Are We All Seeing the Same Gaps while performing robotic TKA? An Inter-operator Variability Study
P. Meneguetti Filho, W.G. Lemos, T.V.D.O. Campos, M.L. Leite, R.S. Lazzarini, G.C. RodriguesObjectives:
To evaluate the inter-operator variability in manual ligament laxity assessment, specifically varus/valgus stress angles and medial/lateral gap measurements, during robotic-assisted total knee arthroplasty (rTKA) using the ROSA® Knee system, and to determine its impact on femoral component sizing agreement.
Methods:
In a comparative cross-sectional study, 21 patients underwent rTKA with the ROSA® Knee system. Two surgeons (lead surgeon and first assistant) independently performed anatomical landmark registration and gap assessments in extension (0°) and flexion (90°) under varus and valgus stress before ligament release. Absolute differences between measurements were calculated, and paired t-tests assessed statistical significance. Pearson correlation coefficients (R) evaluated agreement for stress angles and gap measurements. Cohen’s kappa determined inter-observer agreement for Artificial Intelligence ROSA® Knee system suggested femoral component size.
Results:
Strong correlations were found between operators for varus/valgus stress angles in extension (R=0.91 and 0.77, p<0.01) and flexion (R=0.46 and 0.53, p<0.05), and for medial/lateral extension gaps (R=0.59 and 0.52, p<0.01). However, no significant correlation was observed for medial/lateral flexion gaps (R=0.23 and 0.10, p>0.05). Mean discrepancies in stress angles ranged from 1.7° to 3.5°. Femoral component sizing showed substantial agreement (κ=0.70, 95% CI: 0.41–0.92).
Conclusion:
Inter-operator variability in manual gap assessment during rTKA is low in extension but significantly higher in flexion, likely due to inconsistent force application and the absence of a reproducible stop. Despite this variability, femoral component sizing agreement remains substantial. Standardized force application protocols and enhanced robotic feedback in flexion are recommended to improve reproducibility and surgical outcomes.