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
[{'content': 'A 18 yrs old boy was playing football, when he suddenly twisted his knee on the ankle and he fell down. He got up after 10 minutes and again staed playing, but next day his knee was swollen and he could not move it. The most probable cause is: \nSelect and explain. \nA. Medial meniscus tear, B. Anterior cruciate ligament tear, C. Medial collateral ligament injury, D. Posterior cruciate ligament injury', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Injury to the medial meniscus is the most frequent internal derangement of the knee joint. Clinical findings include swelling, pain, and varying degrees of restriction of flexion or extension. True locking (inability to fully extend the knee) is highly suggestive of meniscal tear. A marginal tear permits displacement of the medial fragment into the intercondylar region (bucket-handle tear) and prevents either complete extension or complete flexion. Ref: Srinivasan R.C., Tolhurst S., Vanderhave K.L. (2010). Chapter 40. Ohopedic Surgery. In G.M. Dohey (Ed), CURRENT Diagnosis & Treatment: Surgery, 13e.', 'role': 'assistant'}]