What is the treatment for an infected incision on the knee?

Treatment for Infected Incision on Knee

The primary treatment for an infected knee incision is prompt and wide opening of the surgical incision to evacuate infected material, with antibiotics added only if systemic signs of infection are present. 1

Initial Assessment and Management

Immediately open the incision widely to drain purulent material and infected tissue—this is more critical than antibiotic selection for most incisional surgical site infections (SSIs). 1 The wound should then heal by secondary intention with regular dressing changes. 1

When to Add Antibiotics

Antibiotics are NOT routinely required for most incisional SSIs after adequate drainage. 1 However, add antibiotics if any of the following are present:

• Temperature >38.5°C or heart rate >110 beats/minute 1, 2
• Erythema extending >5 cm from the wound edge 1, 2
• SIRS criteria or signs of organ failure 1
• Patient is immunocompromised 1
• WBC count >12,000 cells/μL 2

If these criteria are absent, manage with incision and drainage alone. 1, 3

Antibiotic Selection for Knee Incisions

For trunk or extremity operations away from axilla/perineum (which includes knee incisions), the recommended antibiotics are: 4, 1

First-Line Options:

• Oxacillin or nafcillin 2g every 6 hours IV 1
• Cefazolin 0.5-1g every 8 hours IV 4, 1, 5
• Cephalexin 500mg every 6 hours orally 4, 1
• Sulfamethoxazole-trimethoprim (oral option) 4

If MRSA is Suspected:

• Add vancomycin 15 mg/kg every 12 hours IV 1
• Alternative: clindamycin 4

Duration of Antibiotic Therapy

If antibiotics are indicated, a short course of 24-48 hours is usually sufficient after adequate drainage. 1, 2 Continue only until systemic signs resolve, not until the wound fully heals. 4

Wound Care After Opening

• Daily inspection is essential with dressing changes that promote a moist healing environment 2
• Sharp debridement of any devitalized tissue using scalpel or scissors 2
• No specific dressing type has proven superior—convenience and cost guide selection 2
• For heavily draining wounds, consider negative pressure-assisted wound closure (vacuum-assisted closure) 2

Critical Follow-Up

• First re-examination within 12-24 hours, then repeat evaluations until clear signs of healing 2
• Re-evaluate sooner if clinical signs worsen or WBC count increases 2
• Off-loading pressure from the knee is crucial for healing, especially if the incision is over weight-bearing areas 2

Common Pitfalls to Avoid

• Delayed drainage leads to progression of infection—do not wait to open the incision 1
• Inadequate drainage is more problematic than antibiotic choice—ensure complete evacuation of infected material 3
• Unnecessary antibiotics for simple SSIs that have been adequately drained 1, 3
• Failure to recognize deeper infection—if the wound doesn't resolve as expected, investigate for deeper organ/space infection 1

Special Consideration: Atypical Infections

If the infection fails to respond to standard treatment with negative initial cultures, consider nontuberculous mycobacterial (NTM) infection, particularly Mycobacterium fortuitum. 4 These infections present indolently and require:

• Multiple tissue samples sent for mycobacterial culture 4
• Prolonged culture-specific antibiotics 4
• Often require two-stage revision with complete excision of infected tissue if prosthetic material is present 4