Review Question - QID 217007

A 22-year-old college football player presents to the team trainer with right knee pain after football practice. He has been able to bear weight on the affected extremity but feels more comfortable using crutches. He denies fevers, chills, or prior injury to the affected extremity. He has no other medical problems and takes no medications. He drinks 5-6 beers a week and plays the running back position. His temperature is 99.9°F (37.7°C), blood pressure is 124/72 mmHg, pulse is 68/min, and respirations are 16/min. Physical exam reveals a healthy-appearing man with mild swelling of the right knee and medial joint line tenderness. The pain is worsened with knee extension. When he is asked to stand on his right leg with the knee flexed to 20 degrees and to twist, he experiences discomfort in the knee. Which of the following is the most likely diagnosis in this patient?