A method of determining surgical parameters in computer-assisted surgery system is provided. The surgical parameters are for guiding an operator in inserting a hip joint implant in a femur. The method comprises the steps of: i) digitizing a frame of reference of the pelvis, the frame of reference of the pelvis being trackable in space for position and orientation； ii) digitizing a first frame of reference of the femur as a function of the frame of reference of the pelvis； iii) obtaining a reference orientation for the frame of reference of the femur with respect to the frame of reference of the pelvis； iv) digitizing a second frame of reference of the femur with respect to said reference orientation as a function of the frame of reference of the pelvis, after initiation of implant reduction； whereby surgical parameters associating the femur to the pelvis are determined as a difference between the first and second frames of reference of the femur.
