Robotic-Arm Assisted versus Conventional Total Hip Arthroplasty via the Direct Anterior Approach: Acetabular Cup Positioning, Limb-Length Discrepancy, and Offset Restoration

Background Robotic-arm assisted total hip arthroplasty (THA) aims to improve the precision of acetabular cup placement and limb-length restoration. Whether these radiographic advantages translate into clinically meaningful benefits over conventional THA via the direct anterior approach (DAA) remains incompletely characterized. Methods We retrospectively reviewed 330 consecutive patients who underwent primary unilateral THA via the DAA by a single surgeon-led team between January 2021 and January 2025 at a tertiary referral center. In total, 165 patients received MAKO robotic-assisted THA and 165 underwent conventional THA. Indications included osteonecrosis of the femoral head, developmental dysplasia of the hip, rheumatoid arthritis, osteoarthritis, ankylosing spondylitis, and femoral neck fracture. All postoperative radiographic measurements were performed independently by two attending radiologists using a picture archiving and communication system. Primary outcomes comprised acetabular anteversion and inclination, leg-length discrepancy (LLD), and hip offset parameters. Secondary outcomes included Lewinnek and Callanan safe-zone compliance, rates of absolute LLD exceeding 5 mm and 10 mm, total intraoperative blood loss, operative time, complications, and Harris Hip Scores (HHS) at a maximum follow-up of 3 years. Results Baseline demographics were well matched between groups (all P > 0.05). The robotic group demonstrated significantly greater accuracy in acetabular cup placement, with 94.6% of cups within the Lewinnek safe zone versus 84.2% in the conventional group (P = 0.004; OR = 3.24). The proportion of patients with absolute LLD > 5 mm was markedly lower in the robotic group (15.8% vs. 38.2%; P < 0.001; OR = 0.30). No between-group differences were observed for the Callanan safe zone, severe LLD (> 10 mm), or individual offset parameters. Robotic-assisted THA was associated with longer operative time (118.5 vs. 97.8 min; P < 0.001) and greater total intraoperative blood loss (285.6 vs. 160.3 mL; P < 0.001). HHS at final follow-up was comparable between groups (90.5 vs. 90.1; P > 0.05). Conclusions Robotic-arm assisted DAA THA improves the precision of acetabular cup positioning within the Lewinnek safe zone and reduces the incidence of moderate limb-length discrepancy compared with conventional THA. These radiographic gains are achieved at the expense of longer operative time and greater blood loss, with no detectable difference in short-term functional outcomes. Long-term studies are needed to determine whether these improvements translate into reduced dislocation rates and improved implant survivorship.