Meniscus tear

A 26-year-old man comes to the office because of severe right knee pain and swelling. The patient currently works as a professional soccer player. His medical history is noncontributory. When asking the patient about his injury, he remembers jumping up to head the ball and colliding with someone in the air to finally land on his right knee. The patient additionally mentions that the pain worsens when he tries to bend his knee and he hears it "click" occasionally. Physical exam shows a "popping sound" on external rotation of his knee, limited knee extension, and tenderness to palpation. His temperature is 36.7°C (97.9°F), pulse is 57/min, respirations are 19/min, blood pressure is 110/60 mmHg. A knee MRI shows a high intrameniscal signal extending to the articular surface.  Which of the following is the most likely diagnosis?