• Shunsaku Nishihara and Kenji Hayashida.
• Department of Orthopaedic Surgery, Daini Osaka Police Hospital, 2-6-40 Karasugatsuji, Tennouji-ku, Osaka, 543-8922, Japan. shu-nishihara@umin.net.
• Arch Orthop Trauma Surg. 2022 Feb 1; 142 (2): 323329323-329.

IntroductionIn total hip arthroplasty (THA), improper cup orientation can result in dislocation, early excessive polyethylene wear, and pain following THA. The supine position during THA provides a more reproducible functional pelvic position than the lateral decubitus position and may allow freehand cup placement as reliable as that obtained by computer navigation. The purpose of this study was to investigate the accuracy of freehand cup placement through a supine direct anterior approach (DAA) compared with computed tomography (CT)-based navigation.Materials And MethodsThe same surgeon performed primary cementless THA through the DAA in 144 supine patients. Seventy-two patients underwent freehand cup placement with standard mechanical guidance-oriented radiographic target cup positioning, and 72 underwent placement with CT-based navigation guidance. Using three-dimensional templating software, the study group calculated cup inclination and anteversion on postoperative CT scans.ResultsThe navigation method resulted in a significantly smaller deviation of inclination from the target (p < 0.05); the difference in anteversion was not significant. In addition, the navigation method resulted in significantly fewer cups placed ± 10° outside the target position (0% for inclination, 0% for anteversion) than did the freehand procedure (26% for inclination, 25% for anteversion) (p < 0.0001).ConclusionsFreehand cup placement is less reliable even in the supine position. Use of a CT-based navigation system can significantly improve cup positioning in THA through the DAA by reducing the incidence of outliers.© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.

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