A tibia cutting assembly includes a tibia cut guide with at least one cutslot. A guide rodhas a guide holder mountable to the cut guide at a first end of the guide rod,and asecond end of the guide rod is mountable non-invasively about a skin of apatient. Theguide rod is extendable in length to displace the tibia cut guide and adjust apositionthereof with respect to a tibia of the patient. The guide holder cooperateswith the tibiacut guide to adjust an orientation of the tibia cut guide. A first inertialsensor ismountable to the guide holder and is displaceable therewith, and a secondinertialsensor is mountable to the guide rod at the second end thereof.
