Measurement of 3D Distance between Artificial Cement-Type Cup and Head After THR

The purpose of our study is a measurement of 3D (three dimensional) distance between an artificial cement-type cup and a artificial femoral head in a living patient's body after THR(total hip replacement) from an AP(anterior-posterior) Roentgen image and a lateral image, when the angle between the two images is unknown. Recently we proposed a measurement method for non-cement-type cup. We modified the 3D measurement method for a non-cement cup with evolutionary computation(EC) and extend the framework for a cement-type cup. Our method needs only two times of shots using an ordinary Roentgen equipment without measurement the angle of the two images. So our method is superior to Martell's Method. And it needs no metal balls in a patient body unlike RSA (Roentgen stereophotogrammetric analysis). We show the result of a computer simulation with CG (computer graphics) image we made and the result in vitro with Roentgen images of artificial cup and head moved by a micro-manipulator.