Abstract: A computer assisted surgical system for guiding bone cutting operations of an arthroplasty surgery is provided. The computer assisted surgical system includes a cutting guide having a guiding surface for mounting to a bone and a computer. The computer is in communication with the cutting guide and configured to generate a bone model of the first bone without the use of pre-operative bone images, determine a position of an implant model having a bone interface surface on the bone model, determine a position of the cutting guide on the first bone based on the determined position of the implant model on the bone model, and position the guiding surface of the cutting guide to one of a plurality of predetermined cut configurations relative to the bone interface surface.