Which is an action of the popliteus?

• A. Medially rotate the flexed knee
• B. Laterally rotate the extended knee
• C. Extend the knee
• D. Flex the hip

Answer: (A)

The popliteus’s job is to unlock the knee by rotating the tibia medially relative to the femur, which allows the knee to begin flexing from a straight position. In practical terms, when the knee starts to flex from full extension, the popliteus contracts to rotate the tibia inward, enabling movement. That’s why the action described as medially rotating the flexed knee best fits what the muscle does. The other options involve actions of different muscles or directions that aren’t typical of the popliteus—extending the knee is done by the quadriceps, hip flexion by hip muscles, and laterally rotating an extended knee isn’t the popliteus’s function.