MODEL RELEASED. Testing artificial knee. Patient being prepared for a scan of her artificial knee 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 X-ray film is seen below the patient's knee and one behind it. This is a high-precision technique that can track small motions in the skeleton. This is part of research to investigate the stability of knee prostheses. Photographed at the Biomechanical Laboratory at the Rizzoli Institute, Bologna, Italy.