This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Physiological locking involves 
Select and explain. 
A. Internal rotation of femur over stabilized tibia, B. Internal rotation of tibia over stabilized femur, C. External rotation of tibia over stabilized femur, D. External rotation of femur over stabilized tibia
A: Internal rotation of femur over stabilized tibia
Answer: A: Internal rotation of femur over stabilized tibia 
Explanation: A i.e. Internal rotation of femur over stabilized tibia Physiological locking occurs in last 30 degree of extension, when femur rotates medially (internally) over stabilized tibiaQ. This very stable position is caused by quadriceps femoris muscle. Unlocking needed to initiate flexion is carried out by popliteus muscle, which moves femur laterally on stabilized tibia.