Post on 22-Dec-2015
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
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
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 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
smear Normal: 60% monocytes, macrophages
neutrophils: <20%lymphocytes: <15%
(* values vary between texts)
Increased neutrophils – possible septic condition Increased lymphocytes – indicate nonspetic
inflammation
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
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
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
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
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 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
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 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
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
Group Classification SignificanceI. Noninflammatory Degenerative joint disordersII. Inflammatory Immunologic
problems (RA, LE) Gout & pseudogout (crystal
induced)III. Septic Microbial infectionIV. Hemorrhagic Traumatic injury
Coagulation deficiencyNote:
* categories overlap* multiple conditions can occur simultaneously* disease stage can vary laboratory results
*see text for details of associated abnormal laboratory findings