Disclosed herein is a method of defining a mating surface in a first side of an arthroplasty jig. The mating surface is configured to matingly receive and contact a corresponding patient surface including at least one of a bone surface and a cartilage surface. The first side is oriented towards the patient surface when the mating surface matingly receives and contacts the patient surface. The method may include: a) identifying a contour line associated with the patient surface as represented in a medical image; b) evaluating via an algorithm the adequacy of the contour line for defining a portion of the mating surface associated with the contour line; c) modifying the contour line if the contour line is deemed inadequate; and d) employing the modified contour line to define the portion of the mating surface associated with the contour line.