Synovial Fluid Composition a short lecture

Composition of the Synovial Fluid

1. SYNOVIAL FLUID COMPOSITION

2. INTRODUCTION
•Synovial fluid is a thick, stringy fluid found in the cavities of synovial
joints.
•With its egg-like consistency ("synovial" partially derives from ovum,
Latin for egg), synovial fluid reduces friction between the articular
cartilage and other tissues in joints, to lubricate and cushion them
during movement.
•The inner membrane of synovial joints is called the synovial
membrane and secretes synovial fluid into the joint cavity.
•This fluid forms a thin layer (roughly 50 μm) at the surface of
cartilage.

3. SYNOVIAL JOINT
•Plasma constituents that enter
joint fluid must cross a double-
barrier membrane.
•First, the endothelial lining of the
capillaries is traversed followed by
movement through a matrix that
surrounds synovial cells.
•This ultrafiltrateis combined with
a mucopolysaccharide
(hyaluronate) synthesized by the
synovium.

4. Synovial fluid electrolytes
•The distribution ratio of most electrolytes between
synovial fluid and serum is 1.
•The average ratio of total anions of serum to total
anions of synovial fluid is 1.99.
•Ionic calcium ratios are approximately 1.18.
•This higher ratio is thought to be due to the base
combining power of mucinfor calcium.

5. Secretion of Synovial Fluid
Synovial tissue is composed of connective tissue that lacks a
basement membrane.
There are two main types of synovial lining cells:
oType A cells are macrophage-like and have primarily a
phagocyticfunction which is important toremove microbes and
the debris that results from normal wear and tear in the joint.
oType B cells are fibroblast-like and produce hyaluronate, which
accounts for the increased viscosity of synovial fluid.
•Other cells found in thesynoviuminclude antigen-presenting
cells called dendritic cells and mast cells.
•Synovial tissue also contains fat and lymphatic vessels,
fenestrated microvessels, and nerve fibers derived from the
capsule and periarticular tissues.

6. Secretion of Synovial Fluid
•Synovial fluid is made ofhyaluronicacid and lubricin,
proteinases, and collagenases.
•Normal synovial fluid contains 3-4 mg/ml hyaluronate
(hyaluronicacid), a polymer of disaccharides composed
of D-glucuronicacid and D-N-acetylglucosaminejoined
by alternating beta-1,4 and beta-1,3 glycosidicbonds.
•Synovial fluid alsocontains lubricinsecreted by
synovial cells. It is chiefly responsible for so-called
boundary-layer lubrication, which reduces friction
between opposing surfaces of cartilage. It may also
have a role in synovial cellgrowth.

7. FUNCTIONS
Synovial fluid is believed to have two main functions:
To aid in the nutrition of articular cartilage by acting as a
transport medium for nutritional substances, such as
glucose.
•Articular cartilage has no blood, nerve, or lymphatic supply.
Supplyingoxygen and nutrients to and removingcarbon
dioxide and metabolic wastes from the chondrocyteswithin
articularcartilage.
•Glucose for articular cartilage chondrocyte energy is
transported from the periarticularvasculature to the
cartilage by the synovial fluid.

8. FUNCTIONS
To aid in the mechanical function of joints by
lubrication of the articulating surfaces.
•Lubrication reduces frictional resistance between
bearing surfaces by keeping them apart.
•During movement, the synovial fluid held in the
cartilage is squeezed out mechanically to maintain a
layer of fluid on the cartilage surface.
•The lubricating properties of synovial fluid on articular
cartilage are due to the presence of hyaluronateor
mucinand a glycoprotein in it.

9. Physical Characteristics of Normal
Synovial Fluid
•Normal synovial fluid is clear, pale yellow, viscid,
and does not clot.
•Volume: The amount of fluid contained in joints is
usually small. The knee joint normally contains up
to 4 mL of fluid.
An increase in synovial fluid enough to aspirates is
due to some disease.

10. Clotting
•Normal synovial fluid: Do not clot
•Clotting of synovial fluid means fibrinogen is
present:
1.Damaged synovial membrane
2.Traumatic tap

11. Color and clarity:
•Normal synovial fluid is colorless and clear.
•Other appearances may indicate various disease
states.
•Loss of clarity : crystals, increased cellularity,
infective, cartilage debris
•E.g. Yellow/clear (non inflammatory effusions),
yellow/cloudy (inflammatory processes), white/
cloudy (crystals); and red brown (hemorrhage).

12. Physical Characteristics of Normal
Synovial Fluid
•Viscosity: Synovial fluid is very viscous due to its high
concentration of polymerized hyaluronate.
•A string test can be used to evaluate the level of synovial fluid
viscosity. After removing the needle or cap from the syringe,
synovial fluid is expressed into a test tube one drop at a time.
•Normal synovial fluid will form a “string” approximately 5 cm
long before breaking.
•In addition, the fluid may cling to the side of the test tube rather
than running down to the bottom.
•Low viscosity of synovial indicates the presence of an
inflammatory process.

13. Physical Characteristics of Normal
Synovial Fluid
•Temperature –32 degree Celsius (peripheral
joints are cooler than core body temperature).
•pH –7.4

14. Indications
•Suspected septic arthritis
–Any febrile person with unexplained inflammatory fluid ->
presumed septic joint
–Even with acute flare of arthritis (e.g., RA), should rule out septic
joint
•Suspected crystal-induced arthritis
–Gout or pseudogoutdiagnosis largely made with microscopic
examination
–Diagnosis requires negative Gram stain/culture
•Unexplained joint or bursa swelling
–Largely to permit classification into inflammatory vs
noninflammatorycategories
–Diagnosis made along with history & physical.

15. BIOCHEMICAL EXAMINATION
•Protein: Synovial fluid contains all proteins found in plasma,
except various high–molecular weight proteins.
•These high–molecular-weight proteins include fibrinogen,
beta 2 macroglobulin, and alpha 2 macroglobulin, and can
be absent or present in very low amounts.
•Most commonly used serum protein procedures can be
used to measure synovial fluid protein.
•The normal range for synovial fluid protein is 1–3 g/dL.
•Increased synovial fluid protein levels are seen in ankylosing
spondylitis, arthritis, arthropathies that accompany Crohn
disease, gout, psoriasis, Reiter syndrome, and ulcerative
colitis.

16. BIOCHEMICAL EXAMINATION
•Glucose: Synovial fluid glucose levels should be interpreted
using serum glucose levels.
•A fasting specimen should be used or at least one 6–8 hours
postprandially.
•Normally, synovial fluid glucose levels are less than 10
mg/dL lower than serum levels.
•Joint disorders that are classified as infectious demonstrate
large decreases in synovial fluid glucose and can be as much
as 20–100 mg/dL less than serum levels.
•Other groups of joint disorders demonstrate a less of a
decrease in synovial fluid glucose, 0–20 mg/dL

17. BIOCHEMICAL EXAMINATION
•Uric acid: Synovial fluid uric acid normally ranges from 6 to 8
mg/dL.
•The presence of uric acid in synovial fluid is helpful in diagnosis
gout.
•Usually, crystal identification is used for this determination, but
synovial fluid uric acid levels may be performed in laboratories
that do not have a light polarizing microscope.
•Lactic acid: Lactic acid is rarely measured in synovial fluid but can
be helpful in diagnosing septic arthritis.
Lactate levels in the synovial fluid have the highest
diagnostic potential for predicting septic arthritis.
•Normally, synovial fluid lactate is less than 25 mg/dLbut can be
as high as 1000 mg/dLin septic arthritis.

18. BIOCHEMICAL EXAMINATION
•Enzymes: Alkaline phosphatase, acid phosphatase,
lactic dehydrogenase, and other enzymes are present
in detectable quantities.
•Synovial fluid to serum ratios of these and other
enzymes vary with the presence of articular disease.
•Enzymes enter the synovial fluid directly from the
plasma or may be produced locally by the synovial
membrane or released by synovial fluid macrophages.

19. BIOCHEMICAL EXAMINATION
•Lactate dehydrogenase: Lactate dehydrogenase (LD)
can be elevated in synovial fluid, while serum levels
remain normal.
•Synovial fluid LD levels are usually increased in RA,
infectious arthritis, and gout.
•The neutrophils that are increased during the acute
phase of these disorders contribute to this increased
LD level.

20. BIOCHEMICAL EXAMINATION
•Complement levels: Normal synovial fluid complement
levels in humans are approximately 10% of the serum
values.
•In the inflamed joint synovial fluid complement levels
will vary. The long-term patterns of variation have
some prognostic value in human rheumatoid arthritis
patients.
•Rheumatoid factor (RF) is an antibody to
immunoglobulins.
•RF is present in the serum of most patients with RA,
whereas just more than half of these patients will
demonstrate RF in synovial fluid.

22. CLINICAL IMPORTANCE
•Synovial fluid analysis is a well-established
procedure in the evaluation of joint disease.
•The purpose of synovial fluid analysis is to
determine the presence of arthritis and to place a
fluid into one of several categories.
•Appropriate treatment of joint disease depends on
proper identification of disease.

23. Practice Questions

24. Q1) Which of the following cells in the synovium
increases the viscosity of synovial fluid?
a)Type A cells (macrophage-like)
b)Type B cells (fibroblast-like)
c)mast cells
d)dendritic cells

25. key: b
a)TypeAisderivedfrombloodmonocytes,anditremovesthewear-and-
teardebrisfromthesynovialfluid.
b)TypeBproduceshyaluronan.Synovialfluidismadeofhyaluronicacid
andlubricin,proteinases,andcollagenases.Synovialfluid
containslubricin(alsoknownasPRG4)asasecondlubricating
component,secretedbysynovialfibroblasts
c)&d).
–NormallySynovialFluidhas..NOleukocytes(whitebloodcells)
NOredbloodcellsNOplasmaclottingfactorsNOculture(no
bacteria)NOchondrocytes
–Inpathologicfluids,chondrocytes,osteoblasts,andosteoclastsmay
beseen.

26. Q2) Which test can be used to evaluate the level
of synovial fluid viscosity?
a)String test
b)Gram staining
c)Coagulation test
d)Illumination test

27. key: a
a)String sign is used for the measure of viscosity
–1-2 inches ; When a drop is taken between the thumb and finger as
in pinching and then they are separated, the drop forms a string
till 1-2 inches
b)Gram stainis used to distinguish and classifybacterialspecies into
two large groups
c)Cogulation test is used to assess bloodclottingfunction.
d)TheIllumination& VisibilityTestingLaboratory is used for
conducting photometric measurements and human visual
performance

28. Q3) The presence of uric acid in synovial fluid is
helpful in diagnosis of:
a)Gout
b)Rheumatoid arthritis
c)Septic arthritis
d)Osteoarthritis

29. key: a
a)Goutarthritisiscausedbythedepositionofcrystals
ofuricacidinajoint.
b)Rheumatoidarthritis(RA)isanautoimmunedisease
c)Septicarthritisisapenetratinginjurydeliversgerms
directlyintothejoint.
d)Osteoarthritisisadegenerativedisorderofjoints.

30. Q4) In which joint condition does the synovial
fluid examination shows WBC count more
than 50,000 per ml?
a)Osteoarthritis
b)gout
c)trauma
d)gonococcal septic arthritis

31. key: d
a)Osteoarthritisisthedegenerativedisease
b)Goutarthritisiscausedbythedepositionofcrystalsofuricacid
inajoint.
c)TraumadoesnotelevatetheWBCcount
d)Synovialfluidwhitebloodcellcountinpatientswithseptic
arthritisisusuallygreaterthan50,000permm.

32. Q5). The highest diagnostic potential for
predicting septic arthritis in synovial fluid is:
a)Acetate
b)Lactate
c)Pyruvate
d)Uric acid

33. key: b
a)Normally, synovial fluid glucose levels are less than 10 mg/dL
lower than serum levels. So, Acetate will be not increased.
b)The highest concentrations oflactateoccurred in non-
gonococcalsepticsynovial fluids. Lactate levels in the synovial
fluid have the highest diagnostic potential for predicting septic
arthritis.
c)Normally, synovial fluid glucose levels are less than 10 mg/dL
lower than serum levels. So, pyruvate will be not increased.
d)The presence of uric acid in synovial fluid is helpful in
diagnosis gout.