Which of the following is NOT a reference line used to define the femur axis?

• A. Posterior Condylar Axis
• B. TransEpicondylar Axis
• C. AP Axis/Whiteside's Line
• D. Medial Malleolus Line

Answer: (D)

Defining the femoral axis relies on reference lines on the femur itself to guide rotational alignment during knee procedures. The posterior condylar axis is a line along the back of the femoral condyles and is commonly used to set how the femur is rotated. The transepicondylar axis runs between the medial and lateral epicondyles and serves as another anatomical reference for femoral rotation. Whiteside’s line, the anteroposterior axis, uses the deepest point of the trochlear groove on the front of the femur to help orient the femoral component. The line through the medial malleolus, however, is a tibial/ankle landmark and does not define the femur’s axis. Because it doesn’t pertain to the femur’s rotational reference, it’s the one that does not belong as a femoral-axis reference line.