In adult patients with diabetes or peripheral arterial disease, how does the prognosis, functional outcome, and mortality of bilateral below‑knee amputation (BKA) compare to above‑knee amputation (AKA)?

BKA vs AKA Prognosis in Diabetic and PAD Patients

Below-knee amputation (BKA) offers superior functional outcomes and prosthetic rehabilitation compared to above-knee amputation (AKA), but this advantage is meaningful only when the knee joint can be preserved with successful wound healing—mortality rates are similarly high for both levels, and the majority of elderly vascular patients will not achieve outdoor ambulation regardless of amputation level. 1, 2

Mortality Outcomes

Mortality is comparable between BKA and AKA, with no significant survival advantage for either level:

• 30-day operative mortality ranges from 8.5-10% for both BKA and AKA in contemporary series 2, 3
• One-year mortality is approximately 22% for both levels 2, 4
• Three-year survival is only 55% across all major amputations, reflecting the severe burden of cardiovascular disease in this population 2
• Five-year mortality in diabetic patients with PAD approaches 50%, comparable to aggressive malignancies 1, 5

The decision between BKA and AKA should not be based on mortality considerations, as survival is driven by underlying cardiovascular disease rather than amputation level. 1, 2

Wound Healing and Revision Surgery

BKA carries substantially higher rates of wound complications and conversion to AKA:

• BKA healing at 100 days is only 55% compared to 76% for AKA 2
• By 200 days, healing rates converge (83% BKA vs 85% AKA), but this reflects conversion of failed BKAs to AKA 2
• 35% of BKAs require additional operative revision for wound management 3
• 16-25% of BKAs ultimately require conversion to AKA due to failed healing 2, 3
• AKA requires revision in only 13.5% of cases 3

This higher morbidity must be weighed against potential functional benefits—attempting BKA is justified only when objective vascular parameters predict healing success. 1

Functional Outcomes and Prosthetic Use

BKA provides superior prosthetic rehabilitation potential, but actual functional outcomes in elderly vascular patients are poor regardless of level:

Prosthetic Fitting Rates

• BKA: 85% prosthetic fitting rate 3
• AKA: 66% prosthetic fitting rate 3
• In contemporary series, only 32-42% of all major amputees actually use prosthetic limbs long-term 2

Ambulation Outcomes at 12-17 Months

• Outdoor ambulation: 21-29% of all major amputees 2
• Indoor-only ambulation: 25-28% 2
• Non-ambulatory: 46-51% despite prosthetic fitting 2

Level-Specific Ambulation

• BKA: 84% of prosthetic users achieve walking with artificial limb 3
• AKA: Only 22% of prosthetic users achieve walking with artificial limb 3
• However, one modern UK series found no significant difference in independent mobility between BKA (54.5%) and AKA (45.1%) at one year, suggesting the theoretical advantage of knee preservation may not translate to real-world function in elderly vascular patients 4

Bilateral Amputation Considerations

Bilateral BKA offers the only realistic chance for prosthetic ambulation in bilateral amputees, but success rates are low:

• Among elderly bilateral amputees, 50% of bilateral BKA patients achieved prosthetic use with both limbs 6
• No patients with bilateral AKA or BKA-AKA combinations were successfully fitted with two prostheses 6
• Successful bilateral prosthetic use requires: age <70 years, successful prosthetic use after first amputation, and absence of severe cardiac or pulmonary comorbidities 6

For bilateral amputation, every effort must be made to preserve at least one knee joint—bilateral AKA essentially eliminates any possibility of prosthetic ambulation. 6

Decision Algorithm for Amputation Level

Attempt BKA When:

• Ankle pressure ≥50 mmHg or ABI ≥0.5 1
• Toe pressure ≥30 mmHg 1
• TcPO₂ ≥25-30 mmHg 1, 7
• Skin perfusion pressure ≥40 mmHg 1, 7
• Patient age <70 years with reasonable functional status 6, 4
• Absence of extensive tissue necrosis extending above the malleolus 1

Proceed Directly to AKA When:

• Life-threatening sepsis requiring emergency amputation for source control 1
• Extensive tissue necrosis rendering the foot functionally unsalvageable even with revascularization 1
• Ankle pressure <50 mmHg AND failed or impossible revascularization 1
• Severe flexion contracture of the knee preventing prosthetic fitting 1
• Patient is non-ambulatory at baseline and has no rehabilitation potential 2, 4

Consider Through-Knee Amputation When:

• BKA is not feasible due to inadequate perfusion or tissue loss 8, 3
• Patient has rehabilitation potential but cannot tolerate the higher morbidity of attempted BKA 3
• Through-knee amputation offers operative mortality (8.5%) and prosthetic gait (66%) nearly equivalent to BKA, with lower re-amputation rates than BKA (25% vs 16%) 3
• Note: No RCTs exist comparing through-knee to AKA, but observational data suggest functional superiority over AKA 8, 3

Quality of Life Considerations

Major factors influencing post-amputation quality of life:

• Walking with a prosthesis is the single most important determinant of quality of life 1
• AKA (versus BKA) is associated with significantly lower quality of life 1
• Age >65 years, diabetes, and social isolation (homebound status) all reduce quality of life 1
• 17% of patients who lived independently before amputation require nursing facility placement after major amputation 2

Critical Pitfalls to Avoid

• Do not attempt BKA based solely on palpable pulses—objective vascular assessment with ABI, toe pressures, or TcPO₂ is mandatory 1, 5, 7
• Do not pursue aggressive BKA attempts in patients with ankle pressure <50 mmHg without successful revascularization—the 35% revision rate and 16-25% conversion rate to AKA subjects patients to multiple operations with poor ultimate function 2, 3
• Do not assume BKA will result in outdoor ambulation in elderly vascular patients—only 21-29% achieve this level of function, and 46-51% remain non-ambulatory despite prosthetic fitting 2
• Do not delay primary AKA in non-ambulatory patients with poor functional status—the morbidity of failed BKA attempts (multiple revisions, prolonged wound care, delayed rehabilitation) outweighs theoretical functional benefits that will never be realized 2, 4
• Do not make amputation decisions based on perfusion measures alone—multidisciplinary team evaluation incorporating functional status, comorbidities, and rehabilitation potential is essential 1, 5