How should a postoperative knee infection with redness and serous drainage be managed?

Management of Postoperative Knee Infection with Redness and Serous Drainage

The primary and most critical treatment is immediate opening of the surgical incision with evacuation of infected material, followed by dressing changes until healing by secondary intention; antibiotics should only be added if systemic signs of infection are present (temperature >38.5°C, heart rate >110 bpm, erythema extending >5 cm from wound edge, or signs of systemic inflammatory response). 1, 2, 3

Immediate Assessment and Surgical Management

Open the incision immediately and perform incision and drainage as the cornerstone of treatment. 1, 2, 3 This is non-negotiable for all surgical site infections regardless of severity. The physical appearance of the incision provides the most reliable diagnostic information, with local signs of pain, swelling, erythema, and drainage typically present. 1

Key Steps for Surgical Intervention:

• Remove any sutures present at the infected site 1, 2
• Evacuate all purulent or serous material completely 1, 3
• Perform wound irrigation and debridement as needed 1
• Continue wet-to-dry dressing changes until the wound heals by secondary intention 1, 3
• Obtain Gram stain and culture of wound drainage before starting antibiotics 1, 2

Decision Algorithm for Antibiotic Use

Most superficial surgical site infections do NOT require antibiotics after adequate drainage. 1, 2, 3 The critical error is reflexively prescribing antibiotics when drainage alone is sufficient.

Add Systemic Antibiotics ONLY if ANY of the following are present:

• Temperature >38.5°C 1, 3
• Heart rate >110 beats/minute 1, 3
• Erythema and induration extending >5 cm from the wound edge 1, 3
• White blood cell count >12,000/μL 3
• Patient is immunocompromised 1, 3
• Signs of systemic inflammatory response syndrome (SIRS) or organ dysfunction 1, 3

If none of these criteria are met, proceed with drainage alone and close observation. 1, 2, 3

Empiric Antibiotic Selection (When Indicated)

For postoperative knee infections requiring antibiotics, the choice depends on the surgical procedure type and local resistance patterns:

For Clean Orthopedic Procedures (Knee Arthroplasty):

• First-line: Cefazolin 1-2g IV every 8 hours 1, 2, 4
• Alternative: Nafcillin or oxacillin 2g IV every 6 hours 2, 3
• Oral step-down: Cephalexin 500mg every 6 hours 3

If MRSA is Suspected or Confirmed:

• Vancomycin 15 mg/kg IV every 12 hours 1, 2, 3
• Alternatives: Linezolid, daptomycin, or ceftaroline 2

MRSA Risk Factors to Consider:

• Recent hospitalization within 30 days 1
• Long-term care facility residence 1
• Prior antibiotic exposure (especially cephalosporins, carbapenems, or quinolones) 1
• Age ≥75 years 1
• Current hospitalization >16 days 1
• Prosthesis implantation 1

Duration of Antibiotic Therapy

If antibiotics are indicated, treat for 5-7 days after adequate drainage. 2, 3 A common pitfall is continuing antibiotics beyond this timeframe without clear indication. 2

• For minimal systemic signs: 24-48 hours may be sufficient 1, 3
• For significant systemic involvement: 5-7 days is typically adequate 2, 3
• Longer courses are rarely needed unless there is deep tissue involvement or the patient is severely immunocompromised 2

Critical Pitfalls to Avoid

Do not rely on antibiotics alone without surgical drainage when an infection is present. 1, 2, 3 This is the most common error and leads to treatment failure. Studies consistently show that antibiotics without drainage have minimal benefit for surgical site infections. 1

Do not assume all postoperative redness requires antibiotics. 1 Flat, erythematous changes around a surgical incision during the first week without swelling or drainage often resolve without any treatment, including antibiotics. 1

Investigate for deeper infection if the wound does not respond as expected. 1, 3 Any deep surgical site infection that fails to improve after appropriate treatment should raise suspicion for a deeper organ/space infection. 1

Ensure tetanus prophylaxis is current (within 10 years), preferably with Tdap if not previously given. 1

Monitoring and Follow-up

• Reassess within 24-48 hours after drainage to ensure clinical improvement 3
• If fever persists beyond 36 hours despite adequate drainage and antibiotics, consider imaging (MRI or CT) to evaluate for deeper infection 1
• Blood cultures should be obtained if systemic toxicity is present 1
• Adjust antibiotics based on culture results once available 1, 2