Snijders TE, Schlösser TPC, Heckmann ND, et al. - A case-control study was performed to correlate variations in 3-D acetabular cup orientation during functional pelvic tilt between posterior total hip arthroplasty (THA)A dislocations versus stable THAs. Researchers compared standing and sitting 3-D cup orientation between fifteen posterior dislocations versus 233 prospectively followed stable THAs. Using previously validated trigonometric algorithms on biplanar radiographs, 3-D cup orientation was estimated. There is a lower increase of all three orientation angles from standing to sitting comparing posterior THA dislocations to stable THAs. As per the findings, this leads to a reduced sitting coronal inclination and sagittal ante-inclination which may lead to an elevated risk of impingement ensued by THA instability. In both positions, the transverse version was not significantly different. This validates the usefulness of biplanar data on functional cup orientation.