What is the procedure for performing a below knee amputation?

Below Knee Amputation Procedure

Below knee amputation (BKA) should be performed using anterior and posterior flaps with the posterior flap longer than the anterior flap, with the tibia transected 12-15 cm distal to the knee joint and the fibula cut 1-2 cm proximal to the tibial cut to ensure adequate soft tissue coverage. 1

Indications for Below Knee Amputation

• BKA is indicated when limb salvage is not possible due to advanced soft-tissue infection with sepsis, severe metabolic derangements from extensive tissue necrosis, failed revascularization with prohibitive pain, or non-reconstructable vascular disease 1
• Limb salvage should be attempted first in hemodynamically stable patients before considering amputation 1
• BKA offers better functional outcomes and quality of life compared to above-knee amputation, making it the preferred level when feasible 1, 2
• A multispecialty care team collaboration is essential for determining the optimal amputation level and achieving the best outcomes 1

Preoperative Considerations

• The optimal level of amputation should be determined based on:
  • Presence and extent of infection 1
  • Degree of ischemia and tissue loss 1
  • Potential for healing at the selected level 1
  • Patient's age, presence of diabetes, and other comorbidities 1, 3
• Risk factors for reoperation and complications include:
  • Recent smoking history 3
  • Bleeding disorders 3
  • Preoperative ventilator use 3
  • Transfer from another facility 3

Surgical Technique

Standard Approach

1. Create anterior and posterior flaps with the posterior flap longer than the anterior flap to ensure adequate soft tissue coverage 1
2. Transect the tibia approximately 12-15 cm distal to the knee joint 1
3. Transect the fibula 1-2 cm proximal to the tibial cut 1
4. Identify, ligate, and transect major vessels and nerves to prevent complications 1
   • Proper vessel ligation is critical to prevent bleeding complications
   • Nerves should be gently pulled down, cleanly transected, and allowed to retract to prevent neuroma formation at the weight-bearing surface

Alternative Approach

• In cases requiring a staged approach, ankle disarticulation can be considered as a first-stage procedure before definitive BKA 4
• Benefits of this approach include:
  • Rapid infection decompression 4
  • Minimized blood loss compared to traditional tibial osteotomy 4
  • Can be useful in patients with severe infection or compromised tissue 4

Postoperative Management

• Antibiotic prophylaxis should be administered and continued for 48-72 hours in cases with open fractures or infection 1
• Early rehabilitation should be initiated to maximize functional outcomes 1
• Postamputation support and management of diabetes and medical comorbidities are crucial for improving quality of life 1
• Monitor for complications requiring reoperation, which most commonly include:
  • Need for higher level amputation (28.7% of reoperations) 3
  • Wound debridement or secondary closure (25.6% of reoperations) 3
  • Revision of the leg amputation (10.32% of reoperations) 3

Special Considerations

• If vascular bypass is needed, autogenous vein grafts provide the best patency results 1
• Prosthetic grafts may be used if autogenous vein is unavailable 1
• Walking with prosthesis is associated with higher quality of life, emphasizing the importance of appropriate prosthetic fitting and rehabilitation 1, 2
• Below-knee amputees typically have higher functional demands than above-knee amputees, requiring more aggressive post-operative physiotherapy 5

Common Pitfalls and Caveats

• Inadequate soft tissue coverage can lead to wound healing complications and need for revision surgery 1, 3
• Improper bone length can affect prosthetic fitting and functional outcomes 1
• Failure to address vascular insufficiency can compromise healing 1
• Not all patients will successfully use a prosthesis after BKA, so careful patient selection is critical to ensure optimal functional outcomes 2
• The 30-day mortality rate following BKA is approximately 5.14%, highlighting the importance of careful patient selection and perioperative management 3