Joint Aspiration (Arthrocentesis)

Aspiration of a joint (arthrocentesis) with subsequent analysis of the synovial fluid is a critical component in diagnosing arthritis.[1, 2] Analysis of the joint fluid can differentiate an inflammatory arthritis from a noninflammatory arthritis. A definitive diagnosis of crystalline arthritis or septic arthritis can be made only by means of joint aspiration.

Joint aspiration is a relatively quick and inexpensive procedure to perform. It can be done in an office setting or in a hospital. No particular certification is required to perform arthrocentesis; it can be done by any physician, physician’s assistant, or advance practice nurse who has the appropriate training and equipment. Initial analysis of the fluid can be performed in the office with the use of a polarized light microscope.

Joint aspiration should be considered for any patient with an inflamed joint or joints who does not have an established diagnosis. Inflamed joints are recognized by being red, warm, tender, swollen, and painful to bend.

A joint presenting as acute monoarthritis should always be aspirated if infection is suspected upon clinical evaluation. Patients with preexisting arthritis (eg, rheumatoid arthritis or gout) are at increased risk for the development of septic arthritis. Therefore, aspiration must be performed whenever there is suspicion of an infected joint in patients with known arthritis.

Repeated aspirations can be part of the management of a septic joint to relieve discomfort and prevent joint damage. Aspiration can be considered in cases of hemarthrosis to prevent adhesions. Aspiration can be performed immediately prior to injecting intra-articular medications such as corticosteroids to improve efficacy.

As a rule, if joint aspiration is being considered, it should probably be performed.

According to Infectious Diseases Society of America (IDSA) guidelines on management of prosthetic joint infection (PJI), diagnostic arthrocentesis should be performed for any suspected acute PJI unless the diagnosis is clinically evident, surgery is planned, and antibiotics can safely be withheld preoperatively.[3] It is also advised in patients with a chronic painful prosthesis who have unexplained elevations of erythrocyte sedimentation rate or C-reactive protein level or in whom PJI is clinically suspected (though it may not be necessary in all cases).

In this setting, synovial fluid analysis should include a total cell count and differential leukocyte count, as well as culture for aerobic and anaerobic organisms.[3] A crystal analysis can also be performed if clinically indicated.

Repeat aspiration may be warranted in joint-replacement patients with conflicting clinical data and a prior history of PJI, with suspected adverse local tissue reaction, or with high clinical suspicion of infection.[4, 5]

No strict contraindications for arthrocentesis are recognized; however, caution is advised in certain situations.

A needle should not be passed through an area of infection (eg, overlying cellulitis) before entering a joint, because seeding infection into the joint capsule may occur.

Patients who are anticoagulated or have a bleeding diathesis (eg, hemophilia or thrombocytopenia) are at increased risk for hemarthrosis. It has been recommended that when possible, aspiration should be delayed until the coagulopathy is reversed, and that when a delay is not possible, the physician should be prepared to treat bleeding (eg, with appropriate factor concentrates in a hemophiliac patient).

However, some studies have found arthrocentesis to be safe in patients receiving anticoagulant therapy.[6, 7, 8]

When aspiration of artificial joints is necessary, it is generally handled by an orthopedic surgeon.

When a clinical need to aspirate a joint is present in a patient with overlying infection or coagulopathy, the physician must weigh the risks and benefits of aspiration in their decision whether to proceed with arthrocentesis.

Any joint can be aspirated; however, some joint aspirations require the use of ultrasonographic or fluoroscopic guidance.[9] Ultrasonography allows the clinician to confirm the presence of fluid before aspirating. It can also be helpful in aspirating deep or technically difficult joints. The hip joint should be aspirated under ultrasonographic guidance. Joints of the spine, including the sacroiliac joint, should be aspirated under fluoroscopic guidance. Guidance for aspiration is also recommended when blind attempts have failed to access any joint fluid.

Verbal consent is usually sufficient for joint aspiration (arthrocentesis). The patient should be informed of the risks of the procedure, which include the rare occurrence of bleeding into the joint, fainting, or infection. The risks of not performing arthrocentesis include failure to make the diagnosis and the consequent associated morbidity. Any allergy (eg, to preparation material used or latex gloves) must be investigated.

Personal protective equipment includes the following:

• Gloves
• Face shield (optional)

Anesthesia equipment includes the following:

• 1% lidocaine solution
• 25- or 27-gauge needle

Sterilization materials include the following:

• Povidone-iodine solution or chlorhexidine
• Alcohol wipes

Aspiration materials include the following:

• 1.5-in. (3.8-cm) 21- to 18-gauge needle for large joints (eg, knee, ankle or shoulder)
• 1-in. (2.5-cm) 21-gauge needle for medium joints (eg, wrist)
• 1-in. (2.5-cm) 25-gauge needle for small joints (eg, metacarpophalangeal [MCP] or metatarsophalangeal [MTP])
• Longer needles if needed for deep joints or very obese patients
• 3-, 10-, or 20-mL syringe, as appropriate for the joint and the size of the effusion
• Adhesive bandage
• Sterile gauze
• Heparinized (green top) tubes and sterile culture bottles (optional)　

Before the procedure is begun, the joint landmarks should be carefully palpated, and the needle insertion point should be marked with ink or indented into the skin with the tip of a retracted pen.

The area should be prepared with povidone-iodine solution and then allowed to dry. The iodine can then be wiped away from the needle insertion site with an alcohol pad to prevent irritation. In patients allergic to iodine, chlorhexidine is an acceptable alternative. Once the procedure is completed, excess iodine should be removed from the skin.

Anesthesia

If desired, 1% lidocaine without epinephrine can be instilled into the skin and subcutaneous tissue over the anticipated tract of the needle; 1 mL of lidocaine is usually sufficient. As skill improves, only ethyl chloride spray for anesthesia may be used in certain cases.

Positioning

The joint to be aspirated should be resting on a hospital bed, table, or other stable, immobile structure. The patient should always be lying or sitting down and should be at a comfortable height for the physician. For details on how to position the patient for specific joint aspirations, see Approaches to Specific Joints in the Technique section. These positions are designed so that the joint capsule bulges forward towards your needle.

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.