Arthrocentesis is performed for diagnostic and therapeutic purposes. The main indication for arthrocentesis is to assist in the evaluation of arthritis of unknown cause. In the intensive care unit, it is most commonly performed to rule out septic arthritis. As many types of inflammatory arthritis mimic septic arthritis, synovial fluid analysis is essential in differentiating the various causes of inflammatory arthritis [4,7] (Table 19.1). Therefore, patients presenting with acute monoarthritis or oligoarthritis require prompt arthrocentesis with subsequent synovial fluid analysis, preferably before initiation of treatment.

Arthrocentesis is also used for therapeutic purposes. In a septic joint, serial joint aspirations are required to remove accumulated inflammatory or purulent fluid. This accomplishes complete drainage of a closed space and allows serial monitoring of the total white blood cell count, Gram stain, and culture to assess treatment response. Inflammatory fluid contains many destructive enzymes that contribute to cartilage and bony degradation; removal of the fluid may slow this destructive process [8,9]. Additionally, arthrocentesis allows for injection of long-acting corticosteroid preparations into the joint space, which may be a useful treatment for various inflammatory and noninflammatory forms of arthritis [10].

Before performing arthrocentesis, it must be ascertained that the true joint is inflamed and an effusion is present. This requires a meticulous physical examination to differentiate arthritis from periarticular inflammation. Bursitis, tendinitis, and cellulitis all may mimic arthritis. In the knee, the examination begins with assessment of swelling. A true effusion may cause bulging of the parapatellar gutters and the suprapatellar pouch [11]. The swelling should be confined to the joint space. To check for small effusions, the bulge test is performed [12]. Fluid is stroked from the medial joint line into the suprapatellar pouch and then from the suprapatellar pouch down along the lateral joint line. If a bulge of fluid is noted at the medial joint line, a small effusion is present (Fig. 19.1). If a large effusion is present, one can detect a ballotable patella by pushing it against the femur with the right index finger while applying pressure to the suprapatellar pouch with the left hand [13]. Comparison with the opposite joint is helpful. Many texts describe joint examination and assessment for fluid in the knee and other joints [11,12,13].

Absolute contraindications to arthrocentesis include local infection of the overlying skin or other periarticular structures and severe coagulopathy [1,2,3,10]. If coagulopathy is present and septic arthritis is suspected, every effort should be made to correct the coagulopathy (with fresh-frozen plasma or alternate factors) before joint aspiration. Therapeutic anticoagulation is not an absolute contraindication, but every effort should be made to avoid excessive trauma during aspiration in this circumstance. Known bacteremia is a contraindication because inserting a needle into the joint space disrupts capillary integrity, allowing joint space seeding [14]. However, if septic arthritis is strongly suspected, joint aspiration is indicated. The presence of articular instability (e.g., that seen with badly damaged joints) is a relative contraindication, although the presence of a large presumed inflammatory fluid may still warrant joint aspiration.

The major complications of arthrocentesis are iatrogenically induced infection and bleeding, both of which are extremely rare [1]. The risk of infection after arthrocentesis has been estimated to be less than 1 in 10,000 [15]. Hollander [16] reported an incidence of less than 0.005% in 400,000 injections. Strict adherence to aseptic technique reduces the risk of postarthrocentesis infection. Significant hemorrhage is also extremely rare. Correction of prominent coagulopathy before arthrocentesis reduces this risk.

Another potential complication of arthrocentesis is direct injury to the articular cartilage by the needle. This is not quantifiable, but any injury to the cartilage could be associated with degenerative change over time. To avoid cartilaginous damage, the needle should be pushed in only as far as necessary to obtain fluid and excessive movement of the needle during the procedure should be avoided.

Other complications include discomfort from the procedure itself, allergic reactions to the skin preparation or local anesthetic, and in the case of steroid injection, postinjection flare and local soft-tissue atrophy from the glucocorticoid [17].

Joint aspiration is easily learned. A sound knowledge of the joint anatomy, including the bony and soft-tissue landmarks used for joint entry, is needed. Strict aseptic technique must be followed to minimize risk of infection, and relaxation of the muscles surrounding the joint should be encouraged because muscular contraction can impede the needle’s entry into the joint.

Most physicians in the intensive care unit can aspirate the knee because it is one of the most accessible joints. Other joints should probably be aspirated by an appropriate specialist, such as a rheumatologist or an orthopedic surgeon. Certain joints are quite difficult to enter blindly and are more appropriately entered using radiologic guidance, such as with fluoroscopy or computed tomography; these include the hip, sacroiliac, and temporomandibular joints. Many texts describe in detail the aspiration technique of other joints [3,16,17,18]. The technique for knee aspiration is as follows: