Variability in Femoral Component Rotation Reference Axes Measured During Navigation-Assisted Total Knee Arthroplasty Using Gap Technique

The basic objective in total knee arthroplasty is to achieve the correct amount of femoral component rotation, and this can be achieved either with a measured resection technique or indirectly with a flexion/extension gap equalization technique. We studied variability in the reference axes (posterior condylar axis, Whiteside's line, transepicondylar axis) when soft tissue tension was managed intraoperatively using a navigation system. The mean angles for the transepicondylar line, Whiteside's line, and the posterior condylar line from the proximal tibia resection plane were 1.29° ± 3.67° (mean ± SD; range, −7° to 10.5°), 3.90° ± 4.17° (mean ± SD; range, −3° to 15.5°), and −4.03° ± 2.71° (mean ± SD; range, −9.5° to 1.0°), respectively. The coefficients of variation (SD/mean ×100) for these 3 variables were 283%, 106%, and 67%, respectively. Of the 3 reference axes used widely for femoral component rotation, the angles from the posterior condylar line to the proximal tibia resection plane showed the smallest range of variance.