Arthrocentesis

Joint aspiration (arthrocentesis) is frequently required for diagnostic and therapeutic purposes . It may be carried out safely and virtually anywhere, i.e. on any aspect of a major peripheral joint, since the synovial cavity is a continuous one (Fig. 1) (Stone CK, Humphries R (eds), 2004) . The knee is the most common and the easiest joint for the physician to aspirate . The aspiration site, however, should be carefully selected in order to avoid important anatomical structures and cause least discomfort to the patient (Zuber TJ, 2002) . The most sensitive structures are skin and joint capsule.

Clinical scenario (Wallman P)

A 45-year old man presents to the Emergency Department one day after suffering an injury to his knee. There is no evidence of bony injury on X-ray and a diagnosis of a traumatic haemarthrosis is made on the basis of ultrasound examination (see Fig. 2). You wonder whether it is necessary to aspirate the tense haemarthrosis and whether it will benefit the patient symptomatically.

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Ultrasound examination: An echogenic haematoma (arrow) is detected behind the cartilaginous patella (cross section at the level of the patella). The cartilaginous joint surfaces are connected tightly on the intact side. A typical acoustic shadow is visible behind the femoral bone (double arrow). [Courtesy of Prof. András Palkó, Department of Radiology, University of Szeged, Hungary].

Indications for arthrocentesis

1. Need to obtain joint fluid for analysis and diagnosis
2. Drainage of post-traumatic haemarthrosis (when conservative management is unsuccessful)
3. Suspected septic arthritis
4. Intraarticular injections of local analgesics or anti-inflammatory agents

Contraindications to arthrocentesis

1. Soft tissue infection (cellulitis) overlying site of aspiration
2. Joint prosthesis
3. Coagulopathy (particularly haemophilia) or anticoagulant therapy
4. Uncooperative patient (relative contraindication)

Any unexplained joint effusion is an indication for arthrocentesis, because prompt treatment of a joint infection can preserve the joint integrity and function (Zuber TJ, 2002) . Arthrocentesis also may help distinguish between the inflammatory arthropathies and crystal arthritides or osteoarthritis. Large effusions produce swelling that require symptomatic relief. In case of post-traumatic haemarthrosis, arthrocentesis can indicate the presence of a fracture or other pathology. A history of trauma and blood or fat globules in the joint aspirate should arouse suspicion of fracture even if there is no evidence of fracture on X-ray examination

Synovial fluid analysis

1. If minimal amount of fluid is available, processing the sample is the main priority; at least partial analysis is possible on even as little as 1 ml of fluid.
2. The total volume of fluid removed should be determined.
3. Joint fluid should be assessed for colour, clarity, viscosity, mucin content (mucin clot test aka Ropes test).
4. Fluid from an acutely inflamed joint should be Gram stained (then examined under the microscope) and cultured; an examination for cell count and crystal formation should also be performed. In other cases glucose and protein levels may also be determined and compared with a simultaneously drawn blood sample; other tests can be done, if necessary (e.g. rheumatoid factor, antinuclear antibody, enzymes, etc.) (Stone CK, Humphries R (eds), 2004) .
5. The presence of fat globules (often with blood) suggests intra-articular fracture.

Complications

1. Direct needle injury to articular cartilage or local nerves – to avoid this complication, attention should be paid to anatomic landmarks and depth of needle insertion (Cardone DA, Tallia AF, 2002) .The needle should be redirected or withdrawn when severe pain is encountered during the procedure. Slow and steady movement of the needle during insertion can prevent damage to the cartilage surface from the needle bevel (Zuber TJ, 2002) .
2. Local infection at puncture site – it can be avoided by following the proper sterile technique.
3. Deep infection (i.e. iatrogenic septic arthritis)– it can be avoided by using adequate sterile technique and by not attempting to pass the needle through cellulitis (Cardone DA, Tallia AF, 2002) .
4. Rapid re-accumulation of large joint effusion after its drainage – an elastic compression dressing around the joint is advocated by some physicians to be placed immediately after large effusion drainage (Zuber TJ, 2002) .
5. Bleeding – use compression dressing and treat coagulopathy if present.

The technical aspects and details of arthrocentesis/joint injections of the shoulder, elbow, wrist, knee and ankle will be providedin:'Skills' (Joint Aspiration and Injection)

Glossary

soft tissue

In medicine, the term soft tissue refers to tissues that connect, support, or surround other structures and organs of the body. Soft tissue includes muscles, tendons, fibrous tissues, fat, blood vessels, nerves, and synovial tissues. Often soft tissue injuries are some of the most chronically painful and difficult to treat because it is very difficult to see what is going on under the skin with the soft connective tissues, fascia, joints, muscles and tendons.