What are the considerations for deciding between below knee amputation (BKA) and above knee amputation (AKA) in patients with severe lower limb damage or disease?

Below-Knee vs Above-Knee Amputation: Decision Framework

When amputation is necessary, below-knee amputation (BKA) should be prioritized whenever feasible, as it provides superior functional outcomes, better quality of life, and higher rates of prosthetic use and independent ambulation compared to above-knee amputation (AKA). 1

Primary Decision Principle

The fundamental goal is to perform amputation at the most distal level that facilitates healing while providing maximal functional ability. 1 This requires evaluation by a multispecialty care team to assess wound healing potential and functional capacity. 1

Key Functional Differences

BKA Advantages:

• Preservation of the knee joint is critical - patients with BKA have significantly better physical quality of life scores and functional outcomes than those with AKA 2
• Higher prosthetic utilization - BKA patients wear their prosthesis more consistently and achieve better mobility 2
• Superior ambulation capacity - significantly greater proportion of BKA patients can walk 500 meters compared to AKA patients 2
• Better rehabilitation potential - the knee joint allows superior functional recovery and places less physiological strain on patients 2, 3

Quality of Life Impact:

The 2024 ACC/AHA guidelines explicitly identify above-knee amputation as a factor associated with LOWER quality of life, while walking with a prosthesis is associated with HIGHER quality of life. 1 This creates a compelling argument for BKA when possible, as BKA patients are more likely to successfully use prosthetics. 2

Clinical Decision Algorithm

1. Life vs Limb Assessment

Primary amputation at any level is indicated when: 1

• Life-threatening sepsis from foot infection requiring immediate source control
• Severe metabolic derangement from extensive tissue necrosis
• Hemodynamic instability with the limb as the source (ischemia, advanced infection)

2. Wound Healing Potential Assessment

For BKA to succeed, evaluate: 1

• Degree of ischemia (consider toe pressure, TcPO2 measurements)
• Extent of infection and tissue loss
• Presence of adequate tissue for coverage
• Vascular status and potential for healing

If infragenicular amputation healing is uncertain but patient is ambulatory, BKA should still be attempted - the functional benefits justify the attempt, with conversion to AKA as a secondary option if healing fails. 1

3. Patient Functional Status

Consider BKA strongly preferred for: 1

• Ambulatory patients at baseline
• Patients with rehabilitation potential
• Younger patients (age <65 associated with better outcomes) 1

Consider AKA acceptable for: 1

• Bedridden or non-ambulatory patients at baseline - these patients will not benefit from knee preservation and AKA may facilitate easier care
• Patients in persistent vegetative state or with severe stroke
• Patients with very short life expectancy

4. Special Considerations in Trauma

In severe limb trauma with hemodynamic instability: 1

• No single severity score (MESS >7, MESI >20) should mandate amputation in isolation - these scores have poor predictive value 1
• The level of amputation (BKA vs AKA) has major functional impact and should favor BKA when possible 1
• Ischemia time >6 hours increases reimplantation failure risk, but should be considered a relative rather than absolute criterion 1

Critical Pitfalls to Avoid

Common Error: Choosing AKA for "Better Healing"

This is outdated thinking. While historical data suggested AKA had better wound healing rates, modern wound care and prosthetic technology have changed this calculus. 4, 5 The functional superiority of BKA justifies accepting slightly higher revision rates. 2, 3

• Use of removable rigid dressings (RRD) after BKA dramatically reduces conversion rates to AKA (from 42.86% to 7.55% in one study), making BKA more viable 5
• Both BKA and AKA have similar mortality rates - the difference is in functional outcomes, not survival 4

Mortality Risk Factors (Not Level-Dependent)

Neither BKA nor AKA independently predicts mortality. 4 The actual mortality predictors are:

• Dementia (HR 2.769)
• Non-ambulatory status preoperatively (HR 2.281)
• Heart failure (HR 2.013)
• Renal failure (HR 1.87) 4

Reoperation Risk

Resistant bacterial infection (HR 3.083) is the primary risk factor for reoperation, not amputation level. 4

Post-Amputation Care Requirements

For patients undergoing BKA: 1

• Implement customized follow-up program including local wound care
• Provide pressure offloading strategies
• Serial evaluation of foot biomechanics (for minor amputations)
• Prescription therapeutic footwear to prevent wound recurrence
• Use removable rigid dressing as first-line post-operative care 5

Through-Knee Amputation Consideration

Through-knee amputation (TKA) offers an intermediate option that provides better physical quality of life than AKA, with similar ability to walk 500 meters as BKA. 2 However, TKA patients experience significantly more pain and wear their prosthesis less than AKA patients, creating a trade-off. 2 When BKA is not feasible, TKA should be considered before defaulting to AKA in ambulatory patients. 2

The Bottom Line

Preserve the knee whenever surgically feasible in patients with ambulatory potential. 1, 2 The functional benefits of BKA - including prosthetic use, independent mobility, and quality of life - far outweigh concerns about healing rates, especially with modern wound care techniques. 5, 2, 3 For non-ambulatory or moribund patients, AKA is acceptable and may facilitate care. 1