1 Removal of a joint effusion causing severe pain and distension that limits function To obtain joint fluid for the diagnosis of arthritis Complications Bleeding Infection, joint space or bone Contraindications (Relative) Bleeding diathesis Patients with bleeding diatheses (i.e., hemophilia) as the cause of the joint effusion usually require only immobilization and replacement of coagulation factors Presence of a fracture around the joint space Aspiration may increase the chance of infection when a fracture is present Equipment Marking pen, antiseptic solution, gauze, bacteriostatic saline solution, adhesive bandage Local anesthetic 1% lidocaine, topical anesthetic such as 4% lidocaine cream 25- or 27-gauge needle, 3-mL syringe, 18- or 20-gauge needle, and 5- to 10mL syringe, specimen collection tubes with patient labels Knee Joint Procedure The knee is the joint that most commonly requires aspiration in children, primarily to evaluate for possible bacterial infection or Lyme disease Radiographs should be obtained before aspirating the joint, and ultrasound may also be useful to document the presence of an effusion if not obvious on radiographs Place the child supine on the examination table, and completely extend the knee if possible Pain may prevent full extension If so, a towel roll placed under the slightly flexed joint may be helpful for comfort and in stabilizing the position Restrain the child as necessary Have an assistant hold both the thigh and calf of the involved leg Consider pharmacologic sedation as necessary Consider applying topical 4% lidocaine or other anesthetic cream 30 to 45 minutes prior to the procedure The lateral approach to the knee is preferred because it avoids passage through the vastus medialis muscle Pick a puncture point at the midpatellar level in the anteroposterior view and at the posterior margin of the patella in the lateral view ( Fig 130.44 )