MODEL RELEASED. Testing artificial hip. Patient being prepared for a scan of her artificial hip by radiostereometric analysis (RSA). RSA involves the use of X-rays to follow the motion of metal markers attached to the prosthesis inside the leg. Two X-rays are taken, one from below and one from the side, to obtain a three-dimensional picture. This is a high-precision technique that can track small motions in the skeleton. This is part of research to study the stability of hip prostheses. Photographed at the Biomechanical Laboratory, Rizzoli Institute, Bologna, Italy.