1. 
   

   What are the indications for arthrocentesis?

   
   
2. 
   

   When do you need to reverse a coagulopathy?

   
   
3. 
   

   What is the best site to reduce the likelihood of complications?

   
   
4. 
   

   What are the diagnostic criteria for a septic effusion?

   
   

   For gout?

In the hospital setting, arthrocentesis is usually performed to diagnose whether a patient has a septic joint and to narrow antibiotic therapy once the cultures are known. Although bacterial infections may affect less than 20% of all cases of acute arthritis, failure to diagnose bacterial infection may lead to permanent cartilage damage, destruction of bone, loss of joint function, and, in extreme cases, loss of limb and death. Aspiration almost always yields a diagnosis, and in the case of the septic joint, is akin to draining an abscess. Luckily, in the vast majority of cases, aspirating a joint is a simple and safe procedure rarely complicated by infection. This chapter reviews a number of key elements related to arthrocentesis, including the indications and contraindications, procedure set-up and insertion techniques, and testing.

In the vast majority of cases, septic joints are a result of hematogenous seeding. Inflamed and artificial joints have an increased risk of being seeded by bacteria. The vasculature of the synovium does not have a basement membrane, thereby allowing bacteria to enter the joint space. Direct trauma to the joint such as an animal bite is a much rarer cause of joint infection. Polyarticular involvement is uncommon, but is sometimes seen in patients with rheumatoid arthritis. Other risk factors for septic arthritis include age older than 80, immunosuppression, sexually transmitted diseases, diabetes mellitus, and HIV infection. Bacterial arthritis is most often caused by typical gram-positive bacteria, but there is an increasing incidence of gram-negative septic arthritis. Gonococcal arthritis remains the most common cause of bacterial arthritis in sexually active adults.

Crystal-induced arthritis, gout, and pseudogout may mimic septic arthritis, and may coexist with septic arthritis. They are an under-recognized cause of postoperative fever. Pseudogout is caused by the deposition of calcium pyrophosphate in the joint milieu resulting in an inflammatory response. Risk factors for pseudogout include older age, diabetes, hypothyroidism, hemochromatosis, abnormalities of calcium homeostasis, and endstage renal disease. Patients often have normal calcium levels despite the presence of pseudogout. Gout or monosodium urate–induced arthritis is caused by an inflammatory reaction to monosodium urate deposition in synovial tissue, bursae, and tendon sheaths. Gouty attacks occur when urate crystals are released from preexisting tissue deposits. Risk factors for gout include hyperuricemia; postmenopausal state, especially for those women taking thiazide diuretics; chronic renal insufficiency; immunosuppressives, such as cyclosporine; and sickle cell and other hematologic disease. Nevertheless, the factors responsible for the development of gout are not well understood. Although hyperuricemia is associated with an increased risk of gout and the higher the level the greater the risk, levels do not correlate with severity of disease. An acute elevation of uric acid as seen in the tumor lysis syndrome does not usually provoke gouty attacks, and gout is less common in endstage renal disease and rheumatoid arthritis than expected. In addition, the presence of urate crystals in synovial fluid is not always sufficient to produce an attack and many people have asymptomatic chronic hyperuricemia. Serum urate levels at the time of an acute gouty attack may in fact be in the normal range for the general population in as many as 40% of affected patients.

Excluding cases of trauma, pain with passive motion of a joint or palpation of the joint capsule suggests synovitis and requires further investigation.

A diagnostic arthrocentesis is indicated for patients with acute articular or periarticular pain and risk factors (Table 118-1). Patients with a sudden increase in pain in a previously damaged joint may have a bacterial infection but not necessarily have prodromal symptoms or fever. Fever may not be associated with bacterial infection in greater than 40% of patients and fever may be associated with other conditions that cause joint pain, including gout, especially when polyarticular. Hence, synovial fluid analysis is required to exclude the diagnosis.

Although radiography is essential in the diagnosis of trauma, it has no role in the early diagnosis of a joint infection. Neither CT or MRI or radionuclide scanning can distinguish between septic and noninfectious causes of inflammatory synovitis. Imaging is indicated, however, in the following patients with suspected

• Sternoclavicular joint infection: to look for mediastinal extension
  
• Sacroiliac joint infection: to look for pelvic involvement
  
• Osteomyelitis.

Arthrocentesis or aspiration of tophi is needed to establish the diagnosis of crystal deposition disease and to distinguish between pseudogout and gout. Arthrocentesis should be performed before initiating chronic hypouricemic therapy indicated for gout but not for pseudogout.