Abstract: An augmented reality guidance system for guiding surgical operations on an articulating portion of a bone includes a tracking element to be attached to the articulating portion and-having a surface bearing against the portion that is custom-designed from a virtual model , and a three-dimensional reference mark ; a probe with a three-dimensional reference mark for probing at least three regions of a portion apart from the cartilage area; a camera for displaying and tracking the reference marks ; and a processing system for processing virtual bone model data and real-time image data from the camera to determine the position and relative direction of the tracking element and probe, to display on a display device , a three-dimensional virtual representation of a geometric datum relating to the bone model having position and direction determined by the position and direction of the tracking device and corrected after probing.