A system for intra-operatively registering a pelvis comprising an acetabulum with a computer model of the pelvis in a coordinate system. The system may include: a) a surgical navigation system including a tracking device； and b) at least one computing device in communication with the surgical navigation system. The at least one computing device: i) receiving first data points from first intra-operatively collected points on an articular surface of the acetabulum, the first data points collected with the tracking device； ii) receiving a second data point from a second intra-operatively collected point on the pelvis, the second data point collected with the tracking device, the second data point corresponding in location to a second virtual data point on the computer model； and iii) determining an intra-operative center of rotation of the femur relative to the pelvis from the first data points.
