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: Orthopaedics
[{'content': 'When a patient gets up from sitting position which of the following events takes place in his knee joint? \nSelect and explain. \nA. Medial rotation of femur on a fixed tibia, B. Lateral rotation of femur on a fixed tibia, C. Medial rotation of tibia on a fixed femur, D. Lateral rotation of tibia on a fixed femur', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Physiological locking occurs in extension when the femur is internally (medially) rotated on a fixed tibia.\nLocking is a mechanism that allows the knee to remain in the position of full extension as in standing without much muscular efforts and is caused by quadriceps femoris.', 'role': 'assistant'}]