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.
[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.
Because of this, RSA is an important technique in early clinical trials for screening new joint replacement prostheses.
To achieve the high accuracy, the following steps are carried out: Small radio opaque markers are introduced in the bone and attached to the prosthesis to serve as well-defined artificial landmarks.
The reported accuracy of RSA ranges between 0.05 and 0.5 mm for translations and between 0.15˚ and 1.15˚ for rotations (95% confidence interval).