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Essentials of Diagnosis

  • The classic presentation is acute onset of painful, warm, and swollen joint, usually monoarticular and affecting large weight-bearing joints.
  • Synovial fluid white blood cell counts usually >50,000 cells/mcL with over 80% neutrophils.
  • Positive synovial fluid culture.
  • Staphylococcus aureus is the most common cause of septic arthritis in native joints.

General Considerations

The reported incidence of septic arthritis varies from 2–10 per 100,000 per year in the general population, with substantially higher rates in patients with rheumatoid arthritis (RA) or joint prostheses (both ∼30–70 cases per 100,000 per year). The incidence of bacterial arthritis is significantly higher among children than adults.

Septic (bacterial) arthritis is a medical emergency, and delay in diagnosis and treatment can lead to irreversible joint destruction and an increase in mortality. Even with the advent of better antimicrobial agents and techniques of joint incision and drainage, the rate of permanent joint damage from septic arthritis is 25–50%. The case fatality rate for monoarticular bacterial arthritis also remains high at 11%, with increased mortality rates seen in the setting of polyarticular septic arthritis (as high as 50%), underlying RA, and in immunocompromised states. Risk factors for the development of bacterial arthritis include chronic arthritic syndromes, prosthetic joints, parenteral drug use, extremes of age, diabetes mellitus, and immunocompromised conditions (Table 47–1).

Table 47–1. Risk Factors and Mechanisms of Infection in Bacterial Arthritis.

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