High Variability in Functional Pelvic Tilt in Patients Undergoing Total Hip Arthroplasty

Abstract

Introduction/objectives: The sagittal rotation of the pelvis changes during daily activities, which potentially influences the functional anteversion and inclination of the acetabular cup in patients having total hip arthroplasty (THA). The aim of this study was to quantify changes in pelvic tilt between different functional positions. Methods: Lateral full body x-ray images of THA patients were taken with EOS imaging system in the standard low-dose protocol. Pelvic tilts were measured using Centricity Enterprise Web 4.0 2010 GE Healthcare IT at three functional positions - standing, seated and flexed seated (the rising action initiated when leaving from the seated position) by two independent observers. Anterior pelvic tilt was assigned a positive value. Results: Pelvic tilts of 27 patients were measured (mean age: 61-years-old, ranged 30-83; sex: M:F = 13:14 ). The mean pelvic tilts were 5.02° (-27.80° to 21.90°), -18.73° (-48.10° to 24.40°) and -5.07° (-49.80° to 38.20°) at the three functional positions, respectively. The mean sagittal pelvic rotation from standing to seated was -10° (-46.70° to -10°), from standing to flexed seated was -4.44° (-48.4° to 18.90°) and from seated to flexed seated was 6.12° (-33.60° to 26.80°). In 16 patients (59%), the extent of sagittal pelvic rotation could lead to functional malorientation of the acetabular component. Conclusion: High variability of the sagittal pelvic rotation was observed. The intraoperative positions of acetabular components based on local pelvic anatomy alone may fail to predict clinically significant changes in its orientation when patients resume functional activities. The optimal acetabular component position is patient-specific, and preoperative functional pelvic tilt should be taken into consideration.