Computed tomography assessment of image-free navigation-assisted cup placement in THA in an Asian population.

The authors hypothesized that an image-free navigation system would be more accurate than postoperative 3-dimensional (3-D) reconstructed computed tomography (CT) for acetabular cup inclination and anteversion during total hip arthroplasty (THA) in an Asian population. Eighty-one THAs were performed in 72 patients using the OrthoPilot image-free navigation system (B. Braun Aesculap, Tuttlingen, Germany). Cup placement position was measured by postoperative 3-D CT and compared with intraoperative navigation data. The discrepancies between the navigation data and the 3-D CT data were analyzed, as well as the correlation factors that affected the discrepancies. The discrepancies between the navigation data and the 3-D CT data were -1.5 degrees +/- 7.1 degrees (P=.04) for anteversion and -1.1 degrees +/- 7.6 degrees (P=.02) for inclination. The accuracy and precision of the anteversion discrepancies were 5.6 degrees +/- 4.4 degrees and 3.2 degrees, respectively. The accuracy and precision of the inclination discrepancies were 4.5 degrees +/- 4.4 degrees and 2.8 degrees, respectively. Five (6%) outliers existed in terms of the safe zones of anteversion and inclination. The main correlated factor among the pelvic geometry was tilt rather than rotation and obliquity of the bony anterior pelvic plane. In an Asian population, the calculated accuracy and precision of acetabular cup inclination and anteversion during THA were more reliable and the outliers were reduced using the OrthoPilot navigation system. However, discrepancies existed between intraoperative navigation data and postoperative 3-D CT data. The pelvic geometry of biometrical factors influenced the discrepancies in the navigation data.