Certain congenital anomalies involving the bones of the foot produce flattening of the medial longitudinal arch and eversion of the forefoot (planovalgus). These anomalies include vertical talus, accessory tarsonavicular, and fusion of one or more of the tarsal bones (tarsal coalition).

Accessory tarsonavicular is a normal anatomic variant. A secondary center of ossification forms in the medial portion of the tarsonavicular at the attachment of the posterior tibialis tendon. This ossification becomes more prominent and symptomatic during adolescence, either from its size or from repetitive sprains of the fibrous attachment of the ossicle to the navicular. Tarsal conditions are not usually detected until late childhood or adolescence, when they produce pain with walking and inability to invert the foot. Two types of tarsal coalitions have been identified: (1) calcaneonavicular coalition, which involves the calcaneus and the navicular bones; and (2) talocalcaneal coalition, in which the calcaneus is coalesced to the talus.