Increased Accuracy of Acetabular Cup Positioning with an Automatic Impaction Device in Total Hip Arthroplasty.

Background: Traditionally, cementless total hip arthroplasty (THA) has been primarily performed using a manual technique involving a hammer and an impactor. During cup insertion into the acetabulum, the manual technique may cause temporary limitations in visualization, discrepancies in the applied force, and imbalances in the force vector. Recently, automatic impaction devices have been developed and adopted for cup insertion. The purpose of this study was to compare the accuracy of cup positioning in primary THA between the manual technique and the use of an automatic impaction device. Methods: A total of 67 hips that underwent primary THA were retrospectively evaluated: 36 hips using the manual technique and 31 hips using an automatic impaction device. The accuracy of acetabular cup positioning between the 2 groups was compared using the Lewinnek safe zone, which indicates accurate cup placement, based on postoperative measurements of cup anteversion and inclination angle. Six methods for measuring anteversion were applied in this study. In addition, the incidence of acetabular screw augmentation and the occurrence of intraoperative and postoperative complications up to 1 year after surgery were assessed. Results: The proportion of cases positioned within the Lewinnek safe zone was higher in the automatic group than in the manual group across all measurement methods. Regarding postoperative complications, 1 episode of dislocation occurred in the manual group, but the difference between the groups was not statistically significant. Conclusions: An automatic impaction device can improve the accuracy of THA cup positioning compared with the manual technique.