Osteoarthritis Quiz: Ace Your Exams

An 82-year-old woman presents to the office for evaluation of intermittent bilateral hand pain for the past few years. She describes the pain as dull and aching. It worsens when she does activities such as crocheting, knitting, or gardening and improves with rest. She has stiffness in the morning that lasts 15 minutes. She has a history of hypertension for which she takes amlodipine. She has been massaging her hands and using over-the-counter topical ointments to manage the pain. Temperature is 36.9°C (98.4°F), pulse is 80/minute, respiratory rate is 16/minute, blood pressure is 128/76 mmHg, and BMI is 26 kg/m². An image of her hands is shown below. On physical examination there is tenderness to palpation of multiple DIP and PIP joints bilaterally with bony enlargement without boggy swelling or warmth. Which of the following should be done next to confirm the diagnosis?
 
^{Image reproduced from Wikimedia Commons}