In suspected septic arthritis of the knee, what is the immediate step?

• A. MRI of the knee
• B. Emergent joint aspiration with Gram stain/culture and start IV antibiotics
• C. Observation with rest
• D. Oral antibiotics

Answer: (B)

Septic arthritis is a surgical emergency, so the immediate move is to obtain joint fluid and start treatment right away. Emergent aspiration of the knee joint to obtain synovial fluid for Gram stain and culture serves both diagnostic and therapeutic purposes: it confirms infection, guides antibiotic choices, and provides rapid relief of pressure and bacterial load. Along with obtaining the sample, start intravenous antibiotics promptly to cover the most common organisms (staphylococci, including MRSA, and common gram-negative bacteria) while cultures are pending. This approach minimizes joint cartilage damage and systemic complications.

Delaying for imaging like MRI can waste precious time and doesn’t replace the need for fluid analysis or early antibiotics. Observation and rest won’t address an infection in the joint, and oral antibiotics are not sufficient for an active septic process.