In Vitro Investigation of the Influence of Pelvic Tilt on Acetabular Cup Alignment

This study investigates the influence of pelvic tilt on conventional alignment of acetabular cups. Cementless cups were aligned into a synthetic replica of the pelvis 300 times at different pelvic tilts. At +10° pelvic tilt, average cup inclination was 46.2° (32° to 65°; ±7.0°), and average cup anteversion was 19.8° (4° to 37°; ±9.1°). At neutral pelvic tilt, inclination was 44.5° (28° to 59°; ±7.2°), and anteversion was 15.6° (−5° to 33°; ±8.1°). At −10° pelvic tilt, inclination was 42.6° (25° to 61°; ±7.2°), and anteversion was 10.5° (−10° to 37°; ±12.2°). Overall, 50% of the cups were positioned outside the safe zone: 46% in pelvic inclination, 42% in neutral position, and 63% in pelvic reclination (P = .007). This study shows the considerable inaccuracies of conventional cup implantation by experienced and trainee surgeons and shows the influence of pelvic tilt on acetabular cup alignment.