1. A computer-aided design method for producing an implant for a patient prior to operation, the method comprising: generating digital image data with a non-invasive three-dimensional (3D) volume scan of an anatomical region of the patient comprising a defect site that is to receive the implant; generating a polygonal-mesh 3D surface image representing the anatomical region of the patient based on the digital image data; defining a defect margin crestline describing the external boundary of the patient's defect based on a curvature estimation on the polygonal-mesh 3D surface image; generating a digital template of desired anatomy associated with the anatomical region; performing a two-pass thin plate spline (TPS) warp on the digital template to register the digital template specifically to the patient; generating a prototype implant surface based on the defect margin crestline and the registered template of the anatomical region, the prototype implant surface defining an outer surface of a 3D digital model of the implant; generating at least one internal surface and at least one connecting surface with respect to the prototype implant surface to generate the 3D digital model of the implant; and fabricating the implant based on the 3D digital model of the implant.