Classification of accessory navicular. Type I, small oval-to-round ossicle within the posterior tibial tendon; no bony or cartilaginous attachment to the navicular. Type II, larger lateral projection from the medial aspect of the navicular; fibrocartilaginous plate less than 2 mm wide and with an irregular outline separates tuberosity from body of the navicular. Type III, “horn”-shaped prominence connected to the navicular by a bony bridge.