Synovial fluid is a viscous, non-Newtonian fluid found in the cavities
of synovial joints.
With its yolk-like consistency, the principal role of synovial fluid is to
reduce friction between the articular cartilage of synovial joints during
The inner membrane of synovial joints is called the synovial
membrane and secretes synovial fluid into the joint cavity
The fluid contains hyaluronic acid secreted by fibroblast-like cells in
the synovial membrane and interstitial fluid filtered from the blood
This fluid forms a thin layer (roughly 50 μm) at the surface of cartilage
and also seeps into micro-cavities and irregularities in the articular
cartilage surface, filling all empty space.
During movement, the synovial fluid held in the cartilage is squeezed
out mechanically to maintain a layer of fluid on the cartilage surface
(so-called weeping lubrication).
Functions of Synovial Fluid
Reduction of friction - synovial fluid lubricates the
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.
Nutrient and waste transportation - the fluid
supplies oxygen and nutrients and removes
carbon dioxide and metabolic wastes from
the chondrocytes within the surrounding cartilage.
Reasons for Synovial Fluid
Joint aspiration may be performed to diagnose and assist in the
treatment of joint disorders and/or problems. By analyzing the fluid
obtained during the procedure, the following conditions may be
Various types of arthritis
Joint aspiration can also be performed to remove a large
collection of fluid around a joint. Sometimes bursitis (inflammation of
the bursa) causes fluid to collect in a joint. Removing the fluid will
decrease the pressure, relieve pain, and improve movement of the
joint. Sometimes, a medication is injected into the joint following
removal of the fluid to help treat tendonitis or bursitis.
Risks involved in Synovial fluid
complications can occur. Some possible
complications may include, but are not
limited to, the following:
Discomfort at the aspiration site
Bruising at the aspiration site
Swelling at the aspiration site
Infection at the aspiration site
Precautions before aspiring
Doctor should explain the procedure to the patients and offer the
opportunity to ask any questions that they might have about the
procedure. Laboratory staff should also guide the patient about the
test and procedure of drawing the sample.
Patients are asked to sign a consent form that gives permission to do
The laboratory staff should notify if patient is sensitive to or are
allergic to any medications, latex, tape, and anesthetic agents (local
The laboratory staff should also notify all medications (prescribed and
over-the-counter) and herbal supplements that the patients are
The laboratory staff should also note if the patient have a history of
bleeding disorders or if patient is taking any anticoagulant (bloodthinning) medications, aspirin, or other medications that affect blood
clotting. It is necessary to stop these medications prior to the
Generally, no prior preparation, such as fasting or sedation is
During Synovial Fluid Aspiration
A joint aspiration may be performed on an outpatient basis. Procedures
may vary depending on patient’s condition. Generally, a joint
aspiration procedure follows this process
Patient should be positioned so that the doctor/technician can easily
reach the joint that is to be aspirated.
The skin over the joint aspiration site should be cleansed with an
If a local anesthetic is used, patient will feel a needle stick when the
anesthetic is injected. This may cause a brief stinging sensation.
The doctor/technician will insert the needle through the skin into the joint.
Patient may feel some discomfort or pressure.
The doctor/technician will remove the fluid by drawing it into a syringe
that is attached to the needle.
The needle will be removed and a sterile bandage or dressing will be
The fluid sample is sent to the lab for examination.
After Synovial Fluid Aspiration
Once sample is drawn, it is important for the patient to
keep the joint aspiration site clean and dry.
The aspiration site may be tender or sore for a few days
after the joint aspiration procedure.
Take a pain reliever for soreness as recommended by
the doctor. Aspirin or certain other pain medications may
increase the chance of bleeding. Be sure to take only
The patient should be guided to report to the doctor in
any of the following conditions after fluid aspiration
Redness, swelling, bleeding, or other drainage from the
Increased pain around the aspiration site
Specimen handling and
Synovial fluid is present in all joints but usually it is
collected from the knee joint. Normal amount of
fluid contained in the knee cavity is less than
3.5mL; however this amount increases in joint
disorders. The sample collected is dependent
upon amount of fluid build up in the joints.
Normally samples are collected in three tubes.
EDTA tubes – for Cell count and differentials
Heparinized tubes – Chemical and Immunologic tests
Sterile tubes – Crystal examination and Microbiological
Laboratory Tests of Synovial Fluid
Following are the tests performed of Synovial joints fluid.
Gross examination for color and clarity
Clear and light yellow – Normal
Turbid or cloudy – elevated cell count, crystals, cartilage debris
Hemorrhagic fluid – homogenously bloody
Traumatic aspirate – streaks of blood
Color – varies based on bacterial infection, cell or crystal presence
Leukocyte count and differential (Place sample under a microscope,
count the number of red and white blood cells, and then looks for
crystals (in the case of gout or bacteria)
Measure glucose, proteins, uric acid, and lactic dehydrogenase
Culture the fluid to see if any bacteria grows
Classification of Synovial Fluid
Similar to blood
Similar to blood