A system for calculating a position and orientation of an acetabular cup in computer-assistedsurgery comprises a first trackable reference secured to a pelvis, with a frameof reference being associated with the first trackable reference. A device ispositionable between a femoral neck and the acetabulum of the pelvis in a knownrelation, the device having a second trackable reference. Sensors track thetrackable references for position and orientation. A position/orientationcalculator calculates a position and orientation of the frame of reference andof the device and for determining an orientation of the neck axis with respectto the frame of reference from the known relation at a desired position of the femur.An implant position/orientation calculator provides cup implanting informationwith respect to the orientation of said neck axis as a function of the trackingfor position and orientation of at least the first trackable reference.
