Image-based robotic-assisted total hip arthroplasty through direct anterior approach allows a better orientation of the acetabular cup and a better restitution of the centre of rotation than a conventional procedure.

PURPOSE: The aim was to investigate the contribution of robotics assisted total hip arthroplasty (THA) through direct anterior approach (DAA) in improving radiographic precision, functional results and complications. METHODS: This retrospective study compared 100 primary conventional THA (cTHA) to 50 primary robotic THA (rTHA) through DAA. All cups were placed with the objective of having no anterior overhang while respecting the safe zones (SZ). Radiographic analysis included cup inclination and anteversion, vertical and horizontal changes of the rotation centre (ΔVCOR, ΔHCOR), acetabular and femoral offset. SZ were 30-50° of inclination and 10-30° of anteversion. Outliers were defined as medial displacement of the COR > 5 mm, vertical displacement of the COR > 3 mm superiorly. Harris hip score (HHS) and complications were compared at one year of follow-up. RESULTS: The robotic cups were better oriented with 98% in the global SZ versus 68% in the cTHA group (p = 0.0002). The COR was on average better restored in the robotic group in both the horizontal and vertical planes (Δ HCOR = - 5.0 ± 5.0 vs - 3.4 ± 4.9, p = 0.03; Δ VCOR = 1.6 ± 3.3 vs 0.2 ± 2.7, p = 0.04). There were fewer outliers in the rTHA group concerning VCOR (28% versus 10%, p = 0.03). There was no significant difference in HHS and complication rate at one year. CONCLUSION: The use of robotics for THA by DAA provided an advantage in controlling the orientation of the cup and the restoration of its rotation centre. Thanks to the 3D planning on CT scan, it allowed to respect the thresholds while avoiding the anterior overhangs.