Roentgen Stereogrammetric Analysis (RSA) is a radiographic method used to measure skeletal and implant movements with very high resolution in vivo. The method involves inserting small tantalum markers in the bone during surgery and taking two simultaneous radiographs over a specialised calibration cage which allows three-dimensional movements to be measured. The use of RSA methodology dates back to the early 1970’s and has first been described in the thesis by Göran Selvik.
The method has continued to be developed over time with digital radiographs and software measurements reducing the time taken for analysis. As a result, RSA is now used in a large number of different applications varying from implant fixation and wear over time, measuring bone growth, fracture stability during healing, osteotomy stability, tendon healing and dynamic movements.