Relationship between pelvic morphology and functional parameters in standing position for patient-specific cup planning in THA

Abstract

The sagittal orientation of the pelvis commonly called pelvic tilt has an effect on the orientation of the cup in total hip arthroplasty (THA). Pelvic tilt is different between individuals and changes during activities of daily living. In particular, the pelvic tilt in standing position should be considered during the planning of THA to adapt the target angles of the cup patient-specifically to minimize wear and the risk of dislocation. Methods to measure pelvic tilt require an additional step in the planning process, may be time consuming and additional devices or x-ray imaging are necessary.In this study, the relationship between three functional parameters describing the sagittal pelvic orientation in standing position and seven morphological parameters of the pelvis was investigated. Correlations might be used to estimate the pelvic tilt in standing position by the morphology of the pelvis in order to avoid additional measuring techniques of pelvic tilt in the planning process of THA. For 18 subjects a semi-automatic process was established to match a 3D-reconstruction of the pelvis from CT scans to orthogonal EOS imaging in standing position and to calculate the morphological and functional parameters of the pelvis subsequently.The two strongest correlations of the linear correlation analysis were observed between morphological pelvic incidence and functional sacral slope (r = 0.78; p = 0.0001) and between morphological pubic symphysis-posterior superior iliac spines- ratio and functional tilt of anterior pelvic plane (r = -0.59; p = 0.0098). The results of this study suggest that patient-specific adjustments to the orientation of the cup in planning of THA without additional measurement of the sagittal pelvic orientation in standing position should be based on the correlation between morphological pelvic incidence and functional sacral slope.