Roentgen_stereophotogrammetry
Roentgen stereophotogrammetry (RSA) is a highly accurate technique for the assessment of three-dimensional migration and micromotion of a joint replacement prosthesis relative to the bone it is attached to. It was introduced in 1974 by Göran Selvik.[1]
Several studies have found implant migration to be predictive of long-term implant survival and, for most devices, measurement over 2 years might therefore provide a surrogate outcome measure with relatively low numbers of subjects, e.g. from 15 to 25 patients in each group in randomized studies.[2][3][4][5] A smaller number of subjects can be used in these studies as a consequence of the high accuracy of the measurement technique. Because of this, RSA is an important technique in early clinical trials for screening new joint replacement prostheses.