1. A combination of a non-transitory computer readable medium storing machine readable instructions for fabricating a patient specific instrument (PSI) for use as a surgical guide for a surgical implant and of a model of the PSI in a digital format for use in fabricating the PSI, and the PSI, the combination comprising: the machine readable instructions comprising: a region modeling component configured to provide a three-dimensional model of a region of interest within a body from at least one imaging scan of the region of interest, a surgical planning component configured to display a visible portion of a model of the implant and the three-dimensional model of the region of interest to a first user and allow the first user to select a preoperative surgical plan including a position of the implant within the three-dimensional model of the region of interest in a desired orientation, the implant having at least one hidden attribute that is not visible to the first user, the at least one hidden attribute of the implant being an implant extension configured to extend into a bone in the region of interest for maintaining the implant in the desired orientation relative to the region of interest, and a PSI design component configured to prohibit alterations to the preoperative surgical plan selected by the first user, the PSI design component configured to display the at least one hidden attribute that is not visible to the first user, to generate at least one guide structure as extending from the implant extension and out of bone in the region of interest when the implant is in the desired orientation, the PSI design component configured to generate a model of the PSI incorporating at least one guide hole, the PSI design component configured to generate the at least one guide hole by subtracting the at least one guide structure from a generic PSI model, the PSI design component configured to display the at least one guide structure relative to the region of interest while excluding the visible portion of the implant; the model of the PSI in a digital format for use in fabricating the PSI; and the PSI fabricated from the model of the PSI in the digital format to implement the preoperative surgical plan, the PSI fabricated using data related to the model of the PSI in the digital format to control a manufacturing apparatus.