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Suspected septic arthritis of the native knee after minor trauma — MSRA MCQ

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HardKnee InjuriesSuspected septic arthritis of the native knee after minor traumaMSRA

A 58-year-old man presents to a GP-led urgent treatment centre 6 days after twisting his right knee while stepping off a kerb. He had mild pain initially and remained able to walk. Over the past 18 hours, however, the knee has become rapidly more painful, swollen and hot. He now cannot weight-bear. He has previously had podagra and takes allopurinol. He has type 2 diabetes. His temperature is 38.2°C, pulse 96 beats/minute, blood pressure 132/76 mmHg and NEWS2 is 2. The knee has a tense effusion, diffuse warmth and marked pain throughout passive flexion and extension. There is no focal bony tenderness, ligamentous laxity or overlying cellulitis. A small superficial abrasion from the original fall is dry and healing. Plain radiographs show no fracture. CRP is 156 mg/L and serum urate is 0.49 mmol/L. What is the most appropriate management today?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — Arrange immediate hospital assessment for blood cultures and urgent knee aspiration before antimicrobial treatment, with orthopaedic discussion

Explanation lettering: B = shown as A · E = shown as B · A = shown as C · C = shown as D · D = shown as E

This is suspected septic arthritis until proved otherwise. The initial twisting injury may have been minor, but the decisive features are rapid clinical deterioration, fever, inability to weight-bear, a tense hot effusion and severe restriction of passive as well as active movement. Diabetes further increases concern for infection. A raised serum urate and previous podagra do not establish gout and must not be used to exclude septic arthritis. Immediate hospital assessment is required for prompt blood cultures, diagnostic joint aspiration (including microscopy/crystal analysis and culture), and orthopaedic involvement because drainage or washout may be required. In this haemodynamically stable patient, appropriate microbiological samples should be obtained before antibiotics where this does not delay necessary treatment. A is plausible because gout commonly affects the knee and the urate is elevated, but treating presumptively risks missing a joint-threatening infection. C gives antibiotics before obtaining diagnostic samples and inappropriately substitutes oral community treatment for urgent assessment and source control. D addresses structural injury, but MRI would delay management of a suspected infected joint. E is inappropriate because intra-articular corticosteroid should not be given when septic arthritis remains possible.

Reference: Gout: diagnosis and management (NG219), Recommendations (2022) — https://www.nice.org.uk/guidance/ng219/chapter/Recommendations Septic Arthritis / Osteomyelitis (Native joint, not diabetic ulcer associated) (Reviewed 1 February 2026) — https://www.rightdecisions.scot.nhs.uk/antimicrobial-prescribing-nhs-borders/adult-hospital-guidance/musculoskeletal-and-joint/septic-arthritis-osteomyelitis-native-joint-not-diabetic-ulcer-associated/ Acute Monoarthritis (Reviewed 1 May 2025) — https://www.rightdecisions.scot.nhs.uk/nhs-tayside-refguide/medicine/rheumatology/acute-monoarthritis/