Ball-and-socket ankle joint: anatomical and kinematic analysis of the hindfoot.

Ten feet in eight children with ball-and-socket ankle joint (BSA-J) are reported with discussion of associated anomalies, kinematic analysis of the hindfoot motion, and talocalcaneal malalignment in the apparent valgus deformities. BSA-J is considered to be a common congenital condition associated with other anomalies in the foot or lower extremities. Even though BSA-J seems to have unusual side-to-side motion at the ankle joint, it does not occur in patients without subtalar fusion. Moreover, apparently valgus feet are responsible for talocalcaneal malalignment, not for lateral unstable motion at the ankle.