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 degrees pelvic tilt, average cup inclination was 46.2 degrees (32 degrees to 65 degrees ; +/-7.0 degrees ), and average cup anteversion was 19.8 degrees (4 degrees to 37 degrees ; +/-9.1 degrees ). At neutral pelvic tilt, inclination was 44.5 degrees (28 degrees to 59 degrees ; +/-7.2 degrees ), and anteversion was 15.6 degrees (-5 degrees to 33 degrees ; +/-8.1 degrees ). At -10 degrees pelvic tilt, inclination was 42.6 degrees (25 degrees to 61 degrees ; +/-7.2 degrees ), and anteversion was 10.5 degrees (-10 degrees to 37 degrees ; +/-12.2 degrees ). 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.