Patent ID: 7567834

Claim:
An apparatus to determine a position for implanting a prosthesis in an anatomy, comprising: an instrument including a sensor; a system operable to navigate a procedure, including a tracking system that tracks the sensor to determine a position of the instrument relative to the anatomy, the tracking system spaced apart from the instrument; an imaging device to obtain image data of the anatomy; a display that displays the image data; a user input device that enables a user to select a plurality of points on the image data displayed on the display; wherein said system is configured to determine a first anatomical definition based substantially only on the plurality of points, the first anatomical definition including at least a midline plane of a spinal column; wherein said first anatomical definition is substantially independent of the orientation of the image data; and wherein an icon that represents the prosthesis is displayed on the display relative to the image data, and the icon changes when the prosthesis is on the midline plane.