Joint Aspiration (Arthrocentesis) Technique

Recommended needle gauge and length are discussed elsewhere (see Equipment). A larger needle size may be selected if a large effusion is noted or if purulent fluid or hemarthrosis is known or suspected. After aspiration, the patient should not immediately stand up but should rest for a few minutes to prevent unsteadiness.

Sometimes, no fluid or only a small amount of fluid enters the syringe. This may be because the needle is not in the joint capsule, because the fluid is too thick for the needle’s gauge, or because the needle is clogged with debris. In this situation, consider withdrawing and repositioning the needle or using a larger needle. Maintain moderate suction.

If the first syringe fills and fluid is still in the joint, switch to a fresh syringe without removing the needle from the joint. The hub of the needle can be firmly gripped with a hemostat, and then the filled syringe can be twisted off and a new one screwed on without disturbing the needle's position.

A study by Christensen et al found that about one third of patients undergoing total hip arthroplasty have dry hip aspirations and that in such cases, cultures are less well able to predict intraoperative findings. ^[10]

Nwawka et al found that the addition of joint lavage to native fluid collection in fluoroscopically guided aspiration of prosthetic joints may improve the sensitivity and specificity of diagnosis. ^[11]

Knee

The knee should be fully extended or just slightly bent up to 15°. The needle is held perpendicular to the leg and inserted medially beneath the patella at approximately the 2-o’clock to 3-o'clock position. (See the image below.) A lateral approach is also used in some cases (9-o'clock to 10-o’clock position).

The prepatellar pouch can be emptied by gently applying pressure and squeezing the soft tissues, starting from the midthigh and moving the hand towards the patella in order to shift the fluid toward the aspirating needle. Some have suggested that constant compression via circumferential mechanical pressure may yield improved results. ^[12]

A flexed-knee technique may be considered as an alternative for certain patients, such as those who are in wheelchairs, have flexion contractures, cannot be supine, or are otherwise unable to extend the knee. ^[13]

For more information, see Knee Arthrocentesis.

Shoulder

With the patient in a seated position, the arm is held comfortably at the patient’s side and externally rotated. The coracoid is palpated, and the needle is inserted approximately 1.5 in. (~4 cm) laterally and 1.5 in. (~4 cm) inferiorly. Alternatively, the shoulder can be approached posteriorly by inserting the needle inferior to the acromion. (See the image below.)

For more information, see Shoulder Arthrocentesis.

Wrist

The wrist is held in a straight line with the forearm. A dimple is palpated dorsally over the radiocarpal joint, which provides the entry point for the needle. The needle is held perpendicular to the forearm and inserted dorsally. (See the image below.)

For more information, see Wrist Arthrocentesis.

Elbow

The elbow is held in 90° flexion. The olecranon process, the lateral epicondyle, and the radial head are palpated. The needle is then inserted laterally into the triangle formed by these three structures. (See the image below.)

For more information, see Elbow Arthrocentesis.

Ankle

The ankle is held at 90° or slightly plantarflexed. A divot is palpated medial to the tibialis anterior, which provides the insertion site for the needle. The needle is inserted through an anterior approach. Alternatively, the joint can be approached anteriorly via the space palpated between the lateral malleolus and extensor digiti minimi. (See the image below.)

For more information, see Ankle Arthrocentesis.

Metacarpophalangeal joint

The finger is held slightly flexed. The needle is inserted dorsally and either medial or lateral to the extensor tendons. (See the image below.)

For more information, see Metacarpophalangeal Arthrocentesis.

Metatarsophalangeal joint

The toe is held slightly flexed. The needle is inserted dorsally and either medial or lateral to the extensor tendons.

For more information, see Metatarsophalangeal Arthrocentesis.

After aspiration of synovial fluid from a joint, it is important to make note of the appearance of the fluid. Normal fluid is clear to light yellow and is viscous. Inflammatory fluid is darker yellow to cloudy in appearance and loses its viscosity. Purulent fluid is coffee-colored to whitish and opaque.

A small amount of joint fluid can be placed on a microscope slide, covered with a cover slip, and then viewed immediately with a polarized light microscope.

The remaining synovial fluid can be sent to a laboratory for further analysis. Typical orders should include cell count, Gram stain, culture, and crystal analysis. Most commercial laboratories perform these tests on a green top (heparinized) tube. If more fluid is present or if septic arthritis is the leading differential, a sterile culture bottle should be used. In particular cases it may be appropriate to order a mycobacterial culture or a fungal culture.