Knee Arthrocentesis

Knee Arthrocentesis or joint aspiration is a procedure whereby a sterile needle and syringe are used to drain joint fluid from the knee joint.

Indications

1. Diagnostic

• Removal of fluid for culture if suspicious of septic joint.
• Removal of fluid if suspicious of hemarthrosis or traumatic joint injury.

2. Therapeutic

• Relief of discomfort caused by intra articular pressure and distension of joint capsule and ligaments by accumulating fluid.
• Drainage of pus to decrease damaging effects of bacteria, WBCs and inflammatory response on joint space.
• Injection of medications such as glucocorticoids ( one of the modalities of treatment in non infectious inflammatory arthritis such as juvenile rheumatoid arthritis )

Contraindications

• Hemophilia
• Overlying skin infection or cellulitis
• Bacteremia
• Anatomic inaccessibility

Materials required for Procedure
Sterile drapes, Sterile gloves, 3 povidone-iodine swabs, sterile 2×2 gauze squares, 25-gauge 1.5 inch needle ( to administer lidocaine ), 21-gauge 1.5 in ch needle ( to draw up lidocaine ) , 18-gauge 1.5 inch needle ( to enter joint capsule ), 5-10 or 20 ml syringes 9 (depending on the size of effusion), 1% lidocaine, sterile container for joint fluid, hemostat, adhesive bandage.

Procedure
The knee joint is the most easily aspirated joint. Other joints that may need aspiration should be evaluated by examiners with more experience ( e.g orthopedic specialists ) to avoid damage to cartilage and growth plates.

1. Locate landmarks as part of a careful physical exam, with child’s knee in full extension. Palpate the posterior edge of the patella medially or laterally. The patella should be easily mobile and the quadriceps muscle relaxed to ensure easy aspiration.

2. There are two approaches as follows:

Medial ( rheumatologic ) approach: Preferred with small effusions. Target area is under the mid point of the patella. Remember to allow 1-2 cm posterior to the medial edge of the patella to avoid the gliding surface.

Lateral ( Orthopedic ) approach: Easier with large effusion. Target area is directly into the center of the bulging suprapatellar pouch, at the level of the cephalad border of the patella.

3. If needed conscious sedation may be administered at this time.

4. Clean the knee liberally with povidone-iodine, including the medial and lateral aspects of the joint over the patella ( > 180 degrees )

5. Prepare and drape the joint in a sterile fashion.

6. Anesthetize the aspiration site and subcutaneous tissue with 1% lidocaine using the 25-gauge, 1.5 inch needle. Lidocaine may be mixed with sodium bicarbonate at a ratio of 9ml lidocaine to 1ml bicarbonate to minimize stinging.

7. Approach will be medial or lateral with an 18-gauge, 1.5 inch needle attached to a 10 ml or 20 ml syringe.

8. Aspiration of joint fluid confirms correct placement. Pressure on the opposite side of the injection may enhance the suprapatellar pouch, ant thus facilitate removal of fluid when using the lateral approach. With the medial approach, squeezing the pouch may facilitate fluid flow.

9. Remove only as much fluid as flows freely.

10. Remove the needle, use sterile 2×2 gauze squares to cover injection site and apply gentle pressure.

11. Cover the injection site with an adhesive bandage and remove excess povidone-iodine.

12. Send joint fluid to the laboratory for analysis.

Complications

• Infection
• Bleeding
• Damage to the articular cartilage