Femoral rotational alignment, based on the anteroposterior axis, in total knee arthroplasty in a valgus knee. A technical note.

The landmarks used to achieve correct rotational alignment of the femoral component in total knee arthroplasty may be indistinguishable or unreliable in the distal architecture of a valgus knee. Five observers identified the anteroposterior axis, the posterior condylar axis, and the transepicondylar axis in thirty cadaveric femora to determine the reliability of the use of each axis in the operative setting. In addition, radiographs were made of the distal aspect of each femur, the axes were constructed, and the angles were measured and compared with the visual measurements made by the observers. A line drawn perpendicular to the anteroposterior axis consistently approximated 4 degrees of external rotation relative to the posterior condylar surfaces. The transepicondylar axis was more difficult to define and was not as accurate. The radiographic results were similar to the visual results, but the standard deviations for the former were less than those for the latter. The anteroposterior axis appears to be a reliable landmark for rotational alignment of the femoral component in a valgus knee.