A method of generating a customized patient-specific negative contour of a customized patient-specific bone cutting block involves determining a cartilage thickness value, determining a reference contour corresponding to a surface contour of a three-dimensional model of the relevant end of the patient's bone, determining a reference point in the three-dimensional model of the patient's bone, increasing the distance between the reference point and a point on the reference contour, and defining a customized patient-specific negative contour of the customized patient-specific bone cutting block using the scaled reference contour.