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down to the joint capsule.
- Select an appropriate needle (usually 20-gauge for knee, shoulder, elbow, or ankle; 25 or 27-gauge for
small hand joints). - Stabilize the joint to be aspirated. Advance the needle into the joint space while continually applying
suction. Generally, a sudden “give” will be felt when the needle passes through the synovium into the
joint space. - Withdraw as much fluid as possible. Then withdraw the needle and apply firm pressure over the site
for 1-2 minutes. - Cover the site with an adhesive dressing.
Specific Joint Techniques
- Shoulder: Have patient sit with arm in lap (this positions the shoulder in mild internal rotation and
adduction). Identify insertion site inferior and slightly lateral to tip of coracoid. Direct the needle (20- or
22-gauge 1/2-in needle) to joint space medial to the head of the humerus and just below the palpable tip
of the coracoid process. - Wrist: Position the wrist in the prone position with about 20º of flexion. Identify insertion site by marking
the distal ends of the ulna and radius. Enter a bulging, inflamed joint space at the wrist dorsally at prominent
areas of swelling; such areas are invariably found on the radial or ulnar sides of the wrist during examination.
If possible, avoid inserting needles in the palmar or dorsal aspects of the wrist to prevent damaging nerves or
blood vessels over the joint. Use a 20- or 22-gauge 1/2-in needle. - Elbow: Have patient sit with the arm supported horizontal to the ground and the elbow bent at 30º.
Identify insertion site on the lateral aspect of the elbow in the shallow depression immediately anterior and
inferior to the lateral epicondyle of the humerus. Advance the needle medially and slightly proximally into
the joint space. With significant effusion, the bulging synovium should be evident laterally. CAUTION: Be
sure that it is not an olecronan bursitis, which would not require a joint procedure. Use a 20- or 22-gauge
1/2-in needle. - Knee: Place patient supine with quadriceps muscle relaxed (patella should be freely movable). Identify
the insertion site immediately beneath the lateral or medial edge of the patella. Enter the joint space of the
knee either medially or laterally. Pressure on the opposite side of the joint will make the synovium bulge more
prominently and toward the needle. Direct the needle parallel to the plane of the underside of the patella.
From the lateral aspect, the entrance site is at the intersection of lines extended from the upper and lateral
margins of the patella. Fluid should be obtained before the needle tip reaches midline. Use a 20- or 22-gauge
1/2-in needle.
Synovial Fluid Analysis
Record the physical characteristics or the fluid:
- Total volume
- Color and clarity (cloudy if you cannot read print held up behind it)
- Viscosity (joint fluid usually will stretch 1-2 inches)
Laboratory Studies:
- Cell count and differential
- Special stains: All fluids should have Gram stain. Special stains for fungi and acid-fast bacilli should also
be performed with chronic joint problems. - Examine for crystals: Examine the specimen immediately under the microscope.
- Culture: Sterile container holding 1-2 ml (GC requires special media)
- Fluid glucose: Low fluid glucose suggests infection (< 20 mg/dl).
- Protein content: High fluid protein indicates inflammation (Usually 1/3 of serum).
- Fat stain: Sudan stain (a few drops of glacial acetic acid and Sudan III in ethanol) positive indicates
presence of free fat that suggests intra-articular fracture