Synovial Fluids

What is synovial fluid, and what are its three main functions?

A viscous fluid in the cavities of movable joints; it helps reduce friction as joints move, provides nutrients to cartilage, and reduces shock during movement.

What surrounds the joint, and what types of cells is it composed of?

The synovial membrane, composed of synoviocytes — Type A (macrophage-like) and Type B (fibroblast-like).

What do synoviocytes secrete?

Hyaluronic acid and protein (fibronectin and collagen).

Slide 3: Composition

What is synovial fluid derived from, and what does it exclude?

An ultrafiltrate of plasma; it excludes high molecular weight proteins.

What is the chemical composition of synovial fluid, and what additional substance does it contain?

Chemical composition is close to plasma, but it also contains hyaluronic acid.

What conditions can influence the permeability of synovial fluid?

Immunological conditions, mechanical conditions, and bacterial infections.

Slide 4: Conditions Involving Synovial Fluid

What are the four classification groups of joint disorders?

Inflammatory (e.g., RA, SLE, ankylosing spondylitis), non-inflammatory (e.g., osteoarthritis — cartilage breakdown), infectious, and hemorrhagic (e.g., trauma, hemophilia, tumors).

Slide 5: Gout

What crystals are associated with gout, and what causes it?

Monosodium urate (uric acid) crystals; caused by increased intake of purines, impaired metabolism of purines, chemotherapy, or renal issues that impair uric acid excretion.

What is the demographic most commonly affected by gout?

The most common inflammatory disease of men over 40; male:female ratio of 7:1.

Slide 5: Pseudogout

What crystals are associated with pseudogout, and what conditions are linked to it?

Calcium pyrophosphate dihydrate (CPPD) crystals; may be seen in degenerative arthritis or disorders with increased calcium levels.

How common is pseudogout compared to gout?

Less common than gout.

Slide 6: Specimen Collection

Who collects synovial fluid, and how much is typically obtained?

Collected by a physician; several drops to several mL.

What tube is used for chemistry testing of synovial fluid?

A plain tube (no anticoagulant).

What tube is used for cell counts and crystal examination of synovial fluid?

EDTA or heparin tube.

What tube is used for microbiology of synovial fluid?

SPS or heparinized tube.

Slide 7: Synovial Fluid Appearance

What does normal synovial fluid look like?

Clear and pale yellow.

What does a deeper yellow or greenish color in synovial fluid indicate?

Deeper yellow indicates inflammation; greenish color suggests bacterial infection.

What causes turbidity in synovial fluid?

WBCs and synovial cell debris.

What does a milky appearance in synovial fluid indicate?

Presence of crystals.

What must be differentiated when synovial fluid appears bloody?

A true bleed vs. a traumatic aspiration; blood streaks may indicate a traumatic tap.

Slide 8: Synovial Fluid Viscosity

Why is normal synovial fluid viscous, and how is viscosity assessed?

Due to hyaluronic acid polymerization; the fluid should drip to form a 4–6 cm string before breaking (this may be done at bedside).

What does decreased viscosity in synovial fluid indicate, and why does it occur?

Indicates arthritis, which affects hyaluronic acid production and its ability to polymerize.

Slide 9: Synovial Fluid Cell Count

What is the normal WBC count in synovial fluid, and how is it performed?

Normal WBC count is <200/µL; performed using a hemocytometer.

What type of dilution must be used for synovial fluid cell counts, and why?

Saline must be used for dilutions (dilutions are needed when the sample is turbid or bloody).

What can be used to help with viscous samples before the cell count, and when is it used?

Hyaluronidase — sometimes used when samples are extremely viscous to help liquefy them for the cell count.

Slide 10: Synovial Fluid Differential

What cells make up the normal synovial fluid differential?

Mostly monocytes or macrophages, some neutrophils, and occasional lymphocytes.

What other cells may be seen in synovial fluid?

Synoviocytes, macrophages with hemosiderin, malignant cells, and cartilage cells.

Slide 11: Crystals in Synovial Fluid — Overview

What effect do crystals in synovial fluid typically cause?

Usually cause acute, painful inflammation.

What are the causes of crystal formation in synovial fluid?

Metabolic disorders and decreased renal excretion.

Why is crystal identification clinically important in synovial fluid?

It assists with differential diagnosis — for example, distinguishing gout from pseudogout.

Slide 12: Common Crystals — Monosodium Urate (MSU)

What condition is monosodium urate (MSU) associated with, and what causes it?

Associated with gout; caused by purine metabolism disorders, increased purine consumption, or chemotherapy.

What is the shape and location of MSU crystals?

Needle-shaped; can be intracellular or extracellular.

Slide 12: Common Crystals — Calcium Pyrophosphate Dihydrate (CPPD)

What condition is CPPD associated with, and what causes it?

Associated with pseudogout; caused by degenerative arthritis or endocrine disorders with increased serum calcium.

What is the shape and location of CPPD crystals?

Rhombic; intracellular.

Slide 13: Other Crystals and Artifacts

What other crystals may be found in synovial fluid besides MSU and CPPD?

Cholesterol, corticosteroids, and calcium oxalate.

What artifacts may be seen in synovial fluid crystal examination?

Talc, starch, precipitated anticoagulants, dust, and scratches on slides.

Slide 14: Crystal Identification — Procedure

Why should crystal examination be performed as soon as possible?

To avoid changes from temperature and pH, which can alter crystals.

How should crystals be observed microscopically?

Observe unstained under polarized light; scan on low power first.

If crystals are present on low power, what is the next step?

Examine using red compensated polarization.

What must be reported for MSU and CPPD crystals specifically?

Whether they are extra- or intracellular.

Slide 15: Crystal Appearance Under Polarization

Under red compensated polarization, how do MSU (gout) crystals appear based on orientation?

Yellow when parallel to the quartz compensator line; blue when perpendicular to the quartz compensator line.

Under red compensated polarization, how do CPPD (pseudogout) crystals appear based on orientation?

Yellow when perpendicular to the quartz compensator line; blue when parallel to the quartz compensator line (opposite of MSU).

Slide 16: Additional Testing

What chemistry tests may be ordered on synovial fluid?

Glucose, lactic acid (helpful for identifying bacterial infection), uric acid, and enzymes (may be used to monitor rheumatoid arthritis).

What other testing may be ordered on synovial fluid to help identify infectious organisms?

Microbiology, serology, and molecular te