Robotic Arm–Assisted Total Knee Arthroplasty Results in Smaller Femoral Components and Larger Tibial Baseplates Than the Manual Technique

Background: Robotic systems for total knee arthroplasty (TKA) may utilize computed tomography three-dimensional modeling and intraoperative ligamentous balancing data to assist surgeons with implant size and position. This study evaluated the effect of such robotic systems on implant selection. Methods: We reviewed 645 TKAs performed with a single prosthetic design at 2 academic medical centers between 2016 and 2022. A robotic system was utilized in 304 TKAs, 341 were conventionally instrumented. Implant sizing was compared between cohorts. Multivariate analyses assessed for confounding and effect modification on the basis of demographics. Results: The 2 cohorts exhibited no significant differences in age (P = .33), weight (P = .29), or race (P = .24). The robotic-arm cohort had fewer women (58.9% vs 66.7% P = .04) and was taller on average (66.3 in vs 65.0 in P < .001). Mean polyethylene liner thickness was larger in the manual cohort (10.3 robotic and 10.6 manual; P < .00). On multivariate analysis, robotic-arm TKAs had larger tibial components (P < .001) and smaller femoral components (P = .017). Conclusions: Robotic-arm assisted TKA with computed tomography–based three-dimensional planning was associated with a larger mean tibial component size and a smaller mean femoral component size when compared to conventionally instrumented TKAs. Observed differences likely reflect differences in the data informing implant size selection; effects on clinical outcomes warrant further study.