What is the recommended treatment for septic arthritis?

Septic Arthritis Diagnosis and Treatment

Immediate Diagnostic Approach

Joint aspiration with synovial fluid analysis is the definitive diagnostic procedure and must be performed immediately before antibiotics are administered to maximize identification of the causative organism. 1, 2, 3

Clinical Presentation

• Acute onset of monoarticular joint pain, erythema, heat, and immobility are the hallmark features 4
• Constitutional symptoms (fever, chills, rigors) are poorly sensitive and cannot rule out septic arthritis 4
• Septic arthritis is an orthopedic emergency requiring urgent treatment to prevent irreversible cartilage damage and joint destruction 1, 2

Synovial Fluid Analysis Thresholds

• White blood cell count ≥50,000 cells/mm³ is suggestive of septic arthritis in patients who have NOT received antibiotics 5, 1, 4
• If antibiotics were given within 2 weeks before arthrocentesis, lower the diagnostic threshold to >16,000 cells/mm³ (sensitivity 82%, specificity 76%) 6
• Neutrophil percentage >90% supports the diagnosis in antibiotic-exposed patients 6
• Synovial fluid culture is positive in approximately 80% of non-gonococcal cases and is essential for definitive diagnosis 5, 1

Critical Diagnostic Pitfall

• Negative joint aspirate culture does NOT rule out infection—if clinical suspicion remains high, consider percutaneous image-guided bone biopsy 5, 1, 2
• Always send synovial fluid for cell count with differential, Gram stain, culture, AND crystal analysis to exclude coexistent gout (which occurs in 4% of septic arthritis cases) 5, 3

Treatment Algorithm

Step 1: Determine Surgical Urgency

• Surgical emergencies (sepsis, immunocompromised status, extensive joint destruction) proceed directly to operating room for arthrotomy, irrigation, debridement, and intraoperative cultures 5, 1, 3
• Non-emergency cases undergo joint aspiration first 5, 3

Step 2: Drainage of Purulent Material

• All cases require evacuation of purulent material—either through repeated arthrocentesis, arthroscopic drainage, or open surgical debridement 1, 2, 4
• Arthroscopic irrigation and debridement is effective in 91% of cases when combined with antibiotics 7
• Ultrasound guidance improves aspiration success, especially for difficult-to-access joints like shoulder and hip 3, 8

Step 3: Empiric Antibiotic Therapy

Initiate IV vancomycin immediately after obtaining synovial fluid to cover MRSA, which is the most common pathogen (42% of cases). 1, 2, 4

Empiric Regimens Based on Gram Stain:

• Gram-positive cocci: Vancomycin 4
• Gram-negative cocci: Ceftriaxone 4
• Gram-negative rods: Ceftazidime 4
• Negative Gram stain with high clinical suspicion: Vancomycin PLUS ceftazidime or aminoglycoside 4

Adjunctive Therapy for MRSA:

• Consider adding rifampin 600 mg daily (or 300-450 mg twice daily) to vancomycin for MRSA due to excellent bone and biofilm penetration 1, 2

Step 4: Pathogen-Specific Considerations

Adjust empiric coverage based on patient risk factors:

• Sexually active young adults: Consider Neisseria gonorrhoeae 3, 9
• Children <4 years: Consider Kingella kingae 1, 2, 3
• Sickle cell disease: Consider Salmonella species 1, 2, 3
• Polymicrobial infection: Dual antibiotic coverage is mandatory (e.g., linezolid for MRSA plus ciprofloxacin for Pseudomonas) 1

Step 5: Duration of Antibiotic Therapy

• Uncomplicated septic arthritis: 3-4 weeks of antibiotics 1, 2
• Concomitant osteomyelitis (occurs in 30% of pediatric cases): Longer treatment required 1, 2, 3
• Prosthetic joint infections: 12 weeks shows better outcomes than 6 weeks 1, 2
• Oral antibiotics are not inferior to IV therapy in most cases and can be used after initial IV treatment 9

Step 6: Monitoring Treatment Response

• Follow C-reactive protein and erythrocyte sedimentation rate to monitor treatment response 3
• For persistent or recurrent joint swelling after oral antibiotics: Re-treat with another 4-week course of oral antibiotics OR 2-4 weeks of IV ceftriaxone 1, 2

Special Situations

Prosthetic Joint Infections

• Device removal is recommended 2
• If device cannot be removed, chronic suppression with appropriate antibiotics is necessary 2
• Lower diagnostic thresholds apply: synovial fluid WBC >1,100 cells/mm³ with neutrophils >64% suggests infection 4

Persistent Synovitis

• Arthroscopic synovectomy may reduce duration of joint inflammation in cases with significant pain or functional limitation 1, 2
• Consider symptomatic treatment with NSAIDs if arthritis persists despite IV therapy and synovial fluid PCR is negative 1

Common Pitfalls to Avoid

1. Do NOT wait for culture results to start antibiotics after obtaining synovial fluid 1, 2, 3
2. Do NOT use the 50,000 cells/mm³ cutoff if antibiotics were given before arthrocentesis—use 16,000 cells/mm³ instead 6
3. Do NOT assume negative cultures rule out infection, especially if antibiotics were given first 3
4. Do NOT forget to check for coexistent gout—sepsis and gout can occur in the same joint 5
5. Do NOT perform intra-articular corticosteroid injections during active infection 1