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Approach to acute joint pain

The same eight steps, every presentation: threats first, then the history and exam that discriminate, one honest sentence, a mechanism-grouped differential, and the tests read in order.

  1. Immediate threats

    • Septic arthritis: the hot joint that destroys cartilage in days
    • The prosthetic joint infection
    • Fracture and hemarthrosis on anticoagulation

  2. History that discriminates

    • One joint or many; first attack or a known pattern
    • Tempo: hours (crystals, sepsis) versus weeks (inflammatory arthritis)
    • Morning stiffness beyond an hour points inflammatory
    • Gout risks: diuretics, alcohol, chronic kidney disease, prior podagra

  3. Examination

    • The four signs of true arthritis versus periarticular pain: effusion, warmth, tenderness, loss of range
    • Pattern across joints: symmetric small (RA-like) versus asymmetric large
    • Skin: psoriasis, tophi, purpura
    • Fever means tap, whatever else is true

  4. Problem representation

    An abruptly hot, exquisitely tender first MTP in a man on diuretics (gout) versus a hot knee with fever and inability to weight-bear (septic until the tap says otherwise).

  5. Differential, by mechanism

    Monoarthritis

    • Septic arthritis
    • Gout
    • Pseudogout
    • Trauma/hemarthrosis

    Oligo/polyarthritis

    • Rheumatoid
    • Psoriatic
    • Reactive
    • Viral
    • Lupus

    Periarticular mimics

    • Bursitis
    • Tendinopathy
    • Cellulitis

  6. Investigations

    • Aspirate the acute monoarthritis: cell count, Gram stain, culture, crystals
    • Crystals do not exclude infection; the two coexist
    • Uric acid can be normal in an acute gout attack
    • Inflammatory markers trend, not diagnose

  7. Interpretation

    • Synovial WBC climbs through inflammatory (2k-50k) toward septic (>50k) territory, but overlap is real
    • Negatively birefringent needles are gout; rhomboid positive crystals are pseudogout

  8. Next steps

    • The septic joint gets drainage and IV antibiotics the same day
    • Gout treatment chooses among NSAID, colchicine, steroid by the patient's kidneys and comorbidities

Connected

FluidThe hot joint, tappedFluidCrystals under the scopeScriptGout illness script

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