1. A method for indicating accuracy of image segmentation in a patient model, the method comprising: creating a three-dimensional bone surface model of a portion of a patient's bone from imaging data; calculating a first signal intensity gradient between a first point on a surface of the three-dimensional model and a second point spaced from the surface along a line extending from the surface at the first point; and marking the first point on the three-dimensional model if the first gradient exceeds a first threshold.