Fig. 4

Outputs of the three-dimensional (3D) foot scanning system. The positions of the second toe tip (a), heel (midpoint of the width of the calcaneal tuberosity) (b), navicular bone (c), and instep (d) were identified as feature points using the 3D foot scanner. In the present study, five 3D foot skeletal indices were used, including the distance from the heel to the tip of the second toe (foot length [FL: Line a–b]), height of the navicular bone from the floor (navicular height [NH: Line c]), distance from the floor to the highest point of the talus head (instep height [IH: Line d]), second toe–heel–navicular angle (SHN angle: angle made by abc), and the distance from the center line (Line a–b) when the coordinate point of the talus head is projected onto the floor (axis of the bone distance [ABD: Line ab-d]). The derived distance information is influenced by the FL; therefore, normalization was performed with the distance from the heel to the tip of the second toe as a reference (e.g., NH/FL = NH rate)