Although arthrocentesis can be performed by experienced clinicians using clinical landmarks, aspiration and injection of deeper joints (hip), complicated joints (wrist), and even large joints such as the knee and shoulder can be performed with far greater accuracy utilizing ultrasound guidance. Some joint aspirations are shown on Plate 5-13. The knee is probably easiest to aspirate because simply positioning the needle beneath the patella suggests that it has penetrated the joint, but this is not ensured without fluid return or visualization of the needle position using ultrasound or alternative imaging.

The joint aspirated should be one that is symptomatic and swollen. The area is cleaned, and the site for needle puncture marked on the skin; this can be done with the wooden tip of a cotton swab. The skin and deeper tissue is infiltrated with a solution of 1% lidocaine for anesthesia. The aspiration needle should be at of least 20 gauge (22-gauge needles may be needed for finger or toe joints) to avoid plugging of the orifice with fat or other soft tissue.

Universal safety precautions should be practiced. One hand is used to identify the anatomic landmarks, with care not to touch the actual site. The initial thrust should be decisive; if fluid is not readily obtained, the position of the needle can be readjusted a little without withdrawing it. A small amount of fluid can be obtained from almost any joint. Only 1 mL of fluid is required for a thorough synovial fluid analysis, but more fluid may be removed, if needed, to relieve symptoms in a distended joint. Even a drop of fluid in the hub of the aspirating needle can allow identification of crystals or infectious agents (if seen on Gram stain), and an estimate of the white blood cell count.

The same procedure is used for intra-articular injections of depot corticosteroids. This treatment may provide temporary relief for some patients with osteoarthritis and more marked relief in patients with crystal-associated and other inflammatory arthritis. Synovial fluid should always be examined as part of the injection procedure and injection avoided if there is any suspicion of joint infection.

Based on the clinical signs and the symptoms reported by the patient, the specific tests and stains needed are determined before aspiration (see Plates 5-14 and 5-15). If infection is suspected, some fluid should be promptly delivered to the laboratory for culture.

Complications from joint aspiration/injection are extremely rare. To help avoid infection, the route of aspiration should not be through areas of cutaneous infection or a rash like psoriasis. Hemarthrosis resulting from a traumatic arthrocentesis (“bloody tap”) is a rare complication, and aspiration can be done even in patients being treated with anticoagulants. No special care is needed after the procedure, but rest for 1 to 2 days may increase the efficacy of injected corticosteroids.