What are the criteria and management for septic arthritis?

Septic Arthritis: Diagnostic Criteria and Management

Immediate Diagnostic Approach

Septic arthritis requires immediate joint aspiration for synovial fluid analysis combined with urgent surgical drainage and empiric antibiotics to prevent irreversible cartilage destruction within hours to days. 1

Clinical Diagnostic Criteria

The diagnosis is established through a combination of clinical signs and laboratory markers:

• Classic presentation includes acute monoarticular joint pain, swelling, and fever, though this complete triad occurs in only ~50% of cases 1
• Five key criteria that approach 100% likelihood when all are met: 1
  • Fever >101.3°F (38.5°C)
  • Erythrocyte sedimentation rate ≥40 mm/hour
  • White blood cell count ≥12,000 cells/mm³
  • Inability to bear weight
  • C-reactive protein >2.0 mg/dL

Definitive Diagnostic Procedure

• Joint aspiration is mandatory and represents the definitive diagnostic test 1
• Synovial fluid WBC ≥50,000 cells/mm³ is highly suggestive of septic arthritis 1
• Synovial fluid culture is positive in approximately 80% of non-gonococcal cases 1
• Critical caveat: Negative synovial fluid culture does not exclude infection—if clinical suspicion remains high, proceed with treatment and consider percutaneous bone biopsy 1

Imaging Algorithm

Start with ultrasound for hip joints, then proceed based on findings: 1

1. Ultrasound first to detect joint effusion and guide aspiration—absence of effusion virtually excludes septic arthritis (5% false negative rate in patients with symptoms <1 day) 2
2. Plain radiographs to exclude other conditions (fractures, tumors) 1
3. MRI with contrast when clinical suspicion remains high despite negative aspiration, or when symptoms persist/worsen despite treatment 1
4. MRI distinguishes septic arthritis from transient synovitis: decreased femoral head enhancement on early post-contrast imaging is seen only in septic arthritis 2, 3

Pathogen Considerations

Staphylococcus aureus is the most common pathogen at all ages and should guide empiric therapy: 1, 4

• Neonates: Group B streptococcus predominates 1
• Children <4 years: Kingella kingae is common 1
• Sickle cell disease: Consider Salmonella species 3
• All ages: S. aureus remains most common overall 1, 4

Immediate Management Protocol

Surgical Drainage

Surgical drainage is indicated in ALL cases of septic arthritis and must be performed immediately: 2, 1

• Hip and shoulder joints require open surgical drainage due to difficulty accessing these joints 5
• Arthroscopic or surgical drainage is mandatory when: 5
  • Symptoms persist >7 days
  • Patient has severe sepsis
  • Hip or shoulder involvement
• Repeated needle aspiration alone fails in 46% of cases (11 of 24 patients required subsequent surgical drainage) 5
• For prosthetic joint infections, device removal is required 2

Empiric Antibiotic Therapy

Start empiric antibiotics immediately after obtaining cultures—do not delay for culture results: 1

Adults

• IV vancomycin 15 mg/kg every 6 hours as first-line for MRSA coverage 1
• Alternatives: linezolid, daptomycin, or teicoplanin 1

Pediatrics

• IV vancomycin 15 mg/kg/dose every 6 hours 1
• Clindamycin 10-13 mg/kg/dose IV every 6-8 hours if local clindamycin resistance is low 1

Transition to Oral Therapy

Oral antibiotics are not inferior to IV therapy and should be initiated after 2-4 days if: 1

• Patient is clinically improving
• Afebrile
• Tolerating oral intake

Treatment Duration

Total antibiotic duration varies by clinical scenario: 1

• Uncomplicated bacterial arthritis: 3-4 weeks total (recent evidence suggests 2 weeks may be adequate after surgical drainage in select cases) 1
• Concomitant osteomyelitis: Longer treatment required 1
• Prosthetic joint with debridement and retention: Extended therapy 1
• Hip or knee prosthesis with exchange: Prolonged course 1

Critical Monitoring and Pitfalls

Assess for Concurrent Osteomyelitis

Over 50% of pediatric patients with septic arthritis have infection beyond the joint space on MRI: 2

• In metaphyseal osteomyelitis, >50% have joint effusions, with 75% confirmed as septic arthritis 2
• 40% of patients not responding to antibiotics have concurrent osteomyelitis 2
• Repeat MRI for worsening or persistent symptoms—results in management changes in 21% of cases 1

Treatment Response Monitoring

Monitor the following parameters: 1

• CRP and ESR to assess treatment response
• Vancomycin trough levels to adjust dosing and prevent toxicity
• Clinical improvement within 48-72 hours—if absent, reassess for concurrent osteomyelitis 3

Common Pitfalls to Avoid

• Never delay treatment waiting for imaging or culture results if clinical suspicion is high 3
• Do not assume single joint involvement—consider large field-of-view imaging when feasible 3
• Always reassess for concurrent osteomyelitis if patient fails to improve after 48-72 hours of appropriate antibiotics and drainage 3
• Negative culture does not exclude infection—treat based on clinical suspicion 1

Special Considerations for Prosthetic Joints

Prosthetic joint septic arthritis requires device removal: 2

• Two-stage exchange with resection arthroplasty separated by 3-6 months 2
• Antifungal therapy for at least 12 weeks after resection and at least 6 weeks after reimplantation (for fungal infections) 2
• If device cannot be removed: chronic suppression with fluconazole 400 mg daily (for susceptible Candida isolates) 2