Radiostereometric analysis
The first RSA recording was performed within 24 h after surgery and after the patient had been weight-bearing. A standard RSA system with 2 synchronized ceiling fixed roentgen tubes angled 40° towards each other and a uniplanar calibration box (Carbon Box 19, RSAcore, Leiden, The Netherlands) was used [RSA analysis was done marker-based with an EGS cylinder model referenced to the lag screw to align the coordinate system in the screw y-axis (yellow). The x-axis (red) was aligned with the horizontal image plane and the z-axis (green was directed out of plane. The screw markers (red), the head/neck markers (pink), and trochanter markers (blue) were combined in marker-models for each model. The direction of the displayed axes (x, y and z) corresponds to positive values