The accessory navicular--an important cause of medial foot pain.

The accessory navicular is a commonly occurring accessory ossicle of the foot. In most instances this is an incidental finding. In some patients, the accessory navicular is the direct cause of foot pain. We present 10 such cases. The typical clinical picture is of a young female patient who presents with chronic or acute on chronic medial foot pain centered over the medial side of the navicular. The patient is usually physically active on her feet and localizes the pain accurately. Plain radiography reveals an accessory navicular united to the navicular by a synchondrosis (Type II). The diagnosis can be confirmed by showing increased localized uptake of isotope on a technetium 99m MDP bone scan. In some cases, the accessory navicular is mistaken for a fracture. Awareness of this accessory ossicle causing such symptoms should lead to the correct diagnosis.