Digital tool for obtaining a tibial mechanical axis

A tool (10, 210) for digitizing an axis (Z) mechanic.ZCOO tibia (T) using a surgical system computer aided tool comprises: one end (12) of upper assembly and one end (14) mounting lower interconnected by a rod (18, 218) extending alignment between them, with the mounting end releasably attachable upper to a point (P2) upper reference on a plateau (9) tibial; at least one element (54) mounted trackable alignment rod of the tool, the trackable member being adapted to communicate with a computer system computer assisted surgery to provide at least the same orientation information; wherein the end of lower assembly has a mechanism (16) coupling autocentrante malleoli, the coupling mechanism Concentric malleoli including arms (24, 224) of opposite tongs each having a clamp (28, 228) malleolus can moving the gripper arms in a common plane with each other for clamping engagement with medial and lateral malleoli so that a midpoint between the arms of the clamp is an axis passing through a midpoint of the mechanism autocentric and a point (P1) lower reference defined midway between the medial and lateral malleoli; wherein the alignment rod is aligned parallel with the mechanical axis of the tibia which extends between the upper reference point and the lower reference point when the tool is mounted on the tibia.