How To Do Metatarsophalangeal Joint Arthrocentesis

• Diagnosis of the cause of a synovial effusion (eg, infection, crystal-induced arthritis)

• Removal of a synovial effusion and/or injection of medications as part of treatment and for pain relief

Absolute contraindications

• Infection of skin or deeper tissues at the anticipated site of needle insertion

If possible, an alternate, uninfected puncture site should be used. However, acutely inflamed joints may be generally warm, tender, and erythema, thus mimicking extra-articular infection and making it hard to find an uninvolved insertion site. Ultrasonography may be helpful; visualization of a joint effusion by ultrasonography can reinforce the decision to do arthrocentesis despite surrounding erythema. NOTE: If infectious arthritis is strongly suspected, arthrocentesis should be done regardless of erythema or negative ultrasonographic results because joint infection must not be missed.

Relative contraindications

• Severe bleeding diathesis, which may need to be corrected before arthrocentesis; routine therapeutic anticoagulation is not a contraindication, particularly if infection is suspected

Complications are uncommon and include

• Infection

• Damage to tendon, nerve, or blood vessels (traumatic tap)

• Nonsterile underpads

• For joint aspiration, a 25-mm (1-inch) 22-gauge needle and a 5-mL syringe

• Appropriate containers for collection of fluid for laboratory tests (eg, cell count, crystals, cultures)

• Enlist an assistant to provide flexion and traction to the toe.

• Sterile technique is necessary to prevent microbial contamination of both the joint space and the aspirated synovial fluid.

• A digital nerve block can be used for anesthesia.

• The aspirating needle is inserted along the dorsal portion of the joint, just medial or lateral to the extensor hallucis longus tendon.

Arthrocentesis of the metatarsophalangeal joint

Synovial fluid is withdrawn from any of the metatarsophalangeal joints. The foot and toes are flat while the patient is supine and the knee is flexed. Needle entry occurs along the dorsal portion of the joint, just medial or lateral to the extensor hallucis/digitorum longus tendon.

• Position the patient supine, with the knee flexed and the foot and toes flat on the stretcher.

• Have the patient dorsiflex the great toe. Then, in this position, palpate the dorsal aspect of the metatarsophalangeal (MTP) joint and the prominent dorsiflexed extensor tendon.

• Place a wheal of local anesthetic over the needle entry site using a 25- to 30-gauge needle.

• Have an assistant manually plantarflex (about 20°) and apply axial traction to the toe to facilitate entry of the aspirating needle into the joint space.

• Aspirate the joint using a 22-gauge needle. Enter the skin perpendicularly, at the level of the joint line, just medial or lateral to the extensor tendon. Direct the needle toward the center of the joint space. Gently pull back on the plunger as you advance. Synovial fluid will enter the syringe when the joint is entered.

• If the needle hits bone, retract almost to skin surface and then redirect the needle at a different angle.

• Drain all fluid from the joint.

• If intra-articular medications (eg, anesthetic, corticosteroid) are to be given, hold the hub of the needle motionless (using a hemostat if available) while removing the synovial fluid-containing syringe and replace it with the medication-containing syringe. If the needle has remained in place in the joint space, there will be no resistance to medication injection.

• After injecting a corticosteroid, move the joint through full range of motion to distribute the medication throughout the joint.

• Transfer synovial fluid to tubes and other transport media for synovial fluid analysis. Inspect the fluid for blood and fat.

• Apply an adhesive bandage or sterile dressing.

• Ice, elevation, and oral nonsteroidal anti-inflammatory drugs (NSAIDs) may help relieve pain.

• If an intra-articular anesthetic has been given, limited joint activity should be prescribed for 4 to 8 hours.

• If an intra-articular corticosteroid has been given, the joint should be rested for about 24 to 48 hours.

• If the patient has increased erythema, pain, and swelling > 12 hours after the procedure, the joint should be examined for possible infection.

• Carefully ensure optimal positioning before joint puncture.

• Allow adequate time for local anesthesia to take effect before proceeding.

• To avoid damaging the synovium and articular cartilage, do not advance the needle against resistance and do not move the needle once it has begun draining synovial fluid.

• If the needle tip must be relocated, first withdraw it almost to the skin surface and then redirect; do not try to change the angle of insertion while a needle is embedded in tissue.

Note also that warmth, tenderness, and erythema may overlie an acutely inflamed arthritic joint, mimicking extra-articular infection.

When trying to differentiate infectious arthritis from infection of the overlying structures (a contraindication to arthrocentesis), infectious arthritis is more likely with the following:

• Joint effusion

• Circumferential joint pain and capsule tenderness

• Pain with both gentle, passive motion and with active joint motion

When inspecting fluid, consider the following:

• The hemarthrosis of a traumatic tap tends to be nonuniformly bloody and tends to clot.

There may be no visible aspirated fluid from small joints. However, the syringe should still be used to express even a trivial drop of fluid through the needle on to a slide for microscopic evaluation. This may be sufficient to document crystal-associated arthritis or increase suspicion for infection.