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

Primary Indications for Below-Knee Amputation (BKA)

Below-knee amputation is primarily indicated for life-threatening infectious gangrene with systemic sepsis, extensive tissue necrosis causing severe metabolic derangements, chronic limb-threatening ischemia (CLTI) with non-healing ulceration or gangrene, and in patients where revascularization has failed or is not feasible. 1

Life-Threatening Emergency Indications

These represent absolute indications where amputation must be performed urgently to save the patient's life:

• Infectious gangrene with systemic sepsis requires immediate primary amputation as the only option to prevent death 2, 1
• Advanced soft-tissue infection requiring emergency sepsis control where amputation is necessary to control overwhelming infection 1
• Severe metabolic derangements from extensive tissue necrosis that threaten systemic stability 1

In these emergency scenarios, life takes absolute priority over limb salvage, and delay for attempted revascularization is contraindicated 1.

Chronic Limb-Threatening Ischemia (CLTI) Indications

BKA should be considered in CLTI patients presenting with the following clinical scenarios:

• Ischemic rest pain with objective hemodynamic confirmation (ankle-brachial index <0.4 or toe pressure <30 mmHg) 1
• Non-healing ulceration ≥2 weeks duration despite optimal wound care and revascularization attempts 1
• Gangrene involving any portion of the foot or lower limb where tissue viability cannot be restored 1
• Diabetic foot ulcer with critical ischemia where revascularization has failed or is not possible 1

Important Caveat on Revascularization

Primary amputation in CLTI should only be performed after revascularization has been attempted or deemed not feasible 2. The European Society of Cardiology emphasizes that patients with extensive necrosis or infectious gangrene may best be served with primary amputation, but this decision should follow evaluation by a multispecialty care team except in life-threatening sepsis 2, 1.

Patient-Specific Factors Influencing Amputation Level

When BKA is Preferred

• BKA should be chosen over above-knee amputation whenever technically feasible because preserving the knee joint dramatically improves rehabilitation potential and prosthetic function 1
• Patients with adequate tissue perfusion at the below-knee level (as evidenced by transcutaneous oxygen pressure >30-40 mmHg or adequate skin bleeding) are candidates for BKA 1

When Above-Knee Amputation May Be More Appropriate

• Non-ambulatory or entirely bedbound patients at baseline due to chronic comorbidity may benefit from primary above-knee amputation, as the rehabilitation advantage of BKA is lost in this population 1, 3
• End-stage renal failure (ESRF) patients have significantly higher rates of BKA failure requiring conversion to above-knee amputation (odds ratio 3.85), and may benefit from direct above-knee amputation if major amputation is required 3
• Preoperative non-ambulatory status is an independent risk factor (odds ratio 5.58) for requiring subsequent above-knee amputation after initial BKA 3

Common Pitfalls and Clinical Pearls

Staged Amputation for Wet Gangrene

• In the presence of wet gangrene, a two-stage procedure is superior to one-stage definitive amputation 4
• The first stage involves guillotine amputation at the ankle or transtibial level to achieve rapid infection decompression and drainage 4, 5
• The second stage involves definitive long posterior flap BKA after infection control is achieved 4
• This approach leads to significantly better primary stump healing (Peto OR 0.08,95% CI 0.01 to 0.89) compared to one-stage procedures 4

Microvascular Disease Assessment

• Traditional markers of peripheral arterial disease (PAD) do not predict wound complications after BKA formalization 6
• The presence of small-vessel atherosclerosis or arteriosclerosis on pathology is the only significant predictor of wound complications (P = 0.03) 6
• Patients with diabetes and wet gangrene may have significant microvascular disease even without documented large-vessel PAD 6

Mortality and Comorbidity Considerations

• Both BKA and above-knee amputation are associated with very high mortality rates (25% at 1 year, 34% at 2 years) 7
• Risk factors for mortality include dementia (HR 2.769), non-ambulatory status preoperatively (HR 2.281), heart failure (HR 2.013), and renal failure (HR 1.87) 7
• Resistant bacterial infection is associated with high rates of reoperation (HR 3.083) 7

Post-Amputation Management Requirements

All BKA patients require comprehensive longitudinal care:

• Indefinite antiplatelet therapy unless contraindicated 1
• Evaluation at least twice annually by a vascular specialist due to high incidence of recurrence 1
• Local wound care and pressure offloading during healing 1
• Therapeutic footwear for high-risk patients after healing 1
• Management of diabetes and cardiovascular comorbidities 1