Comparing cup implantation errors in total hip arthroplasty following rotational acetabular osteotomy: computed tomography-based navigation versus robotic arm-assisted system

Robotic arm-assisted total hip arthroplasty (THA) has been reported to achieve acetabular cup implantation that more accurately reproduces the preoperative plan than computed tomography (CT)-based navigation. However, whether this superiority applies in technically demanding cases, such as THA following pelvic osteotomy, remains unclear. Therefore, we evaluated the cup-positioning errors in THA performed with these technologies in patients who had previously undergone rotational acetabular osteotomy (RAO). Twenty-three patients (24 hips) underwent navigated THA between January 2017 and January 2021 (Navigation group), and 22 patients (24 hips) underwent robotic-assisted THA between February 2021 and February 2023 (Mako group). The error between preoperative planning and postoperative results was calculated and compared between the groups. The absolute values of errors in cup orientation (radiographic inclination and anteversion) and position (mediolateral, anteroposterior, and superoinferior axes) were assessed. All absolute errors, except for the superoinferior axis in the Navigation group (3.4 ± 3.5 mm), were within 3° or 3 mm, indicating high accuracy. The absolute error in radiographic inclination was significantly lower in the Mako group than in the Navigation group (0.8 ± 0.8° versus 1.9 ± 1.3°; p = 0.005), whereas errors in radiographic anteversion and position did not differ significantly between the groups. No cup-related complications were noted in either group. From baseline to 2 years postoperatively, the Japanese Orthopaedic Association hip score improved significantly in the Navigation group (from 46.0 ± 9.3 to 89.7 ± 5.9) and the Mako group (from 50.0 ± 12.6 to 93.3 ± 5.8) (both p < 0.001), demonstrating satisfactory clinical outcomes. In technically demanding THA after RAO, CT-based navigation and robotic-assisted systems demonstrated comparable acetabular cup placement errors and satisfactory short-term clinical outcomes. Although robotic-assisted THA was associated with a significantly smaller error in radiographic inclination, overall cup placement errors did not differ significantly between the two technologies.