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Septic arthritis of the native knee — RCPSC EM MCQ

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ModerateMusculoskeletalSeptic arthritis of the native kneeRCPSC EM

CTAS 3: A 58-year-old with diabetes presents with an acutely painful swollen knee and fever. Vitals are T 38.5°C, HR 108, BP 132/78. The knee is warm with severe pain on passive motion and no overlying cellulitis. Serum WBC and CRP are elevated. What is the most appropriate investigation?

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Correct answer: A — Urgent arthrocentesis for synovial fluid analysis and culture

A hot painful joint with systemic features is septic arthritis until proven otherwise. Synovial WBC, Gram stain, culture and crystal analysis guide management; antibiotics follow cultures when feasible.

Reference: IDSA septic arthritis principles; Royal College EM Objectives