Correcting for Pelvic Posture Influence on Cup Anteversion Measurements

INTRODUCTION Malposition of the acetabular component is a risk factor for postoperative dislocation after total hip arthroplasty (THA)[1]. Current radiographic techniques for assessing cup anteversion have been developed, but they have limitations[2]. The purpose of this study is to investigate the effect of and reduce the error caused by various pelvis postures on cup anteversion measurement. We hypothesize measurement of cup anteversion has a strong linear relationship with pelvis tilt or rotation. Applying techniques that measure pelvis posture (tilt or rotation) correction parameters (CP) for cup anteversion can be calculated and the accuracy of cup anteversion assessment can be improved[3, 4]. METHODS Six subjects were recruited to receive pelvis CT scans with IRB approval. With CT data and cup CAD models as input, Analyze, a medical imaging software, was applied to create a 3D pelvis model. The pelvis model was then realigned according to Lewinnek’s study, which suggested orienting the anterior pelvic plane (APP) parallel to coronal plane. Cup placements were simulated in 15 positions relative to APP in every subject, including cup inclination of 30°, 40° and 50° coupled with anteversion of -5,° 5°, 15°, 25° and 35°, respectively (Figure 1).