How accurate is Whiteside's line as a reference axis in total knee arthroplasty?

There is an increasing focus on the precision with which prostheses in the knee are inserted with advent of computer assisted surgery. Much attention has been paid to the differences between this and conventional alignment jig techniques. Both techniques however rely on accurate identification of bony morphology and utilising this information to correctly orientate the prosthesis. Correct rotational alignment of the femoral prosthesis in total knee arthroplasty is important for correct patella tracking, patellofemoral joint contact forces, varus-valgus positioning in flexion, correct rotational alignment of the tibia in extension and the avoidance of anterior femoral notching. Whiteside's line is considered to be perpendicular to the epicondylar axis and therefore a reliable axis of reference. A cadaveric study was performed to assess the reliability and reproducibility of Whiteside's line in 50 cadaveric distal femora. Our results have shown that Whiteside's line is perpendicular to the epicondylar axis in the majority of cases (mean of 91 degrees). However the variation of values about the mean (range 80-102 degrees), and a SD of 4.7 degrees suggests that this should not be used alone as a rotational assessment guide. Rotation should ideally be checked against several axes to avoid errors in rotation positioning of the femoral prosthesis.