What is the treatment for a septic knee?

Treatment of Septic Knee

The treatment of septic knee requires immediate joint drainage combined with appropriate antibiotic therapy, with arthrocentesis being as effective as surgical approaches while resulting in shorter hospital stays and better functional outcomes. 1, 2

Diagnosis

Before initiating treatment, proper diagnosis is essential:

• Clinical presentation: Acute onset of joint pain, erythema, warmth, swelling, limited mobility, and pain at rest 1

• Laboratory tests:

  • Serum inflammatory markers: CRP >2.0 mg/dL, ESR ≥40 mm/hour 1
  • Joint aspiration (essential): Synovial fluid analysis showing:
    • WBC count >50,000 cells/mm³ with >90% neutrophils is highly suggestive 1
    • Neutrophil-to-lymphocyte ratio >25 (sensitivity 78%, specificity 81%) 1
    • Gram stain (positive in only about 50% of cases) 3
    • Culture for pathogen identification (S. aureus most common at 42%) 1, 4

• Imaging:

  • Plain radiographs to identify soft tissue swelling, joint effusion, and exclude fractures 5, 1
  • Ultrasound to detect joint effusions and guide aspiration 1
  • MRI with contrast if aspiration is inconclusive or to identify concurrent osteomyelitis 1

Treatment Algorithm

1. Joint Drainage

• Initial approach: Arthrocentesis (medical approach) or surgical drainage 2

  • Arthrocentesis: Effective first-line approach with shorter hospital stay (21 vs. 33 days) and fewer sequelae compared to surgery 2
  • Surgical options (if needed):
    • Arthroscopic irrigation and debridement (preferred in most cases) 6, 4
    • Open surgical drainage (for advanced cases) 4

• Number of procedures:

  • Most patients require only 1 procedure with arthroscopic approach 6
  • Early intervention is critical - delay increases need for multiple procedures 6
  • Frequency of repeated procedures depends on infection stage:
    • Stage I (early): 5% need repeat procedures
    • Stage II (moderate): 52% need repeat procedures
    • Stage III (advanced): 75% need repeat procedures 4

2. Antibiotic Therapy

• Initial empiric therapy: Start immediately after obtaining synovial fluid samples 1

  • Cover for MRSA with vancomycin, linezolid, daptomycin, or TMP-SMX 1
  • Adjust based on culture and sensitivity results 1
  • For MSSA: nafcillin, oxacillin, or cefazolin 1

• Duration:

  • Standard course: 3-4 weeks 1
  • Longer courses for concurrent osteomyelitis 1
  • Regular reassessment of effectiveness is essential 5

3. Supportive Care

• DVT prophylaxis: Use prophylactic heparin and/or elastic bandages 5
• Pain management: Opioids titrated cautiously in unstable patients 5
• Mobilization: Early mobilization once the patient is stable 5
• Monitoring: Follow inflammatory markers (ESR, CRP) to assess treatment response 1

Special Considerations

• Prosthetic joints: Lower threshold for diagnosis (WBC >1,100 cells/mm³ with >64% neutrophils), longer antibiotic courses, often require hardware removal 1
• Concurrent osteomyelitis: Common with septic arthritis, requires extended antibiotic therapy 1, 7
• Risk of complications: DVT and pulmonary emboli can occur as complications 7

Common Pitfalls to Avoid

• Delaying joint drainage
• Failing to obtain cultures before starting antibiotics
• Missing concurrent osteomyelitis
• Inadequate duration of antibiotics
• Premature discontinuation of antibiotics based on clinical improvement alone 1

The prognosis depends on early diagnosis and prompt treatment. Delayed treatment significantly increases the risk of joint destruction and need for multiple procedures 6, 4.