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Septic arthritis
Essentials
- 1
Early diagnosis and treatment are critical for the prevention of irreversible joint destruction.
- 2
Diagnosis is based on clinical features and synovial fluid examination; imaging techniques have a role in difficult cases.
- 3
Staphylococcus aureus, Streptococcus and Neisseria gonorrhoeae are the most frequent pathogens in adults and older children. Methicillin-resistant staphylococcus aureus (MRSA) is an emerging problem, particularly among intravenous drug users. Fungal, mixed bacterial and exotic organisms are rarely seen outside of the intravenous drug using population.
- 4
Successful treatment hinges on rapid and complete joint lavage and high-dose parenteral antibiotics guided by culture results.
- 5
Outcomes are good in paediatric and gonococcal subgroups, but the presence of chronic arthritis or polyarticular involvement is associated with up to 15% mortality and 50% chronic joint morbidity.
Introduction
Septic arthritis is defined as bacterial infection of the synovial space. The knee is the most commonly affected joint in adults and the hip joint in the paediatric age group. Intravenous drug users have a predisposition toward axial joint infections. Septic arthritis is commonly monoarticular and monomicrobial.
Aetiology, pathogenesis and pathology
Septic arthritis occurs as a consequence of a number of pathological processes: inoculation resulting from a penetrating injury or procedure, direct spread from an adjacent infective process such as osteomyelitis, cellulitis, bony or soft tissue abscess. Most commonly it may result from haematogenous spread, as in sepsis or as a consequence of endocarditis. Once a joint is inoculated, an acute inflammatory reaction with hypersecretion of synovial serous or seropurulent exudate occurs. As the infection progresses, articular cartilage is eroded both through direct bacterial enzymatic destruction and as a consequence of the release by inflammatory and synovial cells of proteolytic enzymes. If the inflammation is not treated, loss of articular cartilage fluid eventually leads to healing by bony ankylosis or joint fibrosis. Co-morbidity or deficient host defences are risk factors for infection and can be associated with more rapid and severe disease ( Table 9.3.1 ).
Table 9.3.1
Risk factors for septic arthritis
| Risk factors | Examples |
|---|---|
| Direct penetration | Trauma Medical (surgery, arthrocentesis), intravenous drug use |
| Joint disease | Chronic arthritis |
| Host immune deficit | Glucocorticoid or immunosuppressive therapy HIV infection Chronic illness Cancer |
The majority of cases are community acquired and occur in children and young adults. Prosthetic joint surgery and the invasive management of chronic arthritis are factors in the increased prevalence observed in older age groups.
Epidemiology
The incidence of proven and probable septic arthritis in Western Europe is 4 to 10 per 100,000 patients per year. This is more prevalent in lower socioeconomic groups in both Northern Europe and Australia.
The prevalence is 29 cases per 100,000 in the indigenous population, with a relative risk of 6.6 compared with the European Northern Territory Australian population.
The incidence of septic arthritis is increasing and is linked to an increase in orthopaedic-related infection, an ageing population, more invasive procedures being undertaken and an enhanced use of immunosuppressive treatment.
Clinical features
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