Fig. 1

Definition of the tibia ARS: a) cylinder fitted on the tibial plafond and the z axis; b) origin; c) x axis definition; d) final ARS. In this and following figures a left foot is considered; the portion of articular surfaces used for the fitting of geometrical feature is represented in red; the construction curves are in green; the final x, y, and z axes of the ARS are in blue, represented by one, two and three arrows respectively