Synovial Fluid Analysis
In arthrocentesis, a needle is used to withdraw (aspirate) synovial fluid, which is the viscous liquid that helps to lubricate and nourish bones and cartilage within the joints. The fluid sample is then sent to a laboratory for analysis. The most common site for arthrocentesis is the knee, but it can be performed on any major joint, including the shoulder, elbow, hip, ankle, and wrist. Arthrocentesis may also be done therapeutically to relieve pain and swelling caused by accumulation of fluid in a joint.
Purpose of the Arthrocentesis
- To aid in the diagnosis of certain joint disorders such as infection, rheumatoid arthritis, and gout
- To determine the cause of joint inflammation or effusion (excessive accumulation of fluid inside the joint)
- To monitor the effectiveness of antibiotic medication used for the treatment of infectious arthritis
- Performed therapeutically to relieve the discomfort caused by joint effusion or to administer medications, such as corticosteroids, into the joint
- To look for crystals in joint fluid (sign of gout)
Who Performs Arthrocentesis
- A physician
Special Concerns about Arthrocentesis
- Arthrocentesis should not be performed in areas with a skin or wound infection.
- This procedure may be done in a hospital or in an outpatient setting.
- Sometimes a blood sample is taken from a vein in the arm (called venipuncture) to compare chemical test results with analyses of the synovial fluid obtained during arthrocentesis.
- Your doctor may ask you to avoid food and fluids for 6 to 12 hours if glucose levels in the synovial fluid are to be measured. If not, fasting is unnecessary.
- You will be instructed to remove whatever clothing is covering the joint to be aspirated.
What You Experience
- The skin at the site of needle insertion is cleansed with an antiseptic solution, and a local anesthetic is injected to numb the area.
- The area around the joint may be wrapped in elastic bandages to compress the maximum amount of fluid into the joint space.
- A needle is quickly inserted through the skin and into the joint space. You will feel pressure or slight pain as it is inserted.
- Fluid is withdrawn through the needle and placed into multiple specimen containers.
- If a corticosteroid or another medication (such as an antibiotic) is administered, the syringe is detached, leaving the needle in the joint. Another syringe is then attached, and the medicine is injected.
- The procedure takes 3 to 5 minutes.
Risks and Complications of Arthrocentesis
- Serious but rare complications include infection or bleeding in the joint area.
- Infection or injury to nearby skin
- The needle is withdrawn and pressure is applied to the puncture site with sterile gauze pads for 3 to 5 minutes.
- A pressure bandage is then applied to avoid re-collection of fluid or accumulation of blood underneath the skin (hematoma).
- Apply ice or cold packs to the joint for 24 to 48 hours to reduce any swelling and pain. You may also be given pain-relieving medication.
- You may resume your normal activities, but try to avoid excessive use of the affected joint for several days.
- Contact your doctor immediately if you develop increased pain or fever, skin redness, swelling, excessive bleeding or discharge at the site of the arthrocentesis.
- The specimen containers may be sent to several different laboratories for examination, and the fluid is analyzed for the presence of abnormal components. For example, bacteria may be present in cases of infectious arthritis, elevated white blood cells suggest an inflammatory disorder such as rheumatoid arthritis, and uric acid crystals indicate a diagnosis of gout.
- If a definitive diagnosis can be made, the doctor will recommend an appropriate course of treatment.
- In some cases, additional tests may be required to establish a diagnosis or determine the extent of a problem.
The Johns Hopkins Consumer Guide to Medical Tests
Simeon Margolis, M.D., Ph.D., Medical Editor
Updated by Remedy Health Media