<prompt> Please answer with one of the option in the bracket. Write reasoning in between . Write answer in between .Q:A 51-year-old woman comes to the emergency department because of a 1-day history of severe pain in her left knee. To lose weight, she recently started jogging for 30 minutes a few times per week. She has type 2 diabetes mellitus and hypertension treated with metformin and chlorothiazide. Her sister has rheumatoid arthritis. She is sexually active with two partners and uses condoms inconsistently. On examination, her temperature is 38.5C 101.3F, pulse is 88min, and blood pressure is 13887 mm Hg. The left knee is swollen and tender to palpation with a significantly impaired range of motion. A 1.5-cm, painless ulcer is seen on the plantar surface of the left foot. Which of the following is most likely to help establish the diagnosis?? A: Perform MRI of the knee, B: Perform arthrocentesis, C: Measure HLA-B27, D: Measure rheumatoid factor, E: Perform ultrasonography of the knee,  <response>: This is a clinical vignette describing a 51-year-old woman with new onset left knee pain and swelling. She has several risk factors including obesity, type 2 diabetes, hypertension, and inconsistent condom use suggesting possible sexually transmitted infections. On exam she has a fever, left knee swelling and tenderness, and decreased range of motion. She also has a painless left plantar ulcer suggesting possible diabetic neuropathy. The key finding is an acute monoarticular arthritis of the left knee in a patient with systemic symptoms fever. The differential diagnosis includes septic arthritis, gout, and reactive arthritis. Imaging such as MRI could show effusion but would not help make the diagnosis. Measuring rheumatoid factor or HLA-B27 would not be helpful as this presentation is not consistent with rheumatoid arthritis or ankylosing spondylitis. Performing arthrocentesis to analyze the synovial fluid would allow assessment of the white blood cell count, culture, and crystals to help distinguish between septic arthritis, gout, and reactive arthritis. Ultrasonography could detect effusion but would not provide additional diagnostic information.B: Perform arthrocentesis 