Fig. 4

Radiographic measurements of ankle and subtalar joint alignment parameters on whole-leg anteroposterior weight-bearing radiographs. Line (a) represents the mechanical axis of the tibia, (b) the subchondral plate of the distal tibial articular surface, (c) a tangent to the talar dome, (d) a horizontal reference line parallel to the ground, (e) a line perpendicular to the ground, and (f) a line extending from the lowest point of the calcaneus to the center of the talar dome. The tibiotalar tilt angle (TTA) is defined as the angle between lines (b) and (c), the tibial plafond inclination angle (TPIA) is the angle between lines (b) and (e), the talar inclination angle (TIA) is the angle between lines (c) and (e), and the hindfoot alignment angle (HAA) is the angle between lines (a) and (f)