Radiostereometric Analysis (RSA) Mechanical loosening of the prosthesis may be suspected if the prosthesis migrates relative to underlying and adjacent bone. Therefore, there is now a consensus that the introduction of new prostheses and new operational methods of prosthesis insertion should be evaluated through migration studies before they can be recommended for use in general. Clinical studies have shown a high predictive power between early migration of joint prostheses and later prosthesis loosening and premature revision. Radiostereometric analysis (RSA) is a very accurate method for assessment of cup migration at precision levels 0.11 mm precision or better.