Robotic arm–assisted total hip replacement: Assistant and mentor

Abstract

Introduction: Acetabular cup placement is vital in minimising dislocation and ensuring implant longevity in total hip arthroplasty (THA). After preoperative planning on computed tomography scans, robotic arm assistance (Mako) enables accurate acetabular bone removal and allows precise cup placement. This study compared the accuracy of cup placement between manual and robotic arm guidance. Methods: Twenty-five consecutive patients undergoing robotic THA by a single surgeon were included. All surgeries were performed using posterior approach with robotic arm–assisted acetabular reaming done by the surgeon. The surgeon, fellows, and trainees were then asked to manually position an acetabular trial into the acetabulum, attached to the robotic arm but with measurements covered. They were instructed to aim for an inclination of 40° and anteversion of 20° free of constraints. True acetabular cup was then impacted. Postoperative radiographs, intra-operative verification, and preoperative planning were compared for consistency. Results: Seventy-five manual trial cup positioning attempts were made by the surgical team. Manual cup positioning yielded a mean inclination of 40° (standard deviation=6.98°) while mean anteversion was only 16.2° (standard deviation 8.1°) despite aiming for 20°. The surgeon improved in consistency and accuracy after a learning curve of nine cases. Intraoperative verification of cup position correlated strongly with preoperative planning in both inclination (r=0.67, p=0.0003) and anteversion (r=0.75, p=0.0002). After exclusion of six rotated radiographs, postoperative anteversion correlated strongly with planning (r=0.56, p=0.018) and intra-operative verification (r=0.6, p=0.014). Conclusions: Manual acetabular cup positioning tends to produce small anteversion and a robotic arm is an excellent teacher to improve accuracy. Robotic assistance guarantees accurate cup position according to plan.