Evaluation of distal femoral rotational alignment according to transepicondylar axis and Whiteside's line: a study in Iranian population

Rotational positioning of femoral component is a critical aspect of total knee arthroplasty and evaluation of the landmarks for rotation of distal femur is a challenge. Most orthopedic surgeons prefer to use more available posterior femoral condyle axis, but other landmarks especially surgical transepicondylar axis may be more valid. Preoperative CT scan can help to evaluate these landmarks more accurately. The purpose of our study was to ascertain the relationships among the described axes guiding distal femur rotational alignment in CT scan of Iranian healthy population and the effects of age and gender on these relationships. Ninety cases aged between 16 and 75 years presenting with acute tibial plateau or patella fracture were included in this study. The rotation of distal femur was evaluated using the single axial CT image through the femoral epicondyles. Four lines were drawn digitally in this view: anatomical & surgical transepicondylar axes, posterior condylar axis and Whiteside’s anteroposterior line. Then we measured the angles among these lines and analyzed the data and evaluated the relationship between them. In 82 patients, mean angle between anatomical transepicondylar axis and posterior condylar axis and between surgical transepicondylar axis and posterior condylar axis were 5.68°±1.89 ° and 1.9°±1.85° respectively. Mean angle between Whiteside’s anteroposterior line and posterior condylar axis was 3.89°±1.64°. There were significant differences between the two genders in these relationships. No significant correlation between patients’ age and angles of distal femur was detected. There was a good correlation between anatomical and surgical axes situations, as anatomical transepicondylar axis was in 3.78° externally rotation related to surgical transepicondylar axis. Preoperative CT scan can help to determine rotational landmarks of distal femur more accurately. If one of the reference axes could not be determined, we can use other reference axes because of good correlations between these landmarks.