Joint, bone & spine infection flashcards
13 high-yield MRCP Part 1 cards from the Intellect Medicos Rheumatology course. Try to answer each question before you open it — then study them properly with spaced repetition, which brings each card back just before you would forget it.
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What is the most common organism causing septic arthritis overall?
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Staphylococcus aureus.
Why? In sexually active young adults, Neisseria gonorrhoeae is the classic cause.
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What is the key first-line investigation in a suspected septic joint?
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Urgent joint aspiration for Gram stain, culture and cell count — before antibiotics (plus blood cultures).
Why? Aspirating first maximises the chance of identifying the organism; then start empirical antibiotics immediately.
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In septic arthritis the synovial fluid white cell count is usually above ______ cells per microlitre.
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50,000
Why? Counts this high are typical of bacterial infection, although crystal arthritis can occasionally overlap.
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What is the empirical antibiotic for native-joint septic arthritis, and the alternative in penicillin allergy?
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Flucloxacillin; clindamycin if penicillin-allergic.
Why? Empirical therapy covers Staph aureus and streptococci, then is tailored to culture.
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A 22-year-old woman has fever, migratory polyarthralgia, tenosynovitis of the wrist and a few pustular skin lesions, then develops a hot swollen knee. What is the treatment of disseminated gonococcal infection?
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Ceftriaxone 1 g IV (or IM) once daily, for 7 days in total.
Why? N. gonorrhoeae is the classic cause of septic arthritis in sexually active young adults. BASHH allows an oral switch (e.g. cefixime) 24–48 hours after improvement.
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Which organism group is classically associated with infection of prosthetic joints and other implanted material?
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Coagulase-negative staphylococci (e.g. Staph epidermidis).
Why? They form biofilms on foreign material. Staph aureus is also common.
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What is the imaging modality of choice for osteomyelitis?
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MRI.
Why? Plain X-ray is the first image but may be normal for the first 2 weeks or so; MRI shows marrow oedema early.
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What is the gold-standard (definitive) diagnostic test for osteomyelitis?
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Bone biopsy for culture and histology.
Why? It confirms infection and gives the organism and sensitivities, which guides weeks of antibiotics.
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Which organism is classically associated with osteomyelitis in sickle cell disease?
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Salmonella.
Why? Bowel infarction lets gut organisms reach infarcted bone.
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What is the standard antibiotic treatment for staphylococcal osteomyelitis (no penicillin allergy)?
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Flucloxacillin for about 6 weeks (starting IV); clindamycin if penicillin-allergic.
Why? Bone penetration is poor and infection is deep-seated, so prolonged treatment is needed.
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A 62-year-old man with diabetes who injects drugs has 3 weeks of severe, constant thoracolumbar back pain with spinal tenderness. He is afebrile; CRP is 140 mg/L. What is the gold-standard imaging investigation?
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MRI of the whole spine.
Why? Discitis/spondylodiscitis is usually haematogenous Staph aureus; fever is often absent, and MRI also shows epidural abscess.
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What is the gold-standard investigation for an iliopsoas abscess?
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CT of the abdomen (and pelvis).
Why? Patients present with fever, flank/back pain and a limp, and hold the hip flexed because extension stretches the psoas.
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What is the first-line definitive management of an iliopsoas abscess?
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CT-guided percutaneous drainage plus antibiotics (e.g. IV flucloxacillin ± gentamicin).
Why? Surgery is used if drainage fails. Secondary abscesses from a GI source (e.g. Crohn's) need broader cover such as piperacillin–tazobactam.