Only 60 patients will be included in the RSA part of the trial. The precision of the RSA will be evaluated by double investigations at a 1-year follow-up. The patient receives two images separated by a short period of time. The patient is first radiographed, then he/she takes a walk in the investigation room, and is then radiographed again. Micromotion between these two images is not real, so then we know the precision of our method. The limits for significant differences are calculated as 99% confidence intervals of absolute differences for the double investigation. The upper limits for "mean error of rigid body fitting" and "condition number" are set to 0,35mm and 130. These parameters describe the stability of the marker and the spreading, and expresses the precision of the software. At least 20 patients are needed in each group, but the technical demanding procedure has a drop-out risk, leading us to include 30 patients in each group (23).