Fig. 1

Model-based RSA process for tracking stem migration over time. a AP radiograph showing reference markers (yellow) and control markers (green) used for calibration. b Visualization of the tantalum beads (red), inserted during surgery into the cancellous bone as femoral markers. c Implant outline serves as the basis for the 3D surface model of the implant, with its actual projection relative to the markers, used for assessing the implant’s position and rotation by matching the two synchronized radiographic stereo images. d–f Illustrations of a 3D implant model visualizing stem migration from (d) baseline, through (e) 6 weeks, to (f) 6 months post-THA, with the dashed line indicating the level of the stem shoulder at baseline