BIOCHEMISTRY OF SYNOVIAL FLUID

1. By
Dr KHALED ALGARIRI
CAMS- QASSIM UNIVERSITY
March 2020

2. Synovial Fluid Synovial
syn(like) + ovia (egg)
“Joint Fluid
Synovial fluid is necessary for normal joint function.
Synovial fluid moves into the cartilage when a joint
is resting, and moves out into the joint space when
the joint is active, particularly when the joint is
engaged in a weight-bearing activity such as exercise
INTRODUCTION

3. Synovial Fluid
Viscous fluid found in the cavities of
movable joints.
Synovial fluid is necessary for
normal joint function. Synovial
fluid moves into the cartilage when
a joint is resting, and moves out
into the joint space when the joint
is active, particularly when the
joint is engaged in a weight-bearing
activity such as exercise

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:
 Type A cells are macrophage-like and have primarily a phagocytic
function which is important to remove microbes and the debris that
results from normal wear and tear in the joint.
 Type B cells are fibroblast-like and produce hyaluronate, which
accounts for the increased viscosity of synovial fluid.
• Other cells found in the synovium include antigen-presenting cells
called dendritic cells and mast cells.
• .

6. Composition of Synovial Fluid
Synovial fluid is made of hyaluronic acid and lubricin, proteinases,
and collagenases.
Normal synovial fluid contains 3-4 mg/ml hyaluronate (hyaluronic
acid), a polymer of disaccharides composed of D-glucuronic acid and
D-N-acetylglucosamine joined by alternating beta-1,4 and beta-1,3
glycosidic bonds.
Synovial fluid also contains lubricin secreted 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 cell growth.

7. Functions of Synovial
 A- Supplying oxygen and nutrients of
articular cartilage by acting as a transport
medium for nutritional substances, such
as glucose.
 Articular cartilage has no blood, nerve, or
lymphatic supply.
 Supplying oxygen and nutrients to and
removing carbon dioxide and metabolic wastes
from the chondrocytes within articular
cartilage.
Synovial fluid is believed to have two main
functions:

9. Functions of Synovial
B- 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 hyaluronate or mucin and a glycoprotein in it.

10. Physical Characteristics of 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.

11. Physical Characteristics of Synovial Fluid
 Viscosity: Synovial fluid is very viscous due to its high
concentration of polymerized hyaluronic acid.
 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.

12. 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).

14. Physical Characteristics of Synovial Fluid
 Clot formation:
 Because of lack of fibrinogen and other clotting factors
synovial fluid doesn’t clot
 Inflammation allow the plasma clotting factors to escape in to
joint fluid which then clot

15. Microscopic Examinations
 Cell count and differential staining
Cell count should be finished without any delay to avoid clumping of
leukocytes.
• Degeneration of Leukocytes happens if stored morethan 1 hour after
sample collection
• If the sample is very thick , to facilitate cell counting sample can be
incubated at 37°C with hyaluronidase enzyme.
• RBCs are usually very low in number. Traumatic tap may result in high
number

16. Microscopic Examinations
 Types of cells seen
1-Lymphocytes
2- Synovial tissue cells
3-Polymorpho nuclear cells
4-Macrophages
5-Fat bodies
6-Bacteria

17. BIOCHEMICAL EXAMINATIONS
 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.
• Protein: Synovial fluid contains all proteins found in plasma, except various high–
molecular weight proteins.

18.  Increased synovial fluid protein levels are seen in ankylosing spondylitis, arthritis,
arthropathies that accompany Crohn disease, gout, psoriasis, Reiter syndrome,
and ulcerative colitis.
Reiter syndrome
ulcerative colitis
psoriasis

20. 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

21. 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/dL
but can be as high as 1000 mg/dL in septic arthritis.

22. • 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/dL but can be as
high as 1000 mg/dL in septic
arthritis.

23. 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.

24. 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.

25. 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.

27. 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.