How is the mechanical axis of the leg defined?

How is the mechanical axis of the leg defined?

• A. Center of the femoral head to the center of the tibial head at the talus
• B. Center of the femoral head to the center of the ankle
• C. Center of the pelvis to the ankle
• D. Center of the femoral head to the center of the tibial head at the talus

Answer: (D)

The mechanical axis of the leg is the straight weight-bearing line that runs from the center of the femoral head to the center of the ankle joint (the talus). This line passes through the knee and shows how load is transmitted through the leg when standing. It’s why radiographs draw a line from the femoral head center down to the talar dome center: that path represents the actual load path from hip to ankle. The pelvis isn’t part of this axis, and the endpoint isn’t the proximal tibia—the axis ends at the ankle via the talus, defining the true leg alignment.

The mechanical axis of the leg is the straight weight-bearing line that runs from the center of the femoral head to the center of the ankle joint (the talus). This line passes through the knee and shows how load is transmitted through the leg when standing. It’s why radiographs draw a line from the femoral head center down to the talar dome center: that path represents the actual load path from hip to ankle. The pelvis isn’t part of this axis, and the endpoint isn’t the proximal tibia—the axis ends at the ankle via the talus, defining the true leg alignment.