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Arthrocentesis Quick Look

Tina Arkee

Indications for arthrocentesis:

  • Monoarthritis (acute or chronic)
  • Suspicion for infection, crystal arthropathy, or hemarthrosis
  • Trauma with joint effusion
  • When diagnosis is unclear despite history and other workup

Relative Contraindications to arthrocentesis

  • Extensive cellulitis or psoriatic plaque around the site of interest (risk of introducing bacteria into a sterile space)
  • Coagulopathy
  • Bacteremia
  • Concern for infection of a prosthetic joint – these should only be tapped by Ortho!

What to order

  • Synovial fluid exam (includes cell count and crystal exam). *Note: may see similar cell counts in gout and septic arthritis. The presence of crystals does not necessarily rule out septic arthritis.
  • Body fluid gram stain and culture

Synovial Fluid Analysis

Non-inflammatory Inflammatory Septic Hemorrhagic
Appearance Clear straw/yellow Clear to cloudy yellow Opaque/turbid yellow green Reddish brown
Cell count <2000 >2000–50,000 >50,000 <2000
% of PMNs <25% >50% >75% <50%
Culture Negative Negative Positive Negative
Crystals No Yes
Gout: needle shaped, negatively birefringent
Pseudogout: rhomboid shaped, positively birefringent
No No
DDx Osteoarthritis, trauma, osteonecrosis Inflammatory arthritis, crystal arthritis, sarcoidosis, indolent infections Septic arthritis Trauma, coagulopathy


  • Monosodium urate: needle-shaped, negatively birefringent
    • Sensitivity is generally good (>90s%)
  • Calcium pyrophosphate dihydrate: rhomboid-shaped, positively birefringent (weakly), appear blue when parallel to the polarizer
    • Weak birefringence significantly reduces sensitivity