Joint Fluid Analysis

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    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
        gout.JPG pseudogout.jpg

     

     

    • 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

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