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Synovial Fluid. I. Physiology & Composition Movable joints (diarthroses) composed of: Bones lined with articular cartilage Separated by a cavity containing synovial fluid enclosed in a synovial membrane Synovial membrane synoviocytes: Phagocytic – synthesizes degradative enzymes

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synovial fluid
Synovial Fluid
  • I. Physiology & Composition
    • Movable joints (diarthroses) composed of:
      • Bones lined with articular cartilage
      • Separated by a cavity containing synovial fluid enclosed in a synovial membrane
    • Synovial membrane
      • synoviocytes:
        • Phagocytic – synthesizes degradative enzymes
        • Synthesizes hyaluronate
      • Connective tissue
        • Blood vessels, lymphatics & nerves
    • Fluid formation
      • Ultrafiltrate of plasma across synovial membrane
        • Non selective
        • Excludes proteins of high molecular weight
      • Synoviocytes
        • Secrete mucopolysaccharite which contains:
          • Hyaluronic acid
          • protein
slide2
Cartilage & fluid function:
    • Reduce friction between bones
    • Lubricates joints
    • Fluid provides nutrients to cartilage
    • Lessens shock of walking and jogging impact

Synovial Fluid – Normal Values

Volume <3.5 mL

Color pale yellow

Clarity clear

Viscosity forms string 4-6 cm long

Erythrocytes <2000 cells/uL

Leukocytes <200 cells/uL

Neutrophils <20% of diff.

Lymphocytes <15 % of diff.

Monocytes & macrophages 65% of diff.

Crystals NONE

Glucose <10 mg/dL (lower than blood glucose)

Lactate <250 mg/dL

Total protein <3 g/dL

Uric acid = blood value

slide3
Collection: arthrocentesis – needle aspiration of synovial fluid
    • Volume:
      • Normal= 3.5 mL
      • Diseased / inflamed = up to 25 mL
    • Collect 2 tubes
      • Heparin tube : microbiology
      • Plain top: chemistry and immunology
      • EDTA (liquid) : hematology

*Avoid all powdered anticoagulants – interfere with crystal analysis

    • Fluid verification
      • Mucin clot test-
        • Add fluid to dilute acetic acid  turbidity (clot formation) due to hyaluronate
      • Metachromatic staining
        • Place fluid on filter paper + few drops of toluidine blue  metachromatic staining
iii physical examination
III. Physical Examination
  • Color:
    • Normal – clear, pale yellow
    • Red to brown: indicates trauma of procedure or disorder
    • Turbidity: associated with presence of WBCs
    • Milky: may indicate presence of crystals
  • Viscosity:
    • Measured at bedside by ability to form a string from tip of syringe
      • Normal: 4-6 cm
    • Ropes test (mucin clot test)– measurement of hyaluronate polymerization
      • Fluid forms a clot surrounded by clear fluid when added to acetic acid
      • Clot quality is reported:
        • Good = solid clot
        • Fair = soft clot
        • Poor = friable clot
        • Very poor = no clot
      • Test is of questionable precision and seldom used
iv microscopic examination
IV. Microscopic Examination
  • Cell Count – WBCs
    • Method
      • Use Neubauer counting chamber
      • May pretreat viscous fluids with hyaluronidase & incubate at 37oC for 5 min.
      • Dilution with hypotonic saline is used to lyse any RBCs OR
      • Dilute with normal saline/methylene blue mixture to differentiate WBCs from RBCs
    • Normal = <200 / uL
  • Differential Count
    • Cytocentrifuge specimen and prepare typical blood smear
    • Normal: 60% monocytes, macrophages

neutrophils: <20%

lymphocytes: <15%

(* values vary between texts)

    • Increased neutrophils – possible septic condition
    • Increased lymphocytes – indicate nonspetic inflammation
slide7
Other cell abnormalities:
    • Increased eosinophils – rheumatic fever, parasitic infections, metastatic carcinoma, post radiation therapy or arthrography
    • LE cells – patients with lupus erythematosus
    • Reiter cells – macrophages with ingested neutrophils
    • RA cells (ragocytes) – precipitated rheumatoid factor appearing as cytoplasmic granules in neutrophils
    • Hemosiderin granules – due to hemorrhagic process or cases of pigmented villonodular synovitis
    • Cartilaginous cells – observed in cases of osteoarthritis
    • Rice bodies – found in septic and rheumatoid arthritis and Tuberculosis
    • Fat droplets – indicate traumatic injury
slide12
Crystals
    • Crystal formation may be due to:
      • Metabolic disorders
      • Decreased renal excretion
      • Cartilage and bone degeneration
      • Medicinal injection (ex: corticosteroids)
    • Fluid is examined using the wet preparation technique
      • ASAP examination as pH and temperature affect observation
      • Ideally examined prior to WBC disintegration
      • Examine under both direct and compensated polarizing light
      • *may also be observed in Wright stain preparations
    • Under polarizing light (Direct polarization)
      • Birefringent substances appear as bright objects on a black background
      • Intensity varies between substances
    • Under compensated polarizing light
      • A red compensator plate is placed between the crystal and slide
      • Crystals aligned parallel to the compensator appear yellow (negative birefringence)
      • Crystals aligned perpendicular to the compensator appear blue (positive birefringence)
slide13
Monosodium Urate Crystals (MSU)
    • Indicate gouty arthritis due to:
      • Increased serum uric acid
      • Decreased renal excretion of uric acid
      • Impaired metabolism of nucleic acid
    • Exhibit negative birefringence
    • Intracellular (acute stages) & extracellular location
    • Polarized light – strongly birefringent
    • Compensated polarized light – yellow when parallel

blue when perpendicular

    • Needle shaped
  • Calcium pyrophosphate (CCPD)
    • Indicates pseudogout due to:
      • Degenerative arthritis
      • Endocrine disorders with increased serum calcium
      • Calcification of cartilage
    • Exhibit positive birefringence
    • Seen intracellular- and extracellularly
    • Polarized light – weakly birefringent
    • Compensated polarized light – blue when parallel (yellow when perpendicular)
    • Blunt rods or rhombic shapes
slide16
Cholesterol
    • Nonspecific indications
      • Associated with chronic inflammation
    • Exhibit negative birefringence (compensated polarized light)
    • Usually seen extracellularly
    • Polarized light – strongly birefringence
    • Rhombic plates
  • Hydroxyapatite (HA) (Calcium phosphate)
    • Associated with calcific deposition conditions
    • May produce an acute inflammatory reaction
    • Intracellular
    • Not birefringent
    • Require an electron microscope to examine
    • Small, needle shaped
  • Corticosteroid
    • Associated with intra-articular injections; NO clinical significance
    • Primarily intracellular
    • Exhibit positive and negative birefringence
      • Can closely resemble MSU and CCPD
    • Flat, variable shaped plates
slide17
Calcium Oxalate
    • Following renal dialysis
  • Birefringent Artifacts:
    • Anticoagulant crystals (calcium oxalate, lithium heparin)
    • Starch granules
    • Prosthesis fragments
    • Collagen fibers
    • Fibrin
    • Dust particles
v chemistry tests
V. Chemistry Tests
  • Glucose
    • Done simultaneously with blood sample (prefer 8 hour fast)
    • Difference between blood and synovial glucose values is evaluated
      • Normal = < 10 mg/dL
      • Inflammatory conditions = > 25mg/dL
      • Sepsis = >40 mg/dL
      • Considered low if < ½ serum plasma glucose value
    • Should be run within 1 hour of collection
    • Draw in sodium fluoride – prevents glycolysis
  • Total protein
    • Not routinely performed
    • Normal = < 1/3 of serum value (~3g/dL)
      • Large molecule, not easily filtered by membrane
    • Increased protein
      • Changes in membrane permeability
      • Increased joint synthesis
      • Indicates an inflammatory process
slide20
Uric Acid
    • Alone, not diagnostic
      • May determine gout in conjunction with plasma uric acid, esp. when crystals are undetectable
    • Normal = serum level
  • Lactate
    • May differentiate between inflammatory and septic arthritis
    • Septic arthritis = >250 mg/dL
    • Gonococcal arthritis = normal to low levels
    • Production results from :
      • Increased demand for energy
      • Tissue hypoxia
      • Severe inflammatory conditions
vi microbiology tests
VI. Microbiology Tests
  • Gram stain
    • Performed on all specimens
    • Most infections are bacterial:
      • Staphylococcus
      • Streptococcus
        • S. pyogenes
        • S. pneumoniae
      • Hemophilus
      • Neisseria gonorrhea
    • Fungal, viral and tubercular agents may also be observed
  • Culture
    • Routine culture
    • Enrichment medium (chocolate agar
    • Specialty media depending on clinician orders and indications
vii serologic tests
VII. Serologic Tests
  • Autoantibody detection (same as found in serum)
    • Rheumatoid arthritis (RA)
    • Lupus erythematosus (LE)
  • Antibody detection in patient’s serum
    • Borrelia burgdorferi
      • Causative agent of Lyme disease
      • Cause of arthritis
viii joint disorder classification
VIII. Joint disorder classification

Group Classification Significance

  • Noninflammatory Degenerative joint disorders
  • Inflammatory Immunologic problems (RA, LE) Gout & pseudogout (crystal induced)
  • Septic Microbial infection
  • Hemorrhagic Traumatic injury

Coagulation deficiency

Note:

* categories overlap

* multiple conditions can occur simultaneously

* disease stage can vary laboratory results

*see text for details of associated abnormal laboratory findings