Femoral components are positioned in greater external rotation using functional alignment in robot-assisted total knee arthroplasty compared to mechanical alignment.

PURPOSE

Objective of this study was to evaluate the effect of functional alignment on femoral component rotation compared to mechanical alignment in knees with a constitutional tibial varus alignment classified as coronal plane alignment of the knee (CPAK) types I, II and IV.

METHODS

This retrospective study included patients undergoing conventional total knee replacement (TKR) ( = 64) and robot-assisted TKR ( = 84). Coronal and axial measurements were performed manually and automatically using pre- and postoperative computed tomography images in the conventional group and robot-assisted group respectively.

RESULTS

Femoral component rotation was statistically significant more external rotated in the conventional group versus robot-assisted group (1.3° ± 2.7° vs. 0.76° ± 1.4°,  < 0.001). Also, the tibial plateau was placed statistically significant more in varus in the robot-assisted group compared to the conventional group (87.6° ± 2.5° vs. 88.9° ± 1.4°,  < 0.001).

CONCLUSION

Functional alignment leads to more varus of the tibial component and less external rotation of the femoral component compared to mechanical alignment in TKR in patients with a constitutional tibial varus alignment. Since this is a radiological analysis, further research is needed to understand how these differences affect clinical outcomes as faster recovery, adequate patellar tracking and longer survival.

LEVEL OF EVIDENCE

Level III.