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  • • Diagnostic: Sampling of fluid for laboratory evaluation (eg, septic joint, inflammatory arthritis).

    • Therapeutic.

    • • Injection of corticosteroids.

      • Injection of local anesthetic.

      • Removal of hemarthrosis for pain relief following trauma.



  • • Skin or soft tissue infection (eg, cellulitis, septic bursitis) because there is an increased risk of causing a septic joint.

    • Corticosteroid injection into a known or suspected septic joint.


  • • Coagulopathy. The procedure may result in hemarthrosis, but one needs to weigh the risk against the need to diagnose a septic joint.

    • Bacteremia, because of the increased risk of causing septic joint.


  • • Syringes (20 mL for knee; 10 mL for ankle).

    • 21–25-gauge needles; they must be long enough to enter joint.

    • Sterile collection container.

    • Povidone-iodine and alcohol for sterile preparation of skin.

    • Sterile gloves.

    • 4 × 4 gauze.

    • Ethyl chloride (optional).

    • Lidocaine (optional).


  • • Infection occurs in < 1/10,000 when performed under sterile conditions.

    • Bleeding into joint is exceedingly rare, even in patients who are taking anticoagulant medication.

    • If corticosteroids are being injected, there is a risk of skin discoloration and fat atrophy following the procedure.

Pearls and Tips

  • • Do not make an ink mark directly over injection/aspiration site because it will enter the joint when the needle passes through it.

    • Instead, use the wood end of a sterile cotton swab or another round object to make an indentation in the skin prior to cleaning with povidone-iodine.

    • If infection is a concern, a larger bore needle (18 gauge or 19 gauge) may be needed to aspirate because sometimes purulent fluid will not be drawn into a smaller needle.

    • Do not overtighten the needle on to the syringe, and check to make sure the needle easily twists off the syringe before starting the procedure.

    • This allows you to empty a full syringe and reattach it without ever pulling the needle out of the joint.

    • Lidocaine can be used to numb the skin prior to aspiration/injection, but it can distort anatomic landmarks.

    • Alternatively, a topical agent such as ethyl chloride can be used.

Patient Positioning

  • • Have the patient lie supine on the examination table.

    • Place the table at a comfortable height for you and sit or stand at the affected side of the patient.

Anatomy Review

  • • The distal femur articulates with the proximal tibia to make up the knee joint.

    • The patella sits in a groove anterior to the joint.


Knee in Extension

  • • With the knee extended, have the patient relax the quadriceps.


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