Radiographic analysis
ischium, adduction
POSITIVE
All patients underwent RSA imaging in a supine position at 2, 4, and 6 weeks, 3 and 6 months, and 1 and 2 years postoperatively. A uniplanar calibration cage (RSA Biomedical, Umea, Sweden) was used to define the coordinate system and ensure patients were consistently positioned at each exam. Model-based RSA software (RSAcore, Leiden, The Netherlands) was used to analyse the acquired radiographs. Positive translation directions were defined as proximal translation in the y-axis, medial translation in the x-axis, and anterior translation in the z-axis. Positive rotation directions were defined as internal rotation about the y-axis, anterior rotation about the x-axis, and adduction about the z-axis.To further evaluate acetabular cup position, anteversion and inclination angles were measured from the anteroposterior (AP) and lateral radiographs acquired at the standard 6-week postoperative visit. The anteversion angle was measured on the lateral radiograph using the ischiolateral method, where the ischium was used as an anatomical landmark. The anteversion angle was defined as the angle between a reference line made perpendicular to the long axis of the ischium and a line across the opening of the cup minus 26°.