Robotic-assisted total knee arthroplasty reduces alignment variability and rotational outliers compared with conventional techniques.

INTRODUCTION

Precise component positioning in total knee arthroplasty (TKA) influences tibiofemoral mechanics, patellofemoral tracking, and soft-tissue balance. Although robotic-assisted TKA improves alignment accuracy, most comparative studies emphasize mean alignment rather than surgical reproducibility. Variability and outlier rates may better reflect precision. This study compared alignment variability and the proportion of coronal and rotational outliers between robotic-assisted and conventional TKA performed under identical mechanical alignment targets.

METHODS

A retrospective comparative cohort included 300 primary TKAs (150 robotic-assisted, 150 conventional) performed by the same surgical team between 2022 and 2025. Postoperative hip-knee-ankle (HKA) alignment was measured on standardized long-leg radiographs. Rotational alignment was evaluated by computed tomography in a predefined subgroup. Variability was quantified using standard deviation and equality of variance tested with the Brown-Forsythe method. Outliers were defined as deviation > 3° from target alignment. Multivariable logistic regression identified predictors of outlier status.

RESULTS

Mean postoperative HKA did not differ between groups (0.4° ± 1.6° robotic vs. 0.6° ± 2.8° conventional; p = 0.41). Robotic-assisted TKA showed lower dispersion (SD 1.6° vs. 2.8°; p < 0.001). Coronal outliers occurred in 6.7% of robotic cases versus 21.3% of conventional cases (p < 0.001). Rotational mismatch > 3° was less frequent with robotic assistance (8.7% vs. 24.0%; p = 0.006).

CONCLUSIONS

Robotic-assisted TKA reduced alignment variability and outliers without altering mean alignment, suggesting improved surgical reproducibility.