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Septic arthritis — MCCQE Part 1 MCQ

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HardJoint PainSeptic arthritisMCCQE Part 1

A 63-year-old man with rheumatoid arthritis on prednisone presents with acute swollen painful right knee and fever. He cannot bear weight, white blood cell count is 16 × 10^9/L, and x-ray shows no fracture. What is the most appropriate investigation?

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Correct answer: C — Urgent arthrocentesis for synovial fluid Gram stain, culture and crystal analysis

An acutely hot swollen joint with fever in an immunosuppressed patient is septic arthritis until proven otherwise; urgent arthrocentesis is required before or alongside antibiotics when feasible. Serum uric acid cannot exclude infection. Crystal disease and infection can coexist, so synovial analysis should include both culture and crystals.

Reference: Canadian Rheumatology Association Choosing Wisely