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: Anatomy
Physiological unlocking is caused by - 
Select and explain. 
A. Popliteus, B. Rectus femoris, C. Semimembranosus, D. Sartorius
A: Popliteus
Answer: A: Popliteus 
Explanation: During last stages of extension, femur rotates medially on tibia due to quadriceps femoris to lock the knee joint. Femur rotates laterally on tibia during flexion. 
Quadriceps femoris- Vastus medialis, vastus lateralis, vastus intermedius, rectus femoris. Unlocking occurs with popliteus.