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Staphylococcus aureus septic arthritis of a native joint — SCE Rheumatology MCQ

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ModerateSeptic ArthritisStaphylococcus aureus septic arthritis of a native jointSCE Rheumatology

A 67-year-old woman with seropositive rheumatoid arthritis treated with methotrexate presents with a 3-day history of fever and a painful, swollen native left wrist. Before admission, she received two doses of oral co-amoxiclav for presumed cellulitis. Synovial aspiration yields purulent fluid, and she undergoes surgical washout. Synovial fluid culture grows methicillin-susceptible Staphylococcus aureus; three sets of blood cultures remain negative. She is commenced on intravenous flucloxacillin following microbiology review. She is now haemodynamically stable and has no cardiac murmur, peripheral stigmata of infective endocarditis, spinal pain, focal neurological symptoms or other localising features. Her wrist pain and inflammatory markers are improving after drainage. Which additional imaging investigation is most appropriate?

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Correct answer: D — Transthoracic echocardiography

The organism is the decisive discriminator. Cardiac imaging is recommended in native-joint septic arthritis caused by Staphylococcus aureus because infective endocarditis may be clinically occult. Negative blood cultures do not remove this indication here: antimicrobial exposure preceded culture collection and may have reduced microbiological sensitivity. Transthoracic echocardiography is the appropriate initial cardiac imaging investigation; further imaging, including transoesophageal echocardiography, would depend on its findings and the subsequent clinical assessment. Whole-spine MRI would be appropriate if there were spinal pain, neurological findings or other evidence suggesting vertebral osteomyelitis or epidural infection. CT of the chest, abdomen and pelvis is not routinely required when a drained joint is responding and there are no symptoms indicating another deep focus. FDG PET-CT may help investigate persistent unexplained infection, suspected metastatic foci or infected prosthetic material, but is disproportionate as the initial investigation in this improving patient. MRI of the wrist may define adjacent osteomyelitis or a residual deep collection when the clinical response is unsatisfactory; it does not replace organism-directed screening for endocarditis. The absence of a murmur or peripheral stigmata is insufficient to exclude infective endocarditis.

Reference: 2020 French recommendations on the management of septic arthritis in an adult native joint (2020) — https://pubmed.ncbi.nlm.nih.gov/32758534/ Management of septic arthritis in adults with a hot swollen joint: British Society for Rheumatology guideline scope (16 June 2025) — https://pubmed.ncbi.nlm.nih.gov/40524816/