Monoarticular Disease

Atraumatic monotraumatic joint pain

  • Inflammatory – can be caused by
    – microcrystals (gout & pseudogout)
    – microorganisms (septic arthritis)
    – autoinflammatory (RA)
    – reactive arthritis
    – spondyloarthritis
  • Mechanical OA

Epidemiology

  • Inflammatory monoarthritis affects men > women (because gout is more common in men)
  • Most common joint -> Knee
  • Crystal arthritis is the most common diagnosis followed by reactive arthritis, RA Septic arthritis.
  • Most important diagnosis to exclude is septic arthritis. Risk factors are RA, OA, Prosthetic joints, low socioeconomic status, IV drug abuse, alcoholism, diabetes, previous intra-articular CSI, HIV, cutaneous ulcers. Most common organism is staph aureus followed by staph pyogenes.
  • Redness over skin is highly suggestive of either crystal arthritis or septic arthritis.

Onset

  • Gout & Pseudogout – acute onset (usually over hours to days).
  • Septic arthritis – 1-2 weeks.

Investigations

  • For acute non traumatic inflammatory monoarthritis
    – plain radiograph
    – arthrocentesis / synovial fluid analysis (this also excluded septic arthritis)
  • Lab tests
    – FBC (to assess total white cell count and neutrophil count). Total white cell count can be normal in initial presentation in septic arthritis. CRP is a more reliable predictor in this context.
    – CRP, ESR
    – Liver function (important in management decisions)
    – blood culture (in suspected septic arthritis) before initiation of antibiotic therapy.
    – serum uric acid levels. These fall during an acute systemic inflammatory response. So they are not helpful to exclude gout if they are low.
    – Arthrocentesis. Joint fluid analysis, gram staining and culture.
    – Polarised Light Microscopy – demonstration of microcrystals in synovial fluid is gold standard for crystal arthritis.
  • Radiology – X-ray, MRI
    – helpful to diagnose AVN, heamochromatosis, PVNS
  • Supplementary Investigations
    – arthroscopic biopsy of synovium in case it persists beyond several weeks.

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