Both collateral ligaments resist what motion of the tibia?

• A. Medial rotation
• B. Lateral rotation
• C. Anterior translation
• D. Posterior translation

Answer: (A)

Collateral ligaments stabilize the knee not only against side-to-side (valgus/varus) forces but also against twisting of the tibia relative to the femur. When the tibia attempts to rotate medially, the fibers of both the medial and lateral collateral ligaments become taut, providing resistance and helping keep the knee stable. This rotational restraint is why medial rotation is the motion they best resist. By contrast, anterior and posterior translation are primarily controlled by the cruciate ligaments, so those motions are not what the collateral ligaments specialize in resisting.