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

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

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

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

Calcium Oxalate Following renal dialysis

Birefringent Artifacts: Anticoagulant crystals (calcium oxalate, lithium

heparin) Starch granules Prosthesis fragments Collagen fibers Fibrin Dust particles

                                                                                                                

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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