Methods and apparatus using a surgical navigation system to position the femoral component of a prosthetic hip during hip joint replacement surgery without separately affixing a marker to the femur. The navigation system acquires the center of rotation of the hip joint as well as at least one point on the femur in the pelvic frame of reference. From these two points, the navigation system calculates the position and length of a first line between the center of rotation of the hip joint and the point on the femur. Optionally, a second point on the femur that is not on the first line is palpated. The system can calculate the position and length of a second line that is perpendicular to the first line and that runs from the first line to the second palpated point on the femur. The prosthetic cup is implanted and its center of rotation is recorded. A tool for forming the bore within which the stem of the femoral implant component will be placed is tracked by the navigation system. While the tool is fixed to the femur, the surgeon re-palpates the same point(s) on the femur that were previously palpated. The navigation system calculates the position and length of a first line between the center of rotation of the prosthetic cup and the re-palpated first point. If a second point on the femur was re-palpated, the navigation system also calculates the position and length of a perpendicular line between the first line and the second point. The surgical navigation system uses this information to calculate and display to the surgeon relevant information about the surgery, such as change in the patients leg length and/or medialization/lateralization of the joint.Linvention concerne des procédés et appareil utilisant un système de navigation chirurgical pour positionner le composant fémoral dune prothèse de hanche pendant une chirurgie de remplacement darticulation de la hanche sans poser séparément de marqueur sur le fémur. Le système de navigation acquiert le centre de rotation
