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.