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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
Fluid formation Ultrafiltrate of plasma across synovial membrane
Non selective Excludes proteins of high molecular weight
Synoviocytes Secrete mucopolysaccharite which contains:
Hyaluronic acid protein
Cartilage & fluid function: Reduce friction between bones Lubricates joints Fluid provides nutrients to cartilage Lessens shock of walking and jogging impact
Synovial Fluid – Normal ValuesVolume <3.5 mLColor pale yellowClarity clearViscosity forms string 4-6 cm longErythrocytes <2000 cells/uLLeukocytes <200 cells/uLNeutrophils <20% of diff.Lymphocytes <15 % of diff.Monocytes & macrophages 65% of diff.Crystals NONEGlucose <10 mg/dL (lower than blood glucose)Lactate <250 mg/dLTotal protein <3 g/dLUric acid = blood value
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
Place fluid on filter paper + few drops of toluidine blue metachromatic staining
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 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
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
Synovial lining cell
Neutrophils in synovial fluid
Lymphs in synovial fluid
LE cell in synovial fluid
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)
Monosodium Urate Crystals (MSU) Indicate gouty arthritis due to:
Increased serum uric acid Decreased renal excretion of uric acid Impaired metabolism of nucleic acid
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
Acute gout (uric acid crystals)
Uric acid crystals
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