The transepicondylar axis or the posterior condylar axis: Which is the best reference for femoral component rotation in robotic-assisted total knee arthroplasty?

Objective For robotic-assisted total knee arthroplasty (TKA), accurate identification of landmarks may have a direct impact on the displayed value for femoral component rotation. The aim of this study was to determine the effects of landmark identification by different surgeons on the consistency of the displayed values of the TEA (the angle between the transepicondylar axis and the femoral component axis) and PCA (the angle between the posterior condylar axis and the femoral component axis). Methods The anatomical data of 56 patients who underwent robotic-assisted TKA at our institution and whose landmarks (the transepicondylar axis and the posterior condylar axis) were identified by the two surgeons using the MAKO TKA system . After the data were standardized, the TEA value when the PCA was adjusted to 0° was recorded as α , and the PCA value when the TEA was adjusted to 0° was recorded as β . The measured value was α ₁ β ₁ for Surgeon-1 and α ₂ β ₂ for Surgeon-2. The values of α and β are defined as positive for external rotation and negative for internal rotation. Results The ICC consistency test of α was 0.761, and that of β was 0.943. Our data revealed that 26.8% of the ∆ α ( α ₁ - α ₂ ) values were > 2°, 42.9% were within 1°, 5.4% of the ∆ β ( β ₁ - β ₂ ) values were > 2°, and 80.4% were within 1°. Conclusion The posterior condylar axis was significantly more consistently identified than the transepicondylar axis was during robotic-assisted TKA by different surgeons. To avoid inappropriate femoral component rotation due to inaccurate identification, the surgeon should check the position of the landmarks, especially in patients who have anatomical abnormalities. Level of Evidence Level III, diagnostic study.