- 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.
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. |Favorite Table|Download (.pdf)
Table 47–1. Risk Factors and Mechanisms of Infection in Bacterial Arthritis.
|Risk Factor||Mechanism of Infection||Comments|
|Rheumatoid arthritis (RA)|
- Local and systemic factors play a role
- Damaged joint serves as nidus for infection
- Immunosuppressive medications predispose to infection, especially previous use of oral or intra-articular glucocorticoids
- RA is complicated by septic arthritis in 0.3–3% of patients
- Polyarticular septic arthritis in RA has >50% mortality rate
- Staphylococcus aureus most likely organism
- Foreign body serves as nidus for infection, especially for pathogens that lay down biofilms or glycocalyx layer (eg, Staphylococcus epidermidis)
- No microvasculature in artificial joint
- Rates of infection have decreased over the past 30 years
- Higher incidence in revision arthroplasty (see text for details)
|Injection drug use; indwelling lines; chronic skin infections|
- Recurrent bacteremia with subsequent hematogenous seeding of joints
- Patients receiving long-term hemodialysis, with chronic indwelling lines, with repeated skin injections (eg, insulin), or with chronic skin infections are susceptible
- The knee is the most commonly infected joint in injection drug users, but also see axial joint infections, including sternoclavicular and sacroiliac joint involvement
- S aureus (often methicillin-resistant) most common cause in injection drug users
- Pseudomonas aeruginosa seen in ∼10% of cases
|Crystal-induced arthritis (gout, pseudogout)|
- Local factors
- Joint damage from crystals
- Synovial fluid acidosis in crystal-induced synovitis promotes cartilage damage
- Crystal-induced arthritis can cause high synovial WBC counts without infection
- Presence of crystals does not rule out infection
- Infection-mediated destruction of articular cartilage can rarely ...
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