A Comparative Study of Surgical Approach, Patient Positioning and Cup Positioning Technique - Cup Orientation Using 2D/3D-matching Technique HipMatch in 349 Hips

Introduction: Postoperative measurement of cup orientation on pelvic radiographs is prone to error, while CT scans are less practical in routine settings. The 2D/3D-matching technique allows measurement of cup orientation normalized to anterior pelvic plane using standard radiographs. This study aimed to determine the (1) precision and (2) percentage of outliers in cup orientation among three groups with different surgical approaches, patient positioning, and cup positioning techniques. Methods We retrospectively analyzed 322 patients (349 hips) who underwent total hip arthroplasty (THA) with three different approaches: the 'direct lateral' group (66 hips) using a lateral position and direct lateral approach; the 'supine anterior' group (128 hips) using a supine position and anterior approach; and the 'lateral anterior' group (155 hips) using a lateral position and anterior approach. Cup positioning was determined intraoperatively using a mechanical device in the ‘direct lateral’ and ‘lateral anterior’ groups and using fluoroscopy in the ‘supine anterior’ group. The 2D/3D-matching technique, HipMatch, was used to measure cup inclination and anteversion on postoperative radiographs normalized to the anterior pelvic plane. Precision was assessed using standard deviations (SDs), with outliers defined as orientations outside 2 SDs (31–56° inclination, 7–36° anteversion). Results (1) The ‘supine anterior’ group showed the highest precision for inclination (SD = 4.6°) compared to the ‘direct lateral’ (SD = 6.8°) and ‘lateral anterior’ (SD = 6.2°) groups (p < 0.001). Precision for anteversion did not differ significantly (p = 0.097). (2) The percentage of outliers did not significantly differ among the groups (p = 0.183 to 0.384). Conclusion Inclination and anteversion vary with surgical approach, patient positioning in this largest series of APP normalized cup position measurements. The highest precision for inclination was seen in the anterior approach in supine position with fluoroscopy but approach, positioning, and technique did not affect the percentage of outliers.