Provided is a guide assembly for guiding a bone cutting tool through a small incision in the skin near the bone that allows movement of the cutting tool in the bone in a wide angle while the cutting tool is rotated about a pivot point that is located at the small incision. The guide assembly includes a 2-piece construction that includes a guide component that holds the cutting tool and a track component having a semicircular arc shape on which the guide component is slidably engaged whereby sliding the guide component along the track component guides the movement of the cutting tool to rotate about a pivot point that is the center of curvature of the semicircular arc shape of the track component.