This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Lower limb, Subject name: Anatomy
Physiological unlocking is caused by 
Select and explain. 
A. Popliteus, B. Rectus femoris, C. Semi-membranous, D. Saorius
A: Popliteus
Answer: A: Popliteus 
Explanation: Locking is produced by continued action of the same muscles that produce extension, i.e. the quadriceps femoris (the vastus lateralis, vastus medialis , vastus intermedius and the rectus femoris ). The locked knee joint can be flexed only after it is unlocked i.e., by lateral rotation of the femur. Unlocking is brought about by the action of the popliteus muscle. Ref : B D Chaurasia's Human Anatomy , seventh edition , volume 2, pg. no. 157