MODEL RELEASED. Testing artificial knee. Patient being prepared for a test of her artificial knee. The motion of the joint over the shin bone (tibia) will be monitored using radiostereometric analysis (RSA). RSA involves the use of X-rays to follow the motion of metal markers attached inside the leg to the prosthesis. Two X-rays are taken. One ray film is in front of the patient's knee and one is beside it, allowing the construction of three- dimensional images. This high-precision technique can track microscopic joint motions. Photographed at the Biomechanical Laboratory of the Rizzoli Institute, Bologna, Italy.