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Septic Arthritis — RACP Adult Medicine MCQ

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ModerateGeneral Internal MedicineSeptic ArthritisRACP Adult Medicine

A 68-year-old woman with rheumatoid arthritis on methotrexate and prednisolone 7.5 mg daily develops a painful, hot, swollen knee. Synovial fluid aspirate shows WCC 85,000 cells/µL (95% neutrophils). No crystals are seen. Gram stain shows Gram-positive cocci in clusters. What is the most appropriate management?

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Correct answer: C — IV flucloxacillin and arthroscopic washout

Septic arthritis (confirmed by high WCC with Gram-positive cocci – likely S. aureus) in an immunosuppressed patient requires urgent IV antibiotics (flucloxacillin for MSSA; vancomycin if MRSA risk) AND joint drainage (arthroscopic washout or serial aspiration). Delay in treatment leads to irreversible joint destruction. Methotrexate should be withheld during active sepsis.

Reference: eTG – 2025 – Antibiotic Guidelines; BSR – 2006 – Septic Arthritis Guidelines