The accessory navicular synchondrosis.

The accessory navicular, which is considered an anatomic variant, may be the source of pain in athletes. There are three types of accessory naviculars: Type I is an ossicle in the substance of the posterior tibial tendon; Type II forms a synchondrosis with the navicular; and Type III, "the cornuate navicular," represents the possible end stage of Type II. Nine feet had Type II accessory naviculars. The pull of the posterior tibial tendon, the degree of foot pronation, and the location of the accessory navicular in relation to the undersurface of the navicular are factors that produce tension, shear, and/or compression forces on the synchondrosis of Type II accessory naviculars and cause microscopic changes of injury and repair similar to those observed with a physeal fracture. Such alterations are not always visible on roentgenograms but are usually detected by 99mTc methylene diphosphonate (99mTcMDP) scans. Initially, nonsurgical treatment with orthotics or casts should be attempted, but if this is unsuccessful, surgical treatment is recommended. Surgical treatment consists of excision of the accessory navicular with its synchondrosis, without transposition of the posterior tibial tendon.