Which action describes the popliteus?

Which action describes the popliteus?

• A. Weakly Flexes Knee
• B. Medially Rotates Tibia While Non-Weight Bearing
• C. Unlocks Knee by Laterally Rotating Femur 5 Degrees on Tibia
• D. Does Not Affect Knee Rotation

Answer: (C)

The popliteus’s main role is to unlock the knee from its fully extended, “locked” position to start flexion. It does this by creating a small rotation between the femur and tibia. Specifically, contraction of the popliteus produces about 5 degrees of lateral rotation of the femur on the tibia (equivalently, a slight medial rotation of the tibia relative to the femur when described from the opposite perspective). This slight rotation breaks the screw-home mechanism that locks the knee in full extension and allows the knee to begin flexion. Anatomically, the muscle runs from the lateral femoral condyle to the posterior tibia, so its pulling action directly translates into this rotation, rather than into mere knee bending. That’s why describing the popliteus as “unlocking the knee by laterally rotating the femur on the tibia” best captures its essential action.

The popliteus’s main role is to unlock the knee from its fully extended, “locked” position to start flexion. It does this by creating a small rotation between the femur and tibia. Specifically, contraction of the popliteus produces about 5 degrees of lateral rotation of the femur on the tibia (equivalently, a slight medial rotation of the tibia relative to the femur when described from the opposite perspective). This slight rotation breaks the screw-home mechanism that locks the knee in full extension and allows the knee to begin flexion.

Anatomically, the muscle runs from the lateral femoral condyle to the posterior tibia, so its pulling action directly translates into this rotation, rather than into mere knee bending. That’s why describing the popliteus as “unlocking the knee by laterally rotating the femur on the tibia” best captures its essential action.