From the Guidelines
Septic arthritis in adults should be diagnosed based on a combination of clinical, laboratory, and imaging findings, with joint fluid analysis being the definitive diagnostic method, as it allows for the identification of the causative organism and guides targeted antibiotic therapy 1. The key criteria for diagnosing septic arthritis include joint pain, swelling, warmth, and limited range of motion, typically affecting a single joint (monoarticular), with the knee being most commonly involved.
- Clinical findings:
- Joint pain and swelling
- Warmth and redness of the affected joint
- Limited range of motion
- Fever in about 50-60% of cases
- Laboratory findings:
- Elevated inflammatory markers such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR)
- Leukocytosis in peripheral blood
- Synovial white blood cell count greater than 50,000 cells/mm³ with predominance of neutrophils (>90%)
- Low glucose levels compared to serum
- Elevated protein in synovial fluid
- Imaging findings:
- Joint effusion on X-rays, ultrasound, CT, or MRI
- Associated complications such as bone erosion or abscess formation It is essential to note that if septic arthritis is in the differential diagnosis, aspiration for Gram stain and culture remains an essential part of the diagnostic evaluation, as algorithms for diagnosing gout or other conditions may not be sensitive enough to rule out septic arthritis 1. Risk factors that increase suspicion of septic arthritis include recent joint surgery, prosthetic joints, immunocompromised status, intravenous drug use, and pre-existing joint disease. Prompt diagnosis and treatment are crucial to prevent permanent joint damage, and empiric antibiotic therapy should be initiated when septic arthritis is suspected, with adjustment of therapy based on culture and sensitivity results 1.
From the Research
Criteria for Septic Arthritis in Adults
The criteria for diagnosing septic arthritis in adults include:
- Acute atraumatic joint pain, swelling, and fever 2
- Risk factors such as age older than 80 years, diabetes mellitus, rheumatoid arthritis, recent joint surgery, hip or knee prosthesis, skin infection, and immunosuppressive medication use 2
- Physical examination findings and serum markers, including erythrocyte sedimentation rate and C-reactive protein, which are helpful in the diagnosis but are nonspecific 2
- Synovial fluid studies, which are required to confirm the diagnosis 2, 3, 4, 5
- A synovial leukocyte count cutoff of >50,000 cells is often used, but this may be altered by previous administration of antibiotics 6
- In patients who have received antibiotics, a diagnostic value of >16,000 synovial leukocytes should be used to guide treatment of septic arthritis 6
- In patients who have not been given antibiotics, a diagnostic value of >33,000 synovial leukocytes yields the highest accuracy for diagnosis of septic arthritis 6
Diagnostic Considerations
- The definitive diagnosis of septic arthritis requires the direct demonstration of bacteria in synovial fluid or on positive culture of the pathogen 3
- A combination of antibiotics and the prompt removal of purulent material from the affected joint constitutes the mainstay of successful treatment 3
- The approach to periprosthetic joint infections depends on the duration of symptoms, causative organism, and individual factors 4
- Diagnostic ultrasound and arthrocentesis may aid in diagnosis 5
Treatment Considerations
- Empiric antibiotic therapy should be initiated if there is clinical concern for septic arthritis 2
- Oral antibiotics can be given in most cases because they are not inferior to intravenous therapy 2
- Total duration of therapy ranges from two to six weeks; however, certain infections require longer courses 2
- Consideration for microorganisms such as Neisseria gonorrhoeae, Borrelia burgdorferi, and fungal infections should be based on history findings and laboratory results 2