Accuracy of Cup Alignment in Total Hip Arthroplasty: A Comparison Between Portable Navigation and Goniometer.

Background Navigation systems, including portable navigation systems, used for total hip arthroplasty (THA) are useful for achieving higher cup alignment accuracy. NAVBIT, a newly available portable navigation system, uses a unique registration method, the table tilt registration. However, its accuracy is unclear. This retrospective study aimed to investigate whether THA with a portable navigation system in the lateral position with the flip technique is more accurate than THA with a cup goniometer in the supine or lateral positions. Methodology This study included 96 consecutive patients (77 women, 19 men) who underwent primary cementless THA using either a portable navigation system in the lateral position with the flip technique or a cup goniometer in the supine or lateral positions. The average age of the patients was 66.8 years (range = 29-91) and the average body mass index was 24.6 kg/m (range = 17.5-39.9). The accuracy of cup orientation was compared among the three groups. Results The absolute values of the difference in cup inclination and anteversion with the NAVBIT (2.1 ± 1.7°, 2.0 ± 1.4°) were smaller than that with the cup goniometer in the supine (3.4 ± 2.4°, 3.4 ± 2.2°) and lateral decubitus positions (3.4 ± 2.5°, 5.0 ± 3.5°). Overall, 91%, 64.5%, and 56.3% were within 5° of the target angles in the navigation, supine goniometer, and lateral goniometer groups, respectively. Conclusions The accuracy of cup alignment with the portable navigation system using the flip technique was significantly higher than that with the cup goniometer in the supine and lateral decubitus positions.