Measurement of pelvic tilting angle during total hip arthroplasty using a computer navigation system

Abstract

The purpose of this study was to measure pelvic orientation during total hip arthroplasty (THA) in a lateral decubitus position using a computer navigation system with an optical localizer (OPTOTRAK). THA was performed in 17 hips. Much attention was paid to set the patients in neutral axial rotation with the anatomical plane of the pelvis perpendicular to the operating table. After shape-based registration, pelvic orientation was tracked with light emitting diode markers fixed to the pelvis. Measurements were based on the anatomical plane. Mean movement of the pelvis from the supine position to the dislocated lateral decubitus position was 8 degrees posterior (26 posterior to 6 anterior), 3 degrees abducted (6 adduction to 20 abduction), and 4 degrees internally rotated (24 internal to 5 external). This study showed that the pelvis was not always placed in neutral axial rotation, despite the surgical plan. It was further tilted posteriorly and rotated internally when the socket was inserted. This tilt can lead to decreased socket anteversion with conventional alignment guide systems, while unknown pelvic orientation in general can cause socket malposition with such systems. Therefore, intraoperative three-dimensional measurements of pelvic orientation seems to be useful to avoid socket malposition.