1. A method of determining a reference point on condyles of a femur using a computer assisted surgery system, the method comprising: providing a digitizer having a trackable member which is locatable and trackable in three dimensional space by the computer assisted surgery system, the digitizer including perpendicular first and second planar surfaces; creating a digitized plane using the digitizer, the digitized plane being at least one of a posterior plane and a distal plane of the condyles, the posterior plane and the distal plane being respectively defined by said first planar surface and said second planar surface of the digitizer; and determining a location of the reference point in the digitized plane using the computer assisted surgical system, the reference point being a most remote point of the femur within said digitized plane.