From the Research
The antibiotic of choice for septic arthritis of the knee is typically vancomycin, with the final selection depending on the suspected pathogen and local resistance patterns. For empiric therapy before culture results are available, intravenous vancomycin (15-20 mg/kg every 8-12 hours) is often started to cover methicillin-resistant Staphylococcus aureus (MRSA), while ceftriaxone (1-2g daily) may be added to cover gram-negative organisms 1. Once the causative organism is identified through joint fluid culture, therapy should be narrowed to the most effective antibiotic.
Key Considerations
- Treatment duration typically ranges from 2-4 weeks of intravenous antibiotics, potentially followed by oral antibiotics depending on clinical response.
- Alongside antibiotic therapy, surgical drainage of the joint is usually necessary, which can be achieved through arthrotomy or arthroscopy with thorough irrigation and debridement of all infected tissue 1.
- The Gächter classification can be useful in establishing a prognosis or determining the need for extensive debridement 1.
- Prompt treatment is essential to prevent cartilage destruction, which can begin within 48 hours of infection onset.
Pathogen Considerations
- Staphylococcus aureus is the most common pathogen in adults, and the knee joint's relatively avascular environment makes it difficult for antibiotics alone to eradicate infection.
- MRSA septic arthritis tends to affect older patients with multiple comorbidities and has a higher mortality rate compared to methicillin-sensitive Staphylococcus aureus (MSSA) septic arthritis 2, 3.
- Empirical antibiotic therapy with vancomycin is indicated in patients at risk for MRSA septic arthritis 3.
Clinical Approach
- The diagnosis of septic arthritis is primarily based on history and clinical presentation of a red, warm, swollen, and painful joint with limited range of motion, supported by laboratory values and inflammatory markers from serum and joint fluid 1.
- Important risk factors for development of septic arthritis include age of >60 years, recent bacteremia, diabetes, cancer, cirrhosis, renal disease, drug or alcohol abuse, a history of corticosteroid injection, a recent injury or surgical procedure, a prosthetic joint, and a history of rheumatoid arthritis 1.