The Os Navicularis (na-vic-u-lar-ris) or accessory navicular (na-vic-u-lar) is an accessory bone (not present all the time) which is present in approximately five to ten percent of the population. The accessory navicular often does not cause any problems but can become painful following increasing activity levels or an injury to the foot. The accessory navicular is present on the inside of foot around the middle of the arch area. The pain occurs due to motion between the accessory bone and the main bone (the navicular). The tendon that is meant to insert into the main bone instead inserts into the accessory bone and creates friction between the two bones which leads to pain.
Management of this condition can include immobilisation, insoles and surgery to remove the accessory bone with reattachment of the tendon onto the navicular.