Ankle Arthrocentesis 

Arthrocentesis (synovial fluid aspiration) can be performed diagnostically (for identification of the etiology of acute arthritis) or therapeutically (for pain relief, drainage of septic effusion, or injection of medications).^{[1, 2]} The clinician performing the procedure should be familiar with the anatomy of the specific joint in order to avoid puncture of tendons, blood vessels, and nerves.^[3] Using the extensor surface of the joint for needle insertion, while keeping the joint in minimal flexion, minimizes the risk of such injuries.

See the images below.

Diagnostic

• Evaluation of monoarticular arthritis^[4]
• Evaluation of suspected septic arthritis^[5]
• Evaluation of joint effusion
• Identification of intra-articular fracture and ligamentous tear
• Identification of crystal arthropathy^[6]

Therapeutic

• Relief of pain by aspirating effusion or blood
• Injection of medications^[7] (eg, corticosteroids, antibiotics, anesthetics)
• Drainage of septic effusion

Absolute

• None

Relative

• Suspected septic joint (In this case, no contraindications exist.)
• Cellulitis overlying the joint (If arthrocentesis is performed, the patient should be admitted for intravenous antibiotics, even if the synovial fluid is not suspicious for infectious arthritis.)
• Skin lesion or dermatitis overlying the joint
• Known bacteremia
• Adjacent osteomyelitis
• Uncontrolled coagulopathy
• Joint prosthesis (A joint prosthesis is preferably tapped by an orthopedist.)

Patients who are anxious, in severe pain, or unable to cooperate with the procedure might require procedural sedation and analgesia. For more information, see Procedural Sedation.

Local anesthesia is warranted. After skin preparation, draping, and identification of the needle insertion site, use a 25- or 27-gauge (ga) needle to inject 2-5 mL of local anesthetic (eg, lidocaine 1%) into the subcutaneous tissue. For more information, see Local Anesthetic Agents, Infiltrative Administration.

See image below.

Deep injections that might enter the joint space are not recommended because they may alter the synovial fluid analysis results.

• Sterile gloves and drapes
• Gauze pads, 4 x 4 inch, 5
• Skin preparatory solution
• Lidocaine 1%
• Syringe, 5 mL
• Needles, 18 ga and 25 or 27 ga
• Syringes, 20 mL, 30 mL, 60 mL
• Needle, 18 ga or 20 ga (A patient who is morbidly obese might require a 21-ga spinal needle for arthrocentesis.)
• Hemostat
• Specimen tubes
• Bandage

• The patient should be placed either sitting or supine on a stretcher, with the knee flexed at 90 º and the leg either hanging from the side of the stretcher or bent with the heel resting against the stretcher.
• Plantar flexion of the ankle against minimal ankle dorsiflexion by the patient helps define the anatomy.

Prepare and drape the skin, and allow drying.

Using a sterile technique, attach the 18- or 20-ga needle to the 20-mL syringe and pull the plunger to break resistance.

While stretching the skin over the insertion site (see below for choices of insertion site), insert the needle into the joint space while gently aspirating until synovial fluid enters the syringe (usually 1-2 cm in an adult of average size).

If a bone is encountered, pull the needle back, verify the anatomical landmarks, and re-advance the needle in a corrected direction.

If removal of more fluid is desired, a hemostat flush to the skin can be used to secure the needle in place while the syringe is replaced with a new one.

Remove the needle and apply a bandage.

Divide the aspirated synovial fluid into the different specimen containers.

Anterolateral approach (preferred)

This is the preferred approach for ankle joint aspiration because it avoids potential injury to the dorsalis pedis vessels or the deep peroneal nerve, which course through the medial aspect of the foot.

Identify the ankle joint line, the lateral malleolus, and the lateral border of the extensor digitorum longus.

Extension of the foot against the patient’s resistance or active flexion/extension movement by the patient helps the practitioner identify the space between the base of the lateral malleolus and the lateral border of the extensor digitorum longus.

Insert a needle (18-20 ga) at the joint line midway between the base of the lateral malleolus and the lateral border of the extensor digitorum longus, advancing the needle perpendicular to the fibular shaft.

Anteromedial approach

Exercise care with this approach to avoid injury to both the dorsalis pedis vessels and the deep peroneal nerves that are immediately below and lateral to the extensor hallucis longus tendon.

Identify the ankle joint line, the medial malleolus, and the tendons of the extensor hallucis longus and the tibialis anterior.

Extension of the foot against the patient’s resistance or active flexion/extension movement by the patient helps the practitioner identify the space between the medial border of the extensor hallucis longus and the lateral border of the tibialis anterior or between the base of the medial malleolus and the medial border of tibialis longus.

See the image below.

Insert a needle (18-20 ga) at either insertion point and advance the needle perpendicular to the tibial shaft.

See the image below.

• The anterolateral approach is preferred for ankle joint aspiration because it avoids potential injury to the dorsalis pedis vessels or the deep peroneal nerve, which course through the medial aspect of the foot.

• Improper needle placement, a small amount of effusion, mechanical obstruction of the needle against cartilage, or thickened synovium can result in a dry tap.
• Potential damage to cartilage can be avoided by understanding of the joint anatomy and avoiding further advancement of the needle into the joint space once synovial effusion enters the syringe.
• Most hemarthroses are small and self-limited and only require observation. Hemarthrosis in coagulopathic patients requires correction of the coagulopathy in consultation with a hematologist.
• Proper skin cleansing and use of aseptic technique minimizes the risk of introducing infection into a sterile joint to less than 1:10,000.
• When performing arthrocentesis through infected skin for the diagnosis of a potentially septic joint, intravenous antibiotics should be given immediately following the procedure, and the patient should be admitted for continuation of the antibiotics.

Table. Synovial Fluid Analysis in Different Diseases^[8] (Open Table in a new window)

Operative characteristics of septic joint effusion findings

• Total WBC >25,000/mL (sensitivity, 77%; specificity, 73%; positive likelihood ratio (LR+), 29; negative likelihood ratio (LR-), 0.71)
• Total WBC >50,000/mL (sensitivity, 62%; specificity, 92%; LR+, 7.7; LR-, 0.42)^[9]
• Total WBC >100,000/mL (sensitivity, 22%; specificity, 99%; LR+, 2.9; LR-, 0.32)
• PMN cells ≥ 90% (sensitivity, 73%; specificity, 79%; LR+, 3.4; LR-, 0.34)
• Synovial glucose or serum glucose concentration < 0.5 (sensitivity, 51%; specificity, 85%; LR+, 3.4; LR-, 0.58)
• Protein concentration >3 g/dL (sensitivity, 48%; specificity, 46%; LR+, 0.9; LR-, 1.1)
• Lactic dehydrogenase (LDH) concentration >250 U/L (sensitivity, 100%; specificity, 51%; LR+, 1.9; LR-, 0.1)