Achieving Safe Zone Cup Positioning in Total Hip Arthroplasty using Anatomical Landmarks: A Prospective Computed Tomography-based Evaluation

Introduction: Accurate orientation of the acetabular component in total hip arthroplasty (THA) is critical for restoration of hip biomechanics and prevention of complications such as instability, impingement, accelerated wear, and early implant failure. While computer-assisted navigation enhances accuracy, its routine use is limited by cost and availability. Anatomical landmarks, including the anterior acetabular notch (AAN) and transverse acetabular notch (TAN), may provide a reliable intraoperative reference for component positioning. This study evaluates the accuracy of acetabular cup placement using these landmarks with post-operative computed tomography (CT)-based assessment. Materials and Methods: A prospective observational study was conducted on 53 patients undergoing primary total hip replacement at a tertiary care center. Acetabular component positioning was guided intraoperatively using AAN for anteversion and TAN for abduction. Post-operative CT scans obtained on day 14 were used to measure cup orientation. Target alignment was defined according to Lewinnek's safe zone (abduction 40° ± 10°, anteversion 15° ± 10°). Functional outcomes were assessed using the Harris Hip Score (HHS), and patients were followed up clinically and radiologically. Results: The mean post-operative acetabular cup abduction was 40.13° and anteversion was 16.29°, both within the defined safe zones. The mean HHS improved significantly from 37.42 preoperatively to 85.83 postoperatively, indicating substantial functional recovery. The mean error in cup positioning was markedly reduced post-operatively. No cases of dislocation or major complications were observed during the follow-up period. Conclusion: Simple anatomical landmarks can reliably guide acetabular cup placement in THA, offering a cost-effective alternative to intraoperative technology-assisted guidance methods like navigation, with comparable clinical outcomes.