Review Question - QID 109793

A 45-year-old man with a body mass index of 45 kg/m^2 presents to his primary care doctor with right knee pain. The pain is instigated by walking up and down stairs around a construction site which he oversees. He has no significant medical history. His temperature is 98.6°F (37°C), blood pressure is 118/74 mmHg, pulse is 82/min, and respirations are 12/min. On physical exam, his hips are symmetric and equal with no tenderness to palpation bilaterally. His left lower extremity appears grossly normal with full range of motion. His right knee appears symmetric, but the patient has tenderness when the anteromedial part of the tibial plateau is pressed. No other parts of his knee are tender. No tenderness is elicited with extension, flexion, varus, and valgus movements of the knee. McMurray test is negative with both internal and external rotation of the right leg. Which of the following is the most likely diagnosis?