A computer-assisted orthopaedic surgery system includes a device for generating a three dimensional geometrical surface model of a first bone and a database containing three 3 dimensional implant models of a plurality of available implants. The system includes a computer that is configured to permit a user to select from the database a first implant and display on a screen the three dimensional implant model of the first implant. The computer superimposes on the screen the implant model on top of the model of the first bone such that the two models are visually identifiable from one another.
