Tool and method for digital acquisition of a tibial mechanical axis

A method for determining a mechanical axis of a tibia using an inertial-based computer assisted surgery system and a tibial digitizer having an upper mounting end, a lower mounting end and an alignment rod extending therebetween, the tibial digitizer including at least one inertial sensor in communication with the computer assisted surgery system, the method comprising:

• determining an upper reference point on a tibial plateau of the tibia, the upper reference point being an entry point of the mechanical axis;
• fastening the upper mounting end of the tibial digitizer to the tibial plateau at the upper reference point;
• fastening the lower mounting end of the tibial digitizer to medial and lateral malleoli of the ankle;
• determining a lower reference point located at a midpoint between the medial and lateral malleoli by identifying a corresponding midpoint on the lower mounting end of the tibial digitizer;
• adjusting an orientation of the alignment rod such that the alignment rod is aligned with an anatomical landmark on the tibia;
• and
• using the computer assisted surgery system to determine the mechanical axis of the tibia extending between the upper and lower reference points by providing at least orientation data of the tibial digitizer to the computer assisted surgery system using the inertial sensor.

A digitizing tool adapted for acquiring a mechanical axis of a tibia using a computer assisted surgery system, the digitizing tool comprising:

• spaced apart upper and lower mounting ends each having at least one mounting point respectively adapted to be secured to a tibial plateau and malleoli of the tibia, the mounting point of the upper mounting end being fasteneable to the tibial plateau at a mechanical axis entry point defining an upper reference point;
• an alignment rod extending between and interconnecting the upper and lower mounting ends, the alignment rod defining a longitudinal axis and being disposed a common distance from the mounting points on the upper and lower mounting ends, at least one trackable member mounted to the alignment rod, the trackable member producing at least orientation-based data for at least two degrees of freedom in orientation of the trackable member and thus of the alignment rod;
• the lower mounting end including a self-centering malleoli engagement mechanism having a base portion pivotally connected to the alignment rod and opposed caliper arms slideably mounted on the base portion for displacement relative to each other in a plane transverse to the longitudinal axis of the alignment rod, wherein the caliper arms, when displaced towards each other, are adapted to abut the most medial and lateral points on the malleoli to clamp the self-centering malleoli engagement mechanism in place thereto;
• and
• wherein a midpoint between the caliper arms of the self-centering malleoli engagement mechanism corresponds to a lower reference point located at a midpoint between the most medial and lateral points on the malleoli, and the mechanical axis extends between the lower reference point and the upper reference point at said common distance from the alignment rod which is aligned parallel thereto.