Fig. 2

A global X–Y–Z coordinate system used to describe the motion of the first metatarsal-cuneiform joint. The Y-axis was parallel to the connecting line between the center of the heel and the second toe and pointed back; the X-axis was set perpendicular to the Y-axis and directed from the lateral aspect to the medial aspect of the foot; and the Z-axis was set perpendicular to the XY plane and pointed dorsally. According to the right-hand rule, plantar-flexion, pronation, and internal rotation were defined as positive, and dorsiflexion, supination, and external rotation were defined as negative. pf plantar flexion, df dorsiflexion, pro pronation, sup supination, ir internal rotation, er external rotation