Cup positioning in primary total hip arthroplasty using an imageless navigation device: is there a learning curve?

In this study, the success of cup positioning in total hip arthroplasty (THA) using an imageless navigation system was analyzed (1) during the learning period and (2) after the learning period for using the navigation system. Sixty THAs were performed in which threaded cups were placed with use of a computer-assisted navigation device (B. Braun Aesculap, Tuttlingen, Germany). Half of the procedures (30), group A, were done by the same surgeons under the learning curve for using the navigation system; the other half (30), group B, were done by surgeons who were no longer considered under the learning curve. Intraoperative acetabular component parameters (inclination, anteversion) for both groups were compared with postoperative radiographic alignment values. In group A, significant differences were seen between intraoperative and postoperative cup orientation. In group B, no significant differences were seen between intraoperative and postoperative cup orientation. Additionally, the percentage of outliers decreased in group B. Operating and anesthesia times significantly decreased with the surgeon's experience in imageless cup navigation. There was an individual increase of precision during the learning curve for all surgeons. Imageless navigation is a dependable and accurate method of cup positioning during THA. However, accuracy of cup placement and length of operating room time were affected by surgeons' experience using the system. Imageless navigation may lead to a reduction in the length of the learning curve for surgeons beginning to perform THAs, improvement in the surgeon's ability to perform this procedure safely, and minimization of outliers.