1. A method for determining a position of a joint prosthesis using a computer assisted orthopedic surgery system in support of an arthroplasty surgery of a joint of a patient comprising: attaching a first locatable element to a first bone on one side of the joint; providing a sensor comprising a second locatable element; moving the sensor in proximity of the joint, wherein a plurality of positions on the first bone is located by locating a plurality of positions of the sensor relative to the first locatable element using a tracking device; selecting a generic model of a joint that is not specific to the patient; deforming, with the use of a computer, the generic model in response to the plurality of positions located on the first bone of the joint; determining an initial position of a joint prosthesis on the deformed model; determining a section plane in the deformed model corresponding to the initial position of the joint prosthesis; determining a contour between a surface of the deformed generic model and the section plane; and displaying the contour of the deformed generic model on a display.