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Introduction: Little is known about the association between well-fixed polished tapered cemented stems (PTCS) implanted by the line-to-line technique and changes of stem migration, or the change of functional anteversion of the femur after total hip arthroplasty (THA). Materials and methods: This retrospective study included 422 two-stage bilateral primary THAs performed using PTCS implanted by the line-to-line technique. CT scans were made on both the target side (first postoperative CT) and on the contralateral side (second postoperative CT) 1 week postoperatively. The mean follow-up was 7.8 months. CT data for each scan were transferred to 3D template software (Zed hip, Lexi, Japan). The postoperative changes of anatomical stem anteversion (ASA), functional femoral anteversion (FFA), and stem subsidence were evaluated. Results: A total of 20 THAs with CT scans were available on 3D template software. The ASA and the FFA had migrated − 0.68° ± 0.62° and − 5.5° ± 9.7°, respectively, over the follow-up period. A significant positive correlation was observed between the change of subsidence and ASA (r2 = 0.34, p = 0.007), between the FFA on the second postoperative CT and ASA on the first postoperative CT (r2 = 0.26, p = 0.02) and between the FFA on the second postoperative CT and FFA on the first postoperative CT (r2 = 0.52, p = 0.0003). Conclusion: This study indicates that the change in axial rotation of a PTCS implanted by the line-to-line technique was less than that reported by other studies and the preoperative external rotation contracture was substantially improved after THA. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to clarify the difference in implant alignment between the direct anterior approach (DAA) and the anterolateral approach in the supine position (ALS).Methods: A retrospective comparative study consisted of 215 consecutive primary total hip arthroplasties using tapered polished and straight cemented-stems via two different minimally invasive approaches (DAA group in 106 hips and ALS group in 109 hips).Results: The cup radiographic anteversion angle was significantly lower in the ALS group than in the DAA group (12.9° versus 16.9°, p = 0.001). The frequency of the safe zone tended to be more favourable in the ALS group than in the DAA group (95% versus 87%, p = 0.052). Stem alignment in the sagittal plane was significantly better in the ALS group than in the DAA group (84% versus 71%, p = 0.022).Conclusions: Both cup and stem alignments were better in the ALS group than the DAA group. [ABSTRACT FROM AUTHOR]