What is the best course of action for a post-operative knee arthroscopic surgery patient presenting with fever and leukocytosis (elevated white blood cell count)?

Post-Operative Knee Arthroscopy with Fever and Leukocytosis

Immediately obtain ESR, CRP, and proceed directly to knee joint aspiration for synovial fluid analysis with cell count, differential, and culture to rule out septic arthritis, as this represents a surgical emergency requiring urgent intervention. 1, 2, 3

Immediate Diagnostic Workup

Laboratory Testing (Obtain Stat)

• Draw ESR and CRP immediately - these are the most useful screening tools, with CRP showing 73-91% sensitivity and 81-86% specificity for prosthetic knee infection at a cutoff of ≥13.5 mg/L 1, 2, 3
• Add interleukin-6 testing - this provides higher predictive value than traditional markers and shows excellent sensitivity when combined with CRP 1, 2, 4
• Do NOT rely on peripheral WBC count - leukocyte counts are NOT elevated in most patients with infected prostheses, making your elevated white count concerning but not diagnostic 1, 2, 3
• Obtain blood cultures if systemically ill - particularly if fever is high-grade or patient appears septic 4

Joint Aspiration (Perform Urgently)

• Proceed immediately to knee aspiration if ESR/CRP are elevated or clinical suspicion is high 2, 3
• Synovial fluid WBC count >3,000 cells/µL is the most precise test with 100% sensitivity, 98% specificity, and 99% accuracy for infection 5
• Send synovial fluid for cell count, differential, Gram stain, and culture 1, 2, 4
• Withhold antibiotics for at least 2 weeks prior to aspiration if clinically feasible to avoid false-negative cultures 2, 3
• Consider synovial fluid alpha-defensin testing - this has 97% sensitivity and 96% specificity, increasing to 100% specificity when combined with synovial CRP 4

Imaging

• Obtain plain radiographs of the knee first - look for signs of loosening, osteolysis, or component migration that may accompany infection 1, 2, 3
• Advanced imaging is NOT indicated initially - nuclear medicine studies (labeled WBC scans, bone scans) have limited utility with sensitivities of only 40-96% and are expensive and complex 1

Clinical Assessment Priorities

Key Historical and Physical Findings

• Assess pain pattern specifically - night pain or pain at rest is characteristic of infection, whereas pain on weight-bearing suggests mechanical loosening 1, 2, 3
• Do NOT exclude infection based on absence of classic signs - chronic infections frequently present with pain alone without fever, erythema, or warmth 2, 3
• Examine the wound carefully - look for purulent drainage, erythema extending >5 cm from incision, warmth, or swelling 1
• Document systemic symptoms - temperature trends, heart rate, and overall clinical appearance 1

Timing Considerations

• Fever within first 48 hours post-op is usually benign and rarely represents surgical site infection unless due to Streptococcus pyogenes or Clostridium species 1, 6
• After 48 hours, surgical site infection becomes more likely and warrants direct wound inspection 1, 6
• Fever at 2-4 weeks post-operatively with elevated CRP demands aggressive workup - this pattern is associated with early acute periprosthetic infection 7

Antibiotic Decision Algorithm

When to START Antibiotics

• Hold antibiotics initially until after joint aspiration is performed (if patient is stable) to maximize culture yield 2, 3
• Start empiric antibiotics immediately if:
  • Temperature >38.5°C with heart rate >110 bpm 1
  • Erythema extending >5 cm beyond wound margins 1
  • Patient appears septic or hemodynamically unstable 1
  • Gram stain shows organisms 1

Empiric Coverage

• Target Staphylococcus aureus and coagulase-negative Staphylococcus (including S. epidermidis) - these are the most common organisms in periprosthetic infections 1
• Consider MRSA coverage based on local resistance patterns and patient risk factors 1

Critical Pitfalls to Avoid

• Do NOT dismiss normal peripheral WBC as reassuring - most infected prostheses do NOT cause leukocytosis 1, 2, 3
• Do NOT wait for "classic" infection signs - pain alone may be the only manifestation of chronic infection 2, 3
• Do NOT obtain urine cultures reflexively - fever and leukocytosis in post-operative patients are NOT associated with UTI in the early post-operative period 8
• Do NOT attribute early fever to atelectasis - this is a myth; focus on surgical site, pulmonary embolism, pneumonia, or drug fever instead 6
• Do NOT start antibiotics before aspiration unless patient is unstable - this dramatically reduces culture sensitivity 2, 3

Expected Cytokine Response vs. Infection

• Normal post-operative IL-6 elevation peaks at 24 hours and correlates with surgical trauma, not necessarily infection 9
• Persistently elevated or rising inflammatory markers at 2-4 weeks suggest infection rather than normal surgical response 7
• CRP normally returns to baseline within 2 months after uncomplicated surgery 1

Most Likely Organisms

• Staphylococcus aureus (most common) 1
• Coagulase-negative Staphylococcus (including S. epidermidis) 1
• Streptococcus pyogenes or Clostridium species if presenting within 48 hours with dramatic findings 1