity may need to be temporarily decreased to allow for healing. When these measures fail, surgery may be needed to remove the accessory bone from the body. Depending on the severity of the disease, the posterior tibial tendon may also need to be repaired and/or moved slightly under the foot to improve its pull. This procedure generally has a good prognosis, and usually heals well within a month.