Measurement of 3D Distance between Artificial Cup and Head from AP & Lateral Roentgens with Unknown Angle after THR

The purpose of our work is measurement of 3D distance between a cup as an artificial acetabular and a head as an artificial femoral head in a patient body from AP and lateral Roentgen images without known angle between AP (anteriorposterior) and lateral after THR (total hip replacement). Martell measured the 2D distance between a cup and a head of an artificial hip joint. And also RSA (Roentgen stereophotogrammetric analysis) is famous as a 3D measurement method of things in a living body. But RSA needs expensive equipments. Our method needs only an ordinary Roentgen equipment and doesn't need to know the angle between AP and lateral. But our method is applied only to the cases of cups which rotation is identified with such as a notch. We show the result of a computer simulation with CG image we made and the result in vitro with real Roentgen images of artificial cup and head moved by a micromanipulator.