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Septic arthritis — MCCQE Part 1 MCQ

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HardJoint PainSeptic arthritisMCCQE Part 1

A 61-year-old man with diabetes presents with acute hot swollen right knee and fever. He cannot bear weight. Synovial fluid is cloudy with WBC 85,000/mm3 and Gram-positive cocci seen. What is the most likely diagnosis?

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Correct answer: B — Septic arthritis

Fever, inability to bear weight, very high synovial WBC, and organisms on Gram stain indicate septic arthritis. Gout and pseudogout can produce acute monoarthritis but Gram-positive cocci make infection the best answer. Prepatellar bursitis is more superficial and extra-articular. Osteoarthritis flares are not associated with purulent synovial fluid.

Reference: Canadian rheumatology and infectious disease guidance