The risk of dislocation after THA reportedly is minimized if the acetabular implant is oriented at 45° inclination and 15°
anteversion with respect to the anterior pelvic plane. This reference plane now is used in computer-assisted protocols. However,
this static approach may lead to postoperative instability because the dynamic variations of the pelvis influence effective
cup orientation and are not taken into account in this approach. We propose an ultrasound tool to register the preoperative
dynamics of the pelvis for THA planning during computer-assisted surgery. To assess this pelvic behavior and its consequences
on implant orientation, we tested a new 2.5-dimensional ultrasound-based approach. The pelvic flexion was registered in sitting,
standing, and supine positions in 20 subjects. The mean values were −25.2° ± 5.8° (standard deviation), 2.4° ± 5.1°, and 6.8° ± 3.5°,
respectively. The mean functional anteversion varied by 26° and the mean functional inclination by 12° depending on the pelvic
flexion. We therefore recommend including dynamic pelvic behavior to minimize dislocation risk. The notion of a safe zone
should be revisited and extended to include changes with activity.
One or more of the authors (GD) have received funding from the French National Agency of Research, Réseau National des Technologies
pour la Santé.
Each author certifies that his or her institution has approved the human protocol for this investigation and that all investigations
were conducted in conformity with ethical principles of research, and that informed consent for participation in the study
was obtained.