A tibia cutting assembly includes a tibia cut guide with at least one cut slot. A guide rod has a guide holder mountable to the cut guide at a first end of the guide rod, and a second end of the guide rod is mountable non-invasively about a skin of a patient. The guide rod is extendable in length to displace the tibia cut guide and adjust a position thereof with respect to a tibia of the patient. The guide holder cooperates with the tibia cut guide to adjust an orientation of the tibia cut guide. A first inertial sensor is mountable to the guide holder and is displaceable therewith, and a second inertial sensor is mountable to the guide rod at the second end thereof.
