What are the complication rates after a below knee amputation for necrotizing soft tissue infection?

Complication Rates After Below Knee Amputation for Necrotizing Soft Tissue Infection

Below knee amputation for necrotizing soft tissue infection carries a high complication rate of approximately 34.4%, with a 30-day mortality rate of 7.0% according to large database studies. 1

Major Complications

Mortality Risk Factors

Mortality after below knee amputation for necrotizing soft tissue infections is significantly influenced by several pre-existing conditions:

• Age-related risk: Patients aged 80 years or older have 3.36 times higher odds of mortality 2
• Pre-operative septic shock: Increases mortality risk by 6.36 times 2
• Renal insufficiency:
  • Pre-operative dialysis dependence increases mortality risk by 2.99 times 2
  • Renal disease is an independent predictor of mortality 1
• Coagulopathy: INR >1.5 increases mortality risk by 2.25 times 2
• Hepatobiliary disease: Bilirubin >1.0 mg/dL increases mortality risk by 2.05 times 2
• Other significant predictors:
  • Cardiac issues 1
  • History of sepsis 1
  • Steroid use 1
  • COPD 1

Surgical Site Complications

The most common major complications within 30 days of below knee amputation include:

• Return to operating room: 15.6% 1
• Wound infection: 9.3% 1
• Postoperative sepsis: 9.3% 1

Limb-Related Outcomes

For patients with necrotizing fasciitis of the lower extremity:

• Repeat debridements: Mean of 2 additional procedures (range 1-4) are often required 3
• Further amputation: Up to 41% of patients may require more proximal amputation 3

Factors Affecting Discharge Disposition

Patients are more likely to require discharge to inpatient rehabilitation or skilled nursing facilities if they have:

• Age ≥80 years: 2.49 times higher odds 2
• ASA class ≥3: 2.05 times higher odds 2
• Amputation vs. debridement only: 2.53 times higher odds 2

Long-Term Outcomes

• Infection control: Long-term control of infection is achieved in over 80% of cases when managed by experienced surgeons 4
• Recurrence risk: Foot infection recurs in 20-30% of diabetic patients, especially those with underlying osteomyelitis 4

Predictors of Complications

Independent predictors of postoperative complications include:

• History of sepsis 1
• Alcohol use 1
• Steroid use 1
• Cardiac issues 1
• Renal insufficiency 1
• Contaminated/infected wounds 1
• Diabetes mellitus: Significantly increases risk of amputation (p=0.017) 5
• Peripheral vascular disease: Increases amputation risk (p=0.033) 5
• Elevated LRINEC score: Associated with higher amputation rates (p=0.033) 5

Clinical Implications

1. Early intervention is critical: Delayed definitive debridement remains the single most important risk factor for death in necrotizing soft tissue infections 6

2. Multidisciplinary approach: A dedicated limb salvage team may improve outcomes for patients with necrotizing infections of the lower extremity 5

3. Risk stratification: Patients without any major risk factors (septic shock, dialysis dependence, coagulopathy, hepatobiliary disease, advanced age) have a significantly lower mortality rate of 7.3% 2

4. Surgical timing: Delay in surgical debridement beyond 12 hours from admission is associated with significantly higher mortality, higher incidence of septic shock, renal failure, and need for more surgical debridements 4

5. Surgical approach: The World Society of Emergency Surgery recommends removing only devitalized/infarcted skin while sparing normally perfused skin, with reassessment at second operation for questionable areas 4

By understanding these complication rates and risk factors, clinicians can better counsel patients and families about expected outcomes and implement appropriate preventive measures to reduce morbidity and mortality following below knee amputation for necrotizing soft tissue infection.