What are the primary indications for Below-Knee Amputation (BKA)?

Primary Indications for Below-Knee Amputation (BKA)

Below-knee amputation is primarily indicated when chronic limb-threatening ischemia (CLTI) cannot be successfully revascularized, when extensive necrosis or infectious gangrene threatens life, or when the patient is non-ambulatory with severe comorbidities making revascularization futile. 1

Life-Threatening Emergency Indications

Primary amputation is immediately indicated when life takes priority over limb, specifically in these clinical scenarios:

• Advanced soft-tissue infection requiring emergency sepsis control where amputation is the only option to prevent death 1
• Severe metabolic derangements from extensive tissue necrosis 1
• Infectious gangrene with systemic sepsis 1

Chronic Limb-Threatening Ischemia (CLTI) Indications

BKA should be considered in CLTI patients presenting with:

• Ischemic rest pain with objective hemodynamic confirmation (ABI <0.40, ankle pressure <50 mmHg, toe pressure <30 mmHg, TcPO2 <30 mmHg) 1
• Non-healing ulceration ≥2 weeks duration 1
• Gangrene involving any portion of the foot or lower limb 1
• Diabetic foot ulcer with critical ischemia 1

When Revascularization Has Failed or Is Not Feasible

Primary amputation becomes appropriate after thorough evaluation by an experienced revascularization specialist in these specific situations: 1

• Failed revascularization attempts with continued limb deterioration from infection or necrosis despite patent grafts 1
• No-option patients where anatomically there is no suitable target vessel for bypass or endovascular intervention 1
• Extensive tissue destruction where surgical resection would result in a non-functional extremity 1

Patient-Specific Indications

Functional Status Considerations

BKA is preferred over above-knee amputation when feasible because it preserves the knee joint, improving rehabilitation potential and prosthetic function. 1 However, primary above-knee amputation may be more appropriate for:

• Non-ambulatory or entirely bedbound patients at baseline due to chronic comorbidity (stroke, persistent vegetative state) 1
• Patients with end-stage renal failure (ESRF) who have higher risk of BKA failure requiring conversion to above-knee amputation 2
• Preoperative non-ambulatory status, which independently predicts subsequent conversion to above-knee amputation (OR=5.58) 2

Comorbidity Considerations

The European Society of Cardiology guidelines note that patients who are moribund may be best served with adequate analgesia and supportive measures rather than amputation. 1 When amputation is necessary, consider patient factors:

• Short life expectancy (advanced age, untreatable cancer) 1
• Severe dementia (HR 2.769 for mortality) 3
• Heart failure (HR 2.013 for mortality) 3
• Renal failure (HR 1.87 for mortality; OR 3.85 for conversion to above-knee amputation) 3, 2

Special Circumstance: Wet Gangrene

For patients with wet gangrene, a two-stage procedure is superior to one-stage BKA, with significantly better primary stump healing (Peto OR 0.08,95% CI 0.01 to 0.89). 4 This involves:

1. Initial guillotine amputation at the ankle for infection control 4, 5
2. Definitive long posterior flap BKA after infection resolution 4

Critical Pitfalls to Avoid

Do not perform BKA based solely on clinical assessment of tissue viability—objective hemodynamic measurements are essential. 6 Key considerations:

• Skin perfusion pressure (SPP) below 30 mmHg predicts high failure rates: 54% failure with SPP 20-30 mmHg, 89% failure with SPP <20 mmHg 6
• Clinical signs of ischemia are unreliable: only 1 of 15 failed BKAs at low pressures had warning signs of local ischemia 6
• Popliteal artery pulsations indicate 89% chance of BKA healing 6
• Resistant bacterial infection increases reoperation risk (HR 3.083) 3

Post-Amputation Considerations

All BKA patients require indefinite antiplatelet therapy unless contraindicated. 1 The 2024 ACC/AHA guidelines emphasize that customized longitudinal care is essential after minor amputation, including: 1

• Local wound care and pressure offloading 1
• Therapeutic footwear for high-risk patients 1
• Evaluation at least twice annually by a vascular specialist 1
• Management of diabetes and cardiovascular comorbidities 1

Wound complications and hospital readmission rates are high (20% wound infection rate), reflecting the burden of advanced cardiovascular disease, diabetes, and ongoing smoking in this population. 1, 2