What is BKA?
BKA stands for below-knee amputation, a surgical procedure where the lower leg is amputated at a level between the ankle and knee joint, preserving the knee joint itself. This is also referred to as transtibial amputation 1.
Clinical Context and Significance
BKA represents a critical level of amputation that offers significantly better functional outcomes compared to above-knee amputation. The preservation of the knee joint allows for:
- Superior mobility with prosthetics - Patients with BKA have substantially better chances of regaining ambulatory status and independent function 2, 3
- Lower energy expenditure during ambulation
- Better quality of life compared to higher-level amputations 4
When BKA is Performed
BKA is typically performed in several clinical scenarios:
Primary Indications
- Chronic limb-threatening ischemia (CLTI) when revascularization has failed or is not possible 5, 4
- Uncontrolled infection with necrosis or gangrene despite optimal management 4
- Severe trauma when limb salvage is not feasible 6
- Diabetic foot complications with extensive tissue loss 7
Timing Considerations
Secondary amputation should be performed when revascularization has failed and reintervention is no longer possible, or when the limb continues to deteriorate because of infection or necrosis despite a patent graft 5.
Critical Success Factors
Vascular Assessment
The most important predictor of BKA stump healing is patency of the profunda femoris artery (PFA). Studies show that patent PFA is present in 73% of healed stumps versus only 35% in those requiring revision to higher level 8. Consider profundoplasty before BKA if profunda flow is compromised 8.
Revision Rates
Approximately 20-23% of BKAs require revision to a higher level, most commonly above-knee amputation, primarily due to poor stump perfusion 2, 8. This underscores the importance of adequate vascular inflow assessment before the initial procedure.
Postoperative Management
Optimal Dressing Strategy
Removable rigid dressings (RRDs) should be used for postoperative management of BKA rather than soft dressings 1. Evidence demonstrates:
- Median healing time of 76 days with RRD versus 127 days with soft dressings (p=0.02) 1
- 58% of RRD patients ready for prosthetic casting at 60 days versus 38% with soft dressings (p=0.03) 1
- Accelerated limb volume reduction in first two weeks: 63.85% with RRD versus 34.35% with soft dressings (p=0.01) 1
- Reduced fall-related trauma to the residual limb - one study showed decrease in annual incidence of residual limb injury from 17% to zero after introducing RRDs 1
Mortality Risk Factors
Mortality after BKA in diabetic patients is substantial. Independent predictors of increased mortality include 7:
- Chronic kidney disease (OR 2.20)
- Albumin <2.95 g/dL (OR 2.85)
- WBC >13.8 × 10⁹/L (OR 1.63)
- Charlson Comorbidity Index >5.5 (OR 2.61)
Key Clinical Pitfall
Do not assume a BKA stump with chronic ischemia requires conversion to above-knee amputation. Infrainguinal bypass to revascularize a previously intact BKA stump that develops femoral-popliteal occlusive disease should be considered before revision to a higher level 2. This preserves the functional advantage of the knee joint.