Arthrocentesis

Relevant Social Security Medical Listings

• Listing 1.02 Major Dysfunction of a Joint (Adults)
• Listing 101.02 Major Dysfunction of a Joint (Children)
• Listing 14.09 Inflammatory Arthritis (Adults)
• Listing 114.09 Inflammatory Arthritis (Children)

Other Names

Closed Joint Aspiration, Joint Tap

Type

Objective/Surgical Procedure (Joint)

Can SSA Purchase?

No, but test results should always be considered as part of the evidence of record when provided by a treating doctor.

Purpose

Arthrocentesis involves analysis of joint effusions in order to:

• Diagnose non-inflammatory arthritis (e.g., osteoarthritis).
• Diagnose joint infections (septic arthritis).
• Monitor response to antibiotics used to treat septic arthritis.
• Diagnose inflammatory arthritis (e.g., gout, rheumatoid arthritis).

Contraindications

• Inability to identify the anatomical landmarks necessary to correctly position the needle.
• Skin or soft tissue infection in the area where the needle would have to be inserted.
• Inability or unwillingness of the patient to keep the joint still during the procedure.
• Inability to identify a joint effusion on physical examination prior to arthrocentesis.
• Joint space too difficult to reach, such as in obese patients.

Technique

Arthrocentesis involves inserting a needle into a joint space and withdrawing into a syringe all of whatever abnormal fluid is present. Only a local anesthetic is needed to control pain. Following the procedure, pressure is applied to the puncture site and the small needle hole is sealed with a small piece of adhesive tape. The fluid is then sent for laboratory analysis.

Complications

• Infection of the joint.
• Bleeding into the joint.
• Nerve, tendon, or cartilage injury.

Arthrocentesis is a safe procedure with few serious complications, especially in the easily accessible large joints such as the knee.

Interpretation

Normal Findings

In a normal joint, such a small amount of fluid is present that none can be drawn out (aspirated). Normal synovial fluid is clear and highly viscous as a result of the presence of a chemical called hyaluronic acid. Viscosity refers to the internal friction of a fluid; the higher the viscosity, the more the fluid tends to hold together. In the string test of synovial fluid viscosity, a drop of fluid is placed between two surfaces such as two microscope slides. As the slides are separated, the fluid between them will normally form a string about 3 inches long before breaking.

The mucin clot test is another test of synovial fluid viscosity. In this test, a synovial fluid sample placed in 5% acetic acid forms a firm clot that holds together when twirled with a wooden dowel rod. Results are reported as “good,” “fair,” or “poor.”

There are normally less than 200 white blood cells (WBC)/mm, and less than 25% of these WBCs are neutrophils. There are no malignant cells, lupus erythematosus (LE) cells, or other abnormal cells.

Chemically, the glucose content of normal synovial fluid is the same as blood glucose (65 – 110 mg/dl). Protein content is less than 3 grams/dl. Uric acid, the cause of gouty arthritis, is less than 8 mg/dl. LDH enzyme is present, but the same or less than that in blood. Hyaluronate content is about 0.3 – 0.4 grams/dl. Acidity (pH) varies from about 7.2 to 7.4.

There should be no microorganisms found—no viruses, fungi, or bacteria either by microscopic examination or culture.

Rheumatoid factor (RF) is negative. Complement is a protein important in the immune system whose level normally depends on the total protein content of the synovial fluid. Some diseases not only affect blood complement levels but also levels of complement in synovial fluid. Complement levels are interpreted by comparing synovial fluid complement to blood serum complement levels.

Abnormal Findings

Non-Inflammatory Joint Disorders – In non-inflammatory conditions such as osteoarthritis and trauma, there is a firm mucin clot in fluid that is clear or yellow-tinged. WBC count and chemistries such as glucose and LDH are normal, and there is no evidence of infection. Complement is normal.

Inflammatory Joint Disorders – Effusions resulting from inflammatory joint diseases result in a cloudy fluid, friable mucin clot, glucose levels lower than blood glucose, and elevated WBC counts of 5000 – 75,000 mm³ with greater than 50% neutrophils. For most inflammatory effusions, the complement level is 50% or more of the serum complement level. However, in systemic lupus erythematosus (SLE) and rheumatoid arthritis (RA) complement values less than 30% of expected normal are present. There are many diseases that can induce inflammatory arthritis including: connective tissue diseases such as systemic lupus erythematosus (SLE) and polymyositis; crystal-induced arthropathies such as gout and pseudogout; rheumatic fever and rheumatoid arthritis; arthritis related to inflammatory bowel disease; Reiter’s syndrome; psoriatic arthritis; and cancers such as leukemia and lymphoma.

Bloody Joint Disorders – Some types of effusions are grossly hemorrhagic (bloody). Gross blood in a joint is called hemarthrosis. These instances are related either to trauma (e.g., joint fractures into the joint space), disorders associated with excessive bleeding (e.g., thrombocytopenia, hemophilia), or excessive anticoagulation with drugs such as heparin being used to treat other disorders.

Infectious Joint Disorders – Septic arthritis refers to infection of a joint and these types of effusions have characteristic general patterns. WBC count is very high, usually between 50,000 – 1,000,000 mm³. Over 90% of these WBCs are neutrophils, except that in tuberculous (TB) arthritis as much as 50% of WBCs are lymphocytes. A frequent cause of septic arthritis is gonorrhea; staphylococcal bacteria are also a fairly common infecting organism. However, a wide possible range of bacteria as well as fungi can infect joints. Glucose levels are characteristically very low (less than half that of blood glucose); such low glucose levels are strongly suggestive of septic arthritis. The effectiveness of bacterial stains and cultures in diagnosing the causes of a septic joint vary with the type of bacteria. For example, Gram stain of staphylococcal bacteria may result in a positive microscopic diagnosis of the offending microorganism in the majority of cases, but Gram stains as well as culture are only diagnostic in about 25% of cases of gonococcal arthritis. On the other hand, septic arthritis caused by bacteria other than the gonococcus can be diagnosed, in some manner, in over 90% of cases. In septic arthritis, the joint fluid is extremely cloudy (turbid) and sometimes is purulent (containing pus).

There may be overlap in the general types of effusion described above. For example, effusions associated with lupus and acute rheumatic fever are usually inflammatory in nature but can present with a non-inflammatory profile; very early septic arthritis may not have an extremely depressed glucose level or elevated WBC level usually characteristic of an advanced infection.