Review Question - QID 210956

A 30-year-old woman presents to the emergency room for evaluation of a swollen, painful knee. She says the pain began approximately 2 months ago and has progressively worsened, and rest, ibuprofen, and aspirin have brought no relief. She denies any trauma to the site. BMI is 23 kg/m^2 and she is not very physically active. Her temperature is 98.7°F (37.1°C), blood pressure is 110/71 mmHg, pulse is 60/min, respirations are 12/min, and oxygen saturation is 98% on room air. On exam, you note mild edema and decreased range of motion. Lab values, including serum electrolytes and parathyroid hormone levels, are within normal limits. A radiograph of the knee is shown in Figure A. Which of the following is the most likely diagnosis?