What are the immediate management steps for a post-operative septic knee patient, including necessary labs and clinical signs to monitor?

Management of Post-Operative Septic Knee

Immediate surgical source control through arthroscopic irrigation and debridement combined with prompt intravenous antibiotics within one hour is the definitive treatment for post-operative septic knee. 1, 2, 3

Immediate Actions (Within First Hour)

Clinical Assessment - Key Signs to Monitor

• Pain characteristics: Night pain or pain at rest is characteristic of infection, whereas pain on weight bearing suggests mechanical loosening 1
• Acute infection signs: Pain, swelling, warmth, erythema, and fever are common in acute presentations 1
• Chronic infection: May present with pain alone without other inflammatory signs 1
• Systemic signs: Fever is present in approximately 85% of cases 3
• Joint examination: Limited range of motion, effusion, and warmth 4

Laboratory Workup - Essential Tests

Order these labs immediately:

• ESR and CRP: These are more sensitive than radiographs for detecting infection and should be obtained first 5, 2

  • CRP sensitivity: 73-91%, specificity: 81-86% (cutoff ≥13.5 mg/L) 1
  • When both ESR and CRP are negative, infection is unlikely 1, 5
  • Positive results for either warrant further evaluation 1, 5

• Serum lactate: Measure as a marker of tissue hypoperfusion in septic patients 2

• Blood cultures: Obtain at least two sets before starting antimicrobials, but do not delay treatment beyond 45 minutes 2

• Joint aspiration: Extremely useful and should be performed if laboratory markers are elevated or clinical suspicion remains high 5

  • Synovial fluid leukocyte count >25,000/μL suggests infection 3
  • Send for culture and sensitivity 3, 4
  • Image-guided aspiration recommended for accurate needle placement 5

Imaging

• Plain radiographs: Obtain as initial study to provide anatomic overview and exclude other pathologies, though they have significant limitations for diagnosing infection 5
• Look for indirect signs: joint effusion, soft tissue swelling, periosteal reaction 5

Definitive Treatment Protocol

Surgical Management - First Priority

Perform arthroscopic irrigation and debridement immediately: 1, 2, 3

• Timing is critical: Source control interventions should be implemented as soon as possible after diagnosis 2
• Technique: Arthroscopic debridement with thorough irrigation and synovectomy 3, 6
• Graft retention: In post-ACL reconstruction cases, the graft can often be retained with early intervention 7, 6
• Hardware considerations: Remove any foreign body or device that may be the source of infection 1
• Repeat procedures: If clinical improvement is not seen within 48-72 hours, repeat irrigation may be necessary 1, 6

Antibiotic Therapy - Start Within One Hour

Empiric broad-spectrum coverage: 2, 3, 4

• Initial regimen: Anti-MRSA agent (vancomycin) plus cephalosporin to cover Staphylococcus species (most common pathogen) and gram-negative organisms 3, 4

• Route: Intravenous antibiotics are superior to oral for initial treatment 3

• Duration:

  • IV antibiotics until fever resolves and CRP normalizes (typically 4 weeks) 3
  • Followed by oral antibiotics for additional 12 weeks 8
  • Total duration typically 7-10 days for uncomplicated cases, longer for slow clinical response 2

• De-escalation: Reassess antimicrobial regimen daily once culture results available and narrow spectrum accordingly 1, 2

Hemodynamic Support (If Septic Shock Present)

Resuscitation targets: 2

• Fluid resuscitation: 30 mL/kg crystalloid for hypotension or lactate ≥4 mmol/L 2
• Vasopressor: Norepinephrine as first-choice to maintain MAP ≥65 mmHg 2
• Corticosteroids: Consider hydrocortisone (up to 300 mg/day) in patients requiring escalating vasopressor doses 1, 2
• Monitoring: Measure arterial blood pressure and heart rate frequently 1

Post-Treatment Monitoring

Clinical Response Indicators

• Resolution timeline: Local signs should resolve within 4 weeks with appropriate treatment 3
• Fever: Should disappear within 4 weeks with IV antibiotics 3
• CRP normalization: Should occur within 4 weeks 3
• Failure indicators: Worsening or ongoing symptoms for >48-72 hours questions adequacy of treatment 1

Follow-up Assessment

• Range of motion: Should return to full symmetric motion 7
• Effusion: Should resolve completely 7
• Functional scores: Lysholm scores typically >90 with successful treatment 7, 6

Critical Pitfalls to Avoid

• Delayed antibiotic administration: Each hour of delay increases mortality by 7.6% 2
• Relying solely on radiographs: They are neither sensitive nor specific and often normal in early infection 5
• Inadequate source control: Failure to perform surgical debridement promptly leads to persistent sepsis 2
• Premature discontinuation of antibiotics: Ensure complete treatment course to prevent recurrence 3, 8
• Missing repeat debridement need: If no improvement in 48-72 hours, repeat surgical intervention is required 1, 6