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
Locking of knee joint occurs due to - 
Select and explain. 
A. Lateral rotation of femur during last degrees of extension., B. Medial rotation of femur during last degrees of extension, C. Lateral rotation of femur during last degrees of flexion, D. Medial rotation of femur during last degrees of flexion
B: Medial rotation of femur during last degrees of extension
Answer: B: Medial rotation of femur during last degrees of extension 
Explanation: During last stages of extension, femur rotates medially on tibia due to quadriceps femoris to lock the knee joint.