Which structure increases the moment arm of the knee extensor muscles?

Which structure increases the moment arm of the knee extensor muscles?

• A. Proximal tibiofibular joint
• B. Tibiofemoral joint
• C. Patellofemoral joint
• D. Menisci

Answer: (C)

The key idea is how the lever arm of the knee extensors is altered. The patella, sitting in the patellofemoral joint, acts like a pulley that redirects the force of the quadriceps tendon. By placing the tendon’s line of pull further anterior to the knee’s axis of rotation, it increases the perpendicular distance from the axis to the force. That bigger moment arm means for the same muscle force, you generate more knee extension torque. This mechanical advantage is most noticeable as the knee bends through mid-range angles. The other structures don’t change this lever arm. The proximal tibiofibular joint is not part of the knee’s extensor mechanism; the tibiofemoral joint is the hinge where movement occurs but doesn’t by itself increase the moment arm; the menisci mainly improve joint stability, congruence, and load distribution.

The key idea is how the lever arm of the knee extensors is altered. The patella, sitting in the patellofemoral joint, acts like a pulley that redirects the force of the quadriceps tendon. By placing the tendon’s line of pull further anterior to the knee’s axis of rotation, it increases the perpendicular distance from the axis to the force. That bigger moment arm means for the same muscle force, you generate more knee extension torque. This mechanical advantage is most noticeable as the knee bends through mid-range angles.

The other structures don’t change this lever arm. The proximal tibiofibular joint is not part of the knee’s extensor mechanism; the tibiofemoral joint is the hinge where movement occurs but doesn’t by itself increase the moment arm; the menisci mainly improve joint stability, congruence, and load distribution.