Comparison of accuracy of cup position using portable navigation versus alignment guide in total hip arthroplasty in supine position

Background: Accelerometer-based portable navigation systems in supine total hip arthroplasty (THA) have been developed, but there are no reports on the accuracy of cup placement. We aimed to investigate and compare the accuracy of the accelerometer-based portable navigation system versus the acetabular alignment guide placed on the pelvis in THA using the direct anterior approach (DAA). Both devices tracked changes in the pelvic position. Methods: In this single-centre, retrospective study, we reviewed 115 hips in 113 patients who underwent primary THA via the DAA using an accelerometer-based portable navigation system in the supine position (portable navigation group) and 106 hips in 101 patients who underwent THA using an acetabular alignment guide (alignment guide group) as controls. Hips were evaluated postoperatively using computed tomography to measure cup orientation. The accuracy of cup orientation was compared between the 2 groups. Results: Absolute values of inclination error were 3.1 degrees +/- 2.2 degrees and 2.9 degrees +/- 2.3 degrees (p = 0.708) in the portable navigation and alignment guide groups and those of anteversion error were 2.8 degrees +/- 2.3 degrees and 3.7 degrees +/- 2.7 degrees, respectively (p = 0.005). The number of cups placed within 10 degrees of error was 98.3% and 96.2% in the portable navigation and alignment guide groups, respectively (p = 0.304). The portable navigation group had significantly more hips (72.2%) placed within a 5 degrees margin of error than did the alignment guide group (56.6%) (p = 0.016). Conclusion: High accuracy in cup placement was achieved using accelerometer-based portable navigation in supine THA. Using a navigation system may contribute to improved long-term outcomes.