Joint Fluid Analysis

Synovial Fluid Analysis

• Consists of plasma (ultrafiltrate) + hyaluronic acid that lubricates joint  
• Absolute Indication!:
  • Acute inflammatory monoarthritis that is not traumatic!!
 
• Contraindications:
  • Absolute:
    • Open lesion
    • Suspected infection of overlying skin
  • Relative
    • Bleeding diathesis
    • Thrombocytopenia
    • Prosthetic joint
• Synovial Fluid Examination:
  • Cell count & Differential (bacteria, fungi, Lyme)
  • Culture & Gram Stain
  • Crystals (Microscopy with polarized light)
    • Gout (Monosodium Urate) -->
      • Needle-shaped
      • Negatively birefringent (yellow parallel to polarization, blue when perpendicular)
      • During acute attack see them being phagocytosed in macrophages (intracellular)
    • Pseudogout (Calcium pyrophosphate dihydrate) --> r
      • Rhomboid-shaped
      • Positively birefringent (very weak birefringent, not as bright/pretty, and blue when parallel to polarizer)
  • NOTE: Seeing crystals on joint fluid aspiration does not rule out infection --> must cover with antibiotics (i.e. Vanco+ceftriaxone) and await culture!

  • Gout	Pseudogout

• General Principle:
  • Synovial leukocyte count:
    • < 2,000 -- Non-inflammatory
    • 2,000 - 50,000 - Likely inflammatory, can be infectious as well (does not rule out infection!!)
    • > 50,000 - Very likely infectious
  • PMNs
    • < 25% -- Non-inflammatory
    • >50% -- Inflammatory
    • > 75% -- Likely infectious.

• Parameter	Normal	Non-Inflammatory	Infammatory	Infectious	Hemorrhagic
  Colour	Pale Yellow	Pale Yellow	Pale Yellow	Yellow-White	Red/Browth
  Clarity	Clear	Clear	Opaque	Opaque	Sanguinous
  Viscocity	High	High	Low	Low	Variable
  WBC/mm3	<200	<2,000	>2,000	>50,000	Variable
  %PMN	<25%	<25%	>25%	>50%	Variable
  Culture/Gram				POSITIVE
  Examples		Trauma Osteoarthritis	Seropositives Seronegatives Crystal   Arthropathies	S. aureus Gram neg. Gonococcal  (hard to cult)	Trauma Hemophilia