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 the steps of: 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; locating a plurality of positions of the sensor relative to the first locatable element using a tracking device, the plurality of positions being patient specific data; selecting a generic model of a joint that is not specific to the patient; determining, with the use of a computer, the generic model in response to the plurality of positions located using the tracking device to generate a deformed model; determining a position for a joint prosthesis on the deformed model; and outputting on a display the determined position upon the deformed model, the display being connected to the computer.