“…Investigators have shown the importance of hip-spine relations and how differences in pelvic tilt in different positions can affect the risk of THA impingement [ 1 , 3 , 6 , 16 , [20] , [21] , [22] ]. Computer simulations and preoperative planning software have been developed to optimize the orientation of acetabular implants by considering sagittal pelvic tilt [ [23] , [24] , [25] , [26] , [27] , [28] , [29] ]. Many of these software programs concentrate on pelvic tilt in standing and relaxed sitting positions, but sagittal pelvic tilt in flexed seated positions is not always considered.…”