Accuracy of cup placement using computed tomography-based navigation system in total hip arthroplasty through the direct anterior approach

Background: This study aimed to elucidate the accuracy of cup placement with the computed tomog-raphy (CT)-based navigation system (CTN) in the direct anterior approach (DAA)-total hip arthroplasty (THA) in the supine position compared with the mechanical cup alignment guide (MG) or the fluoros-copy (FS).Methods: A total of 171 hips of 156 patients undergone primary THA were classified into the following three groups (the MG group: 63 hips, the FS group: 58 hips, the CTN group: 50 hips). Comparing the preoperative planning with postoperative CT measurement by three-dimensional templating software, the accuracy of cup placement was investigated in the three groups.Results: There were significant differences in the mean absolute error of radiographic inclination (RI) between the MG group (4.4 degrees +/- 3.2 degrees) and the CTN group (2.8 degrees +/- 2.5 degrees) (p = 0.01). The mean absolute error of radiographic anteversion (RA) also showed significant differences between the CTN group (2.8 degrees +/- 1.9 degrees) and the MG group (5.8 degrees +/- 4.7 degrees) (p = 0.0001) or the FS group (4.8 degrees +/- 4.1 degrees) (p = 0.02). Regarding the cup center position, the mean absolute error of vertical position from preoperative planning was the smallest in the CTN group (1.8 +/- 1.4 mm) compared with those in other groups (MG: 3.3 +/- 3.2 mm, p = 0.007, FS: 3.2 +/- 3.0 mm, p = 0.017).Conclusion: The CTN guarantees accurate cup placement in the DAA-THA in the supine position compared with the MG and FS groups.(c) 2021 The Japanese Orthopaedic Association. Published by Elsevier B.V. All rights reserved.