Acetabular component placement accuracy and short-term outcomes in total hip arthroplasty

Aims: Precise acetabular component positioning is critical to the success of total hip arthroplasty (THA). Mako uses CT-based robotic assistance, whereas AR-hip is an augmented reality-based portable navigation system operating without preoperative CT and at lower costs. Although both systems improve accuracy, direct comparative data are scarce. We compared cup placement accuracy and short-term outcomes between Mako robotic arm and AR navigation systems. Methods: This single-centre retrospective cohort study included 192 primary THAs (Mako, 147; AR navigation, 45). Cup placement accuracy was assessed three-dimensionally using postoperative CT, evaluating cup alignment (radiological inclination (RI) and anteversion (RA)) and position (centre of rotation (COR)). Short-term outcomes were evaluated using the Harris Hip Score (HHS), Japanese Orthopaedic Association hip score (JOA), Japanese Hip-disease Evaluation Questionnaire (JHEQ), Timed Up and Go (TUG), and 10 m walk test (10MWT). Baseline differences were adjusted using propensity score overlap weighting. Results: Mako demonstrated significantly superior accuracy than AR navigation, with smaller absolute errors in cup angles (RI 2.0° vs 3.0°, p = 0.045; RA 1.7° vs 2.4°, p = 0.005) and COR errors in the superior-inferior direction (1.5 mm vs 3.7 mm, p < 0.001). More cases were within 5° of planned angles with Mako (92.3% vs 77.7%, p = 0.030), while Lewinnek safe zone rates were high in both groups (99.5% vs 95.2%, p = 0.202). Short-term clinical scores and functional recovery at discharge were similar between groups. Operating time and blood loss were greater with Mako (122.6 vs 103.5 mins; 242.5 vs 171.5 ml; both p < 0.001). Subgroup analyses showed greater advantages of Mako in complex cases, such as obesity and developmental dysplasia of the hip, although interactions were insignificant. Conclusion: Mako demonstrated superior cup placement accuracy and COR reconstruction compared with AR navigation, with comparable short-term clinical outcomes, potentially offering advantages in complex cases. However, further research is warranted to clarify its long-term outcomes and cost-effectiveness.