Revision Total Hip Arthroplasty Using Imageless Navigation With the Concept of Combined Anteversion

Background: The purpose of the study was to evaluate the implant positions and clinical results of revision total hip arthroplasty (THA) using an imageless navigation with the concept of combined anteversion. Methods: A total of 40 cementless revision THAs (24 men and 16 women) using an imageless navigation with the concept of combined anteversion were retrospectively evaluated. The concept of combined anteversion was applied in cup positioning based on Widmer's equation (cup anteversion + 0.7 x stem anteversion). The mean follow-up period was 80.7 months. Postoperatively, the inclination of the cup was evaluated on standard anteroposterior view of the radiograph, and the anteversion of the cup and femoral stem was evaluated using computed tomography scan. A cup inclination of 40 degrees +/- 10 degrees and combined anteversion of the cup and femoral stem of 37 degrees +/- 10 degrees based on Widmer's equation were regarded as the "safe zone." Results: The average anteversion of the revised femoral stems was 15.3 degrees +/- 2.9 degrees (range, 9.5 degrees-21.5 degrees), whereas that of the remained femoral stems was 17.4 degrees +/- 9.7 degrees (range, 4.2 degrees-29.8 degrees). The inclination, anteversion of the cup, and combined anteversion after revision THA were 42.3 degrees +/- 3.1 degrees (range, 32.1 degrees- 48.2 degrees), 25.0 degrees +/- 2.9 degrees (range, 16.9 degrees-29.5 degrees), and 36.1 degrees +/- 3.4 degrees (range, 27.2 degrees-42.9 degrees), respectively. Therefore, the position of the implants, relative to the safe zone, showed no outliers after the revision surgery. Neither dislocation nor osteolysis was observed after the surgery. Conclusion: Favorable results of this study indicate that imageless navigation helps the surgeon in placing the components of revision THA in the safe zone. This study also shows that when this safe zone is consistently obtained, then no postoperative dislocations were observed in these patients over the 6-year follow-up period. (C) 2016 Elsevier Inc. All rights reserved.