Q. A police officer, aged 29, comes to your clinic with left knee pain, swelling, and joint instability. Two weeks ago, he had a contact injury in a football game, which resulted in immediate knee swelling and severe pain. He was not able to continue the game. The initial x-ray following the injury did not show any fractures. He was treated with a knee brace, cold pack, protected weight bearing (using a crutch), an analgesic, and a recommendation to visit a physician after two weeks. Now, he has pain in knee motion, but not while bearing weight. He has no significant medical history. The left knee has slight effusion, tenderness on the medial joint line, and slight quadriceps atrophy. The joint is not warm, and there is no erythema around the joint. The valgus and varus stress tests are negative, but the anterior drawer, Lachman, and McMurray tests are positive. What is the best diagnostic method for him?