Can the epicondylar axis be defined accurately in total knee arthroplasty?

As part of a study on rotational alignment of the femoral component in knee replacement, the surgical epicondylar axis was identified in 74 knees and marked with pins. An alternative technique was employed to achieve rotational alignment and in each case the distance between the pins and the cut surface of the posterior condyles was measured. The alignment of the femoral component was measured postoperatively by axial CT scans of the distal femur, allowing an assessment to be made of what would have been achieved if the epicondylar pins had been used for guidance. Only 75% of knees would have been within 3 degrees of the true epicondylar axis using the epicondyles to control rotation. The error range was large (range 6 degrees ER to 11 degrees IR). Our conclusion is that even in experienced hands clinical estimation of the epicondylar axis is inaccurate and should not be relied upon as the sole determinant of femoral rotation.