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INTRODUCTION

Excluding cases of trauma, pain with passive motion of a joint or palpation of the joint capsule suggests synovitis and requires further investigation. 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 (Figure 127-1). 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 patients with suspected:

Figure 127-1

Practice algorithm: Diagnostic arthocentesis.

  • Sternoclavicular joint infection: to look for mediastinal extension.

  • Sacroiliac joint infection: to look for pelvic involvement.

  • Osteomyelitis.

See Figure 193-4, approach to the patient with suspected septic arthritis.

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. 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 (see Chapter 193 [Osteomyelitis and Septic Arthritis] and Chapter 194 [Prosthetic Joint Infections]).

Arthrocentesis or aspiration of tophi is needed to establish the diagnosis of crystal deposition disease and to distinguish between pseudogout and gout. Classic radiographic findings of gout occur only very late in the disease. Likewise, radiographic findings of chondrocalcinosis and cystic erosions without marked joint space narrowing may suggest pseudogout but cannot confirm that the patient's sudden increase in pain is caused by this disease and not by coexisting bacterial infection. Arthrocentesis should be performed before initiating chronic hypouricemic therapy indicated for gout but not for pseudogout. Luckily, in the vast majority of cases, aspirating a joint is a simple and safe procedure rarely complicated by infection (see Chapter 247 [Gout, Pseudogout, and Osteoarthritis]). See Tables 127-1,127-2, 127-3, 127-4.

Table 127-1Basic Consideration

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