A simplified roentgen stereophotogrammetric method. Analysis of small movements between the prosthetic stem and the femur after total hip replacement.

A simplified roentgen stereophotogrammetric method is described. It is based on the use of a 50 mm thick reference plate consisting of a carbon-fibre-reinforced polyester box. The patient is placed directly on this box, which makes the methods less cumbersome and more suitable for routine use. The method has been tested in a model experiment designed for detecting small movements between femur and prosthesis at an early stage after total hip replacement. The head and two hemispheres on the prosthesis and three small tantalum balls inserted in the femur serve as reference points. The model experiment now reported shows that the method has acceptable precision.