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Synovial fluid interpretation — SCE Rheumatology MCQ

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HardMusculoskeletal InvestigationsSynovial fluid interpretationSCE Rheumatology

A febrile patient has an acutely swollen knee. Synovial fluid contains calcium-pyrophosphate crystals and 58,000 leucocytes/mm³; Gram stain is negative, but blood cultures grow Staphylococcus aureus. What is the next management principle?

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Correct answer: B — Drain the joint and treat septic arthritis despite the CPP crystals

The best answer is “Drain the joint and treat septic arthritis despite the CPP crystals”. Crystals do not exclude septic arthritis; the positive blood cultures and acutely inflamed joint require urgent drainage and antimicrobial treatment. Awaiting synovial culture delays source control, treating bacteraemia alone is inadequate, and intra-articular glucocorticoid is unsafe in suspected infection.

Reference: European guideline for septic arthritis in native joints: https://jbji.copernicus.org/articles/8/29/2023/