MDCT image based assessment of acetabular cup orientation in total hip arthroplasty

Total hip arthroplasty (THA) is an orthopaedic surgery which replaces the damaged hip joint with implants. The acetabular cup is implanted to the acetabulum. Some studies show that the outcome of THA is strongly correlated to the orientation of the acetabular cup. This paper proposes a fully automated method for measuring the orientation using multidetector-row computed tomography (MDCT) images. The method defines the pelvic anatomical coordinate system using anterior pelvic plane (APP), and measures angles between the cup implanting axis and the pelvic anatomical coordinate axis. The angles are inclination angle and anteversion angle. The method was applied to two phantoms in which the acetabular cup was implanted to the artificial bone. We acquired multiple set of MDCT image for the same phantom with changing the pelvic pose in the MDCT scanner to evaluate the reproducibility. The standard deviations of measured angles in multiple acquisitions were less than 2.0 deg for both of the inclination and the anteversion angles.