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.
