1. Synovial Fluid
Synovial fluid is a plasma dialysate modified by constituents secreted by the joint tissues,
it is a viscous liquid found in small quantities in the spaces between the joints.
The fluid is produced by the inner membrane of the synovial joint ( synovial membrane) and secreted into the joint cavity .

2. Synovial Fluid Properties of the synovial fluid;
Volume of synovial fluid differs according to the size of joint it surrounds, the synovial fluid of the knee joint is around 3.5ml.
Viscosity is high and does not clot.
Appearance ; it is clear.
Colour; it is colorless – straw yellow.
pH 7.3 – 7.43.

3. Chemical composition Normal joint fluid chemical values Item Range
Mean pH
Total protein (g/dL)
Albumin (%)
Globulin (%)
Hyaluronate (g/dL)
Glucose (mg/dL)
Uric acid (mg/dL)
56-63
37-44
70-110
2-8
7.38
1.8 60 40
0.3

4. Hyaluronic acid; Normal synovial fluid contains 3-4 mg/ml of (hyaluronic acid), a polymer of disaccharides composed of D-glucuronic acid and D-N-acetyl glucosamine joined by alternating beta-1,4 and beta-1,3 glycosidic bond. Hyaluronan is synthesized by the synovial membrane and secreted into the joint cavity thus providing the synovial fluid with its characteristic viscous and elastic properties and lubricating the surfaces between synovium and cartilage, this high content of hyaluronic acid is a distinctive feature of the synovial fluid.
lubricin ; It is secreted by synovial cells , which also has a lubricating role.

5. Synovial Fluid Function of the synovial fluid ;
Synovial fluid forms a thin layer (roughly 50 µm) at the surface of cartilage and performing the following functions;
1-reduction of friction - synovial fluid lubricates the articulating joints thus reducing friction during joint movement .
2-shock absorption - as a dilatant fluid, synovial fluid is characterized by the rare quality of becoming more viscous under applied pressure. The synovial fluid in diarthrotic joints becomes thick the moment shear is applied in order to protect the joint and subsequently thins to normal viscosity instantaneously to resume its lubricating function between shocks.
3-nutrient/waste transportation - the fluid supplies oxygen and nutrients and removes carbon dioxide and metabolic wastes from the chondrocytes within the surrounding cartilage.
4-It also contains phagocytic cells that remove microbes and the debris that results from normal wear and tear in the joint.

6. Analysis of synovial fluid
Synovial fluid analysis is a group of tests that examine joint (synovial) fluid. The tests help diagnose and treat joint-related problems.
Removal of joint fluid has a dual purpose - diagnostic and therapeutic. Finding the cause of joint swelling is the diagnostic goal. The removal of fluid is the therapeutic goal , which may help relieve pain and pressure on the joint.
When is synovial analysis requested?
The test may be used to diagnose:
Gout
Infection
Other inflammatory joint conditions
Joint injury
Osteoarthritis
Synovial fluid can be collected by syringe in a procedure termed arthrocentisis , also known as joint aspiration.

7. Analysis of synovial fluid
Collection of the synovial fluid;
Synovial fluid can be collected by syringe in a procedure termed arthrocentisis , also known as joint aspiration.
The area of the joint from which the sample is to be withdrawn is cleaned and sterilized using betadine or povidine
( Precautions are taken so that bacteria is not introduced into the join)
After the area is cleaned, a local anesthetic is administered
Then health care provider will insert a sterile needle through the skin and into the joint space.
Once in the joint, fluid is drawn through the needle into a sterile syringe.
The fluid sample is sent to the laboratory for analysis.

8. Analysis of synovial fluid
after the withdrawal of the sample the doctor can inject medicine(usually a corticosteroid) into the joint using the same injection site , if needed.
The sample will then undergo ;
1- Appearance analysis;
The sample is observed by human eye for color and clarity. Normal joint fluid is viscous and appears clear to light yellow. Cloudy joint fluid is abnormal and suggestive of inflammation or an infection. Bloody joint fluid is also abnormal and may be caused by trauma to the joint.
2-Microscopic Examination:
The sample is examined under a microscope for the presence of blood cells, crystals, and bacteria. Normal joint fluid has none or few blood cells. Large numbers of red blood cells indicate bleeding in the joint. Large numbers of white blood cells can occur with infection, inflammatory arthritis, Gout.
Crystals are an abnormal finding. Uric acid crystals indicate gout . Bacteria is also abnormal. A culture can identify the source of infection.

9. Analysis of synovial fluid
3-Chemical Analysis:
The sample can also be tested for glucose, protein, and lactic dehydrogenase (LDH). Abnormal joint fluid results which may indicate inflammation or infection are:
· Glucose - less than 40 mg/dl
· Protein - greater than or equal to 3 g/dl
· LDH - great than 333 IU/L