Disclosed herein is a method ofdefin-ing a mating surface in a first side of an arthroplastyjig. The mating surface is configured to matinglyre-ceive and contact a corresponding patient surfacein-cluding at least one of a bone surface and a cartilagesurface. The first side is oriented towards the patientsurface when the mating surface matingly receives andcontacts the patient surface. The method may include:a) identifying a contour line associated with the patientsurface as represented in a medical image； b)evaluat-ing via an algorithm the adequacy of the contour linefor defining a portion of the mating surface associatedwith the contour line； c) modifying the contour line ifthe contour line is deemed inadequate； and d)employ-ing the modified contour line to define the portion ofthe mating surface associated with the contour line.
