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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 59-year-old man presents to general practice 5 days after falling directly onto his right knee while gardening. He sustained a small superficial abrasion over the patella but was able to walk home and had only mild pain initially. Over the last 18 hours, he has developed rapidly worsening knee pain and swelling and is now unable to weight-bear. He has type 2 diabetes and polymyalgia rheumatica treated with prednisolone 10 mg daily. He looks unwell. His temperature is 38.3°C, pulse 104 beats/minute and blood pressure 132/76 mmHg. The knee has a diffuse tense effusion and is warm, with marked pain on both active and passive movement. There is no focal fluctuant swelling confined to the prepatellar bursa, no deformity and no distal neurovascular deficit. What is the most appropriate management today?

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Correct answer: C — Arrange emergency hospital assessment for suspected septic arthritis of the knee

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

This is suspected septic arthritis requiring emergency hospital assessment. The key discriminator is not the preceding trauma alone, but the change in trajectory: initially mild symptoms with preserved walking, followed several days later by rapidly progressive severe monoarthritis, a tense effusion, fever, systemic upset and marked pain on passive movement. Diabetes and regular prednisolone further increase concern because immunosuppression predisposes to joint infection. A superficial abrasion also provides a potential route for bacterial inoculation. B is inappropriate because an outpatient pathway risks delaying joint aspiration, drainage and intravenous antibiotics. C may be reasonable only for a clinically well, afebrile patient when septic arthritis is less likely and an appropriately skilled clinician can aspirate promptly; it is not appropriate in this febrile, immunosuppressed patient. D is tempting because of the anterior abrasion, but prepatellar bursitis usually causes more localised superficial swelling and does not usually cause such severe pain on passive movement of the knee joint. E fails because traumatic synovitis should begin immediately after injury and should not produce fever and systemic illness several days later.

Reference: NHS: Septic arthritis (Last reviewed 23 March 2023) — https://www.nhs.uk/conditions/septic-arthritis/ NHS Borders Ref Help Toolkit: Rheumatology and bone disease (Accessed 15 August 2026) — https://www.rightdecisions.scot.nhs.uk/borders-ref-help-toolkit/rheumatology-and-bone-disease/rheumatology-and-bone-disease/