Merle C, et al. - Researchers evaluated native acetabular offset (AO) measurements performed on conventional supine anterior-posterior (ap) pelvis radiographs for the accuracy and reliability with reference to computed tomography (CT) in patients with end-stage hip osteoarthritis (OA). In addition, they determined the minimum and maximum amount of medialization of the center of rotation (COR) simulating different reaming techniques and sought for factors indicating an increased risk of excessive medialization of the COR. They evaluated a consecutive series of corresponding 131 CT scans and radiographs of patients with primary hip OA using validated software for three-dimensional acetabular and femoral measurements and identified that patients with primary OA display variability in acetabular anatomy. Conventional radiographs were identified as reliable for accurately determining AO and this was noted irrespective of femoral shape and geometry. A substantial number of patients appeared to be at risk for excessive cup medialization depending on the preferred reaming technique. A mean implant-related medialization of 5.9 ± 3.4 mm was noted with cup placement in the most lateral position (anatomic reaming technique). The total medialization of the COR (implant-related and reaming-related) was 6.8 ± 2.9 with the conventional reaming technique, with 34% of cases having a medialization ≥8 mm.