The anterior surface of the femur as a new landmark for femoral component rotation in total knee arthroplasty.

Femoral component rotation is very important in avoiding complications and maximizing knee function following total knee arthroplasty. There is continuing debate over the most accurate axis to select intraoperatively to obtain the best results. There is considerable doubt over the ability of commonly used bony landmarks to produce a line parallel to the flexion-extension axis of the femur, either due to anatomical variation or due to poor reproducibility of the axes. Computer navigation was used to accurately measure the relative rotation indicated intraoperatively between bony landmarks, including a previously uninvestigated axis on the anterior surface of the femur. Measurements were taken during 193 total knee arthroplasties. There was a significant association between the Whiteside's Line and the axis on the anterior surface of the femur. The Posterior Condlylar Axis was extremely variable when compared with the other measurements, with a wide range centered on a mean value of 4.1 degrees internally rotated to the perpendicular of Whiteside's Line. There were significant differences in both the Posterior Condylar Axis and Anterior Femoral Axis when comparing varus and valgus knees. The Posterior Condylar Axis was shown to be an inconsistent measurement in comparison to other bony landmarks, particularly in valgus knees. The strong correlation between the Whiteside's Line and the Anterior Femoral Axis raises the possibility that the Anterior Femoral Axis maybe a useful landmark in identifying correct femoral component rotation.