Variability in femoral component rotation reference axes measured during navigation-assisted total knee arthroplasty...

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 degrees +/- 3.67 degrees (mean +/- SD; range, -7 degrees to 10.5 degrees), 3.90 degrees +/- 4.17 degrees (mean +/- SD; range, -3 degrees to 15.5 degrees), and -4.03 degrees +/- 2.71 degrees (mean +/- SD; range, -9.5 degrees to 1.0 degrees), respectively. The coefficients of variation (SD/mean x100) 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.