Best Practices: Arthrocentesis

Arthrocentesis, the aspiration of synovial fluid (SF) from the joint space, is one of the most commonly performed procedures in the evaluation and treatment of joint diseases. Diagnostic arthrocentesis is often used to identify the etiology of acute monoarthritis. Therapeutic arthrocentesis can be used to relieve pain by evacuating a joint effusion or hemarthrosis; by draining a septic effusion; or for injection of corticosteroids, antibiotics, or anesthetic medications. The knee is the most common joint requiring arthrocentesis. This image shows arthrocentesis from the medial side of the right knee.

Frequently performed by orthopaedists and rheumatologists, arthrocentesis is also regularly utilized by primary care and emergency medicine physicians. Arthrocentesis requires a detailed understanding of joint anatomy in order to avoid injury to tendons, blood vessels, and nerves. Inserting the needle through the extensor surface of the joint, with the joint in slight flexion, will help to minimize risk. Infection of a previously sterile joint may follow arthrocentesis. An infection rate of ~1/3500 has been reported. This image depicts the basic anatomy of a joint and the synovial cavity (arrow). Image courtesy of Wikimedia Commons.

Bedside ultrasonography can help readily identify an effusion (orange arrows) and guide aspiration, especially if an alternative access site needs to be identified. An effusion will appear as an anechoic or hypoechoic collection. Lack of physician experience, difficulties with patient positioning, or body habitus can complicate arthrocentesis. While there are no absolute contraindications to arthrocentesis, relative contraindications include severe coagulopathy, severe thrombocytopenia, sepsis, associated osteomyelitis, joint prosthesis, and overlying cellulitis.

After obtaining consent, gather the needed supplies: small tray, sterile gauze, sterile gloves, drapes, surgical skin-marking pen, alcohol swab, skin antiseptic, anesthetic (1% lidocaine), small sterile syringe and 25-gauge or smaller needle for lidocaine, syringe for aspiration (may need up to 60 cc for larger joints) with 18- to 20-gauge needle, specimen tubes (EDTA for cell count and differential, lithium heparin for crystals, and a culture tube), and adhesive bandage. Because the knee joint may hold up to 70 mL of fluid, consider using a large 60-mL syringe and having an extra syringe available.

For knee arthrocentesis, position the patient comfortably in the supine position with the knee extended and palpate the joint to confirm landmarks (shown). Using sterile gloves clean the area with Betadine® (or other antiseptic solution) using circular movements, beginning at the center and working outwards. This should be repeated 3 times. A sterile drape is then positioned over the needle entry site. Some experienced practitioners utilize a "no touch" technique in which the field is not touched after antiseptic application. The parapatellar technique approaches the joint capsule from the midpoint of either the medial or lateral borders of the patella (arrow) with the needle passing between the patella and the distal femur.

After skin preparation and identification of the needle insertion site, insert a 25-gauge needle nearly parallel with the skin's surface superficially to inject a small skin wheal of anesthetic. Advance through the anesthetized skin, injecting additional anesthetic along the anticipated needle pathway (shown). A sterile drape is not required. Avoid deep injections that enter the joint space as they may alter SF analysis and culture results. Using the parapatellar technique, the aspiration needle is inserted 3-4 mm below the midpoint of either the medial or lateral borders of the patella and directed perpendicularly to the long axis of the femur and toward the intercondylar notch of the femur.

The aspiration syringe and needle are advanced into the joint space with continuous traction on the plunger until SF is obtained. Care should be taken to minimize needle motion as this may damage the articular cartilage. The maximum amount of SF possible should be aspirated, using an additional syringe if necessary. The operator can "milk" the opposite side of the joint to maximize joint decompression. When the joint has been decompressed, remove the needle, wash off any Betadine, and apply an adhesive bandage. The SF can then be transferred to the appropriate collecting tubes and culture bottles and sent to the laboratory for analysis.

Identification of an ankle effusion can be made with as little as 2 mL of fluid via bedside ultrasonography, while plain x-rays often require up to 5 mL of SF. The most sensitive location to identify an ankle joint effusion is over the anterior recess of the tibiotalar joint (shown).

Two approaches are available: anteromedial and anterolateral. The anteromedial approach is between the tibialis anterior (TA) and the medial malleolus (yellow arrow) or between the extensor hallucis longus (EHL) and the tibialis anterior (blue arrow). The anterolateral approach is between the lateral malleolus and the extensor digitorum longus (EDL) (red arrow). The anterolateral approach reduces risk to the peroneal nerve and dorsalis pedis artery.

Place the patient in a comfortable sitting position with the ankle in slight plantarflexion. Extension of the foot by the practitioner against resistance may help identify landmarks. Following usual preparation, skin cleansing, and draping, the needle is inserted in the chosen space. Inject 2-5 mL of local anesthesia such as 1% lidocaine into the subcutaneous tissue.

The aspiration needle should then be advanced posteriorly and perpendicular to the long bones (arrow) while gently aspirating until SF enters the syringe (usually 1-2 cm in an adult of average size). If bone is encountered, pull the needle back, verify the anatomic landmarks, and readvance the needle in the corrected direction.

When performing arthrocentesis of an elbow effusion (shown), the lateral approach is preferred because it avoids potential injury to the ulnar nerve. A triangle can be formed between olecranon, lateral epicondyle, and radial head. The soft depression in the center is the site for needle insertion.

Position the elbow in 90° flexion and fully pronate the forearm with palm facing downward. Prep, drape, and provide local anesthesia. Next, insert an 18-gauge needle into the depression perpendicular to both the skin and radial head from the lateral side. Advance the needle slowly toward the medial condyle while aspirating the syringe until SF is obtained. An increased risk for injury to the radial nerve and triceps tendon exists, but this approach is useful if a bulge of an effusion is palpated inferior to the lateral epicondyle.

For shoulder arthrocentesis, there are 2 approaches: anterior and posterior. To perform the anterior approach, the patient should first be sitting with shoulder slightly externally rotated. Next, palpate the coracoid process (circle) and the humeral head. As the arm is internally rotated, the joint space can be felt as a groove lateral to the coracoid process.

After prepping, draping, and anesthetizing the area, the aspiration needle is inserted medial to the head of the humerus, just below the tip of the coracoid process. It should be directed slightly laterally and superiorly to avoid arterial branches surrounding the joint capsule. The posterior approach is similar with the access site 1-2 cm inferior and medial to the posterior tip of the acromion and the needle directed anteriorly and medially toward the coracoid.

Arthrocentesis of the wrist is most often performed using a dorsal approach. The patient should rest the wrist on a table with the forearm pronated and the wrist slightly flexed. The most common needle insertion site is between the first and the second extensor tendon compartments at the radiocarpal level.

First, identify the dorsal bony prominence of the distal radius (ie, Lister tubercle) where the extensor pollicis longus turns radially toward the thumb. After prepping and draping the site and providing local anesthesia, insert the needle just distal to the Lister tubercle and ulnar to the extensor pollicis longus tendon (arrow). The needle should be directed at the soft hollow spot on the dorsum of the wrist. Slowly advance the needle while aspirating the syringe until SF is obtained. The needle should pass freely through the extra-articular tissues and a "pop" may be felt as the needle enters the joint.

SF may be classified into normal, noninflammatory, inflammatory, septic, and hemorrhagic. The gross appearance of SF can provide useful diagnostic information in terms of the degree of joint inflammation and presence of hemarthrosis. Microbiological studies of SF are the key to the confirmation of infectious conditions. Increasing joint inflammation is associated with increased SF volume, reduced viscosity, increasing turbidity and cell count, and increasing ratio of polymorphonuclear: mononuclear cells, but such changes are nonspecific and must be interpreted in the clinical setting.

The fluid should immediately be placed into proper collecting tubes. Complete analysis can usually be performed with as little as 10-15 cc of fluid. However, if only a few mL of fluid are obtained, cultures and microscopy are the most important studies. All tubes should be filled at least halfway.

No additive: Send for chemistries such as protein and glucose. Of note, serum specimens for reference should also be sent at this time.

EDTA: Used for microscopy, cell count, and differentials. EDTA prevents clotting.

Sodium heparin: Sent for crystal examination. Heparin prevents clotting and does not crystallize like EDTA.

Culture media: The remaining fluid (ideally at least 5 cc) should be sent for culture.

In gout, monosodium urate crystals appear as needle-shaped intracellular and extracellular crystals. When examined with a polarizing filter, they appear yellow when aligned parallel to the axis of the red compensator, but they turn blue when aligned across the direction of polarization (shown). Image courtesy of Wikimedia Commons.

A prior history of gout or pseudogout does not rule out the possibility of acute septic arthritis. In fact, the latter is more common in patients with a history of crystal-induced arthritis. Septic arthritis must be diagnosed and treated promptly. Irreversible damage can occur within 4-6 hours, and the joint can be completely destroyed within 24-48 hours (shown).

After the procedure, the area should be cleaned with any remaining antiseptic and a dry sterile dressing or adhesive bandaging should be applied to the wound. Nonsteroidal anti-inflammatory analgesics may be used for pain control. The joint should be rested and the patient should be instructed to look for signs of local infection including erythema, warmth, swelling, or systemic signs such as fevers and chills. If corticosteroids are injected, a postinjection flare may occur in up to 20% of patients. This usually subsides within 48 hours, which helps differentiate it from infection. A significant increase in pain and swelling can also occur if a large hematoma develops. Patients should report these symptoms to their doctors.

More Best Practices

• Best Approaches to Rapid Infusion With Intraosseous (IO) Access
• Best Approaches to Rapid Infusion With Intraosseous (IO) Access
• Best Practices: Emergency Airway Management
• Best Practices: Regional Blocks
• Thoracentesis Best Practices
• Other Slideshows

For more information, see the following resources:

• Medscape Reference: Ankle Arthrocentesis
• Medscape Reference: Arthrocentesis, Wrist
• Medscape Reference: Aspiration Techniques and Indications for Surgery, Septic Arthritis
• Medscape Reference: Bedside Ultrasonography, Joint Assessment
• Medscape Reference: Elbow Arthrocentesis
• Medscape Reference: Knee Arthrocentesis

For more information, see the following resources:

• Medscape Reference: Shoulder Arthrocentesis

Contributor Information

Author
Mark P. Brady, PA-C
Chief Physician Assistant
Department of Emergency Medicine
Cambridge Hospital
Cambridge Health Alliance
Cambridge, Massachusetts

Disclosure: Mark P. Brady, PA-C, has disclosed no relevant financial relationships.

Editor
Lars Grimm, MD, MHS
House Staff
Department of Diagnostic Radiology
Duke University Medical Center
Durham, North Carolina

Disclosure: Lars Grimm, MD, MHS, has disclosed no relevant financial relationships.

Contributor Information

Reviewers
B. Sonny Bal, MD
Associate Professor
Department of Orthopedic Surgery
University of Missouri School of Medicine
Columbia, Missouri

Disclosure: B. Sonny Bal, MD, has disclosed no relevant financial relationships.

Richard S. Krause, MD
Senior Faculty
Department of Emergency Medicine
State University of New York at Buffalo School of Medicine
Buffalo, New York

Disclosure: Richard S. Krause, MD, has disclosed no relevant financial relationships.