What is the step-by-step surgical technique for a below knee amputation?

Below Knee Amputation: Step-by-Step Surgical Technique

The optimal below knee amputation technique involves creating a long posterior flap with the transection of the tibia approximately 12-15 cm distal to the knee joint to ensure adequate soft tissue coverage and optimal functional outcomes. 1

Preoperative Assessment and Planning

• Confirm that limb salvage is not possible due to advanced soft-tissue infection, severe tissue necrosis, failed revascularization with prohibitive pain, or non-reconstructable vascular disease 1
• Assess the optimal level of amputation based on infection extent, degree of ischemia, tissue loss, and healing potential 1
• Evaluate the patient's overall health status, comorbidities (especially diabetes), and potential for rehabilitation 1
• Obtain appropriate vascular studies to determine the optimal amputation level with adequate perfusion 2
• Administer prophylactic antibiotics prior to incision, especially in cases with infection 2

Surgical Technique

Step 1: Patient Positioning and Preparation

• Position the patient supine on the operating table 1
• Prepare and drape the limb in a sterile fashion, extending above the knee 1
• Apply a tourniquet at the thigh level if appropriate (contraindicated in severe peripheral vascular disease) 3

Step 2: Skin Incision and Flap Design

• Mark the anterior and posterior flaps, with the posterior flap significantly longer than the anterior flap 1, 3
• Begin the anterior incision approximately 10-12 cm below the tibial tuberosity 1
• Create a long posterior flap that extends distally to provide adequate soft tissue coverage 3, 4
• The ideal ratio is typically a posterior flap that is 2/3 the circumference of the leg at the level of bone transection 3

Step 3: Soft Tissue Dissection

• Incise through skin and subcutaneous tissue down to deep fascia 1
• Elevate skin flaps with subcutaneous tissue 1
• Identify and ligate the greater and lesser saphenous veins 1
• Divide the anterior and lateral compartment muscles at the level of the planned bone transection 1

Step 4: Neurovascular Management

• Identify, individually ligate, and transect the anterior and posterior tibial arteries and veins 1
• Identify, gently pull down, transect, and allow to retract the tibial, peroneal, and sural nerves to prevent neuroma formation at the weight-bearing surface 1, 3

Step 5: Bone Transection

• Transect the tibia approximately 12-15 cm distal to the knee joint using an oscillating saw 1
• Bevel the anterior edge of the tibia to prevent sharp edges 1, 3
• Transect the fibula 1-2 cm proximal to the tibial cut to prevent fibular prominence 1
• Smooth all bone edges with a rasp or file 1

Step 6: Muscle Management

• Secure the posterior muscle mass (gastrocnemius-soleus complex) over the end of the tibia using non-absorbable sutures through drill holes in the anterior tibia 1, 3
• This myoplasty technique provides cushioning for the bone end 3, 4

Step 7: Closure

• Place a closed suction drain if necessary 1
• Close the deep fascia over the bone end with absorbable sutures 1
• Close the subcutaneous tissue with absorbable sutures 1
• Close the skin with non-absorbable sutures or staples without tension 1, 3
• Apply a soft dressing or rigid plaster cast depending on surgeon preference 4

Special Considerations

• In cases of wet gangrene, a two-stage procedure with initial guillotine amputation followed by definitive long posterior flap amputation leads to better primary stump healing 5
• For very short proximal tibial stumps, consider a turn-up bone flap technique to lengthen the stump 6
• Ankle disarticulation can be used as a first-stage procedure in a staged approach to below knee amputation, especially in cases of infection 7
• The long posterior flap technique offers significant advantages in healing rates compared to other flap designs 4

Postoperative Management

• Begin early rehabilitation to maximize functional outcomes 2, 1
• Consider rigid plaster dressing followed by delayed application of a plaster cast and pylon 4
• Monitor for complications such as infection, hematoma, or wound dehiscence 1
• Initiate prosthetic fitting when the wound is healed and edema has subsided 1
• Provide comprehensive rehabilitation with physical therapy for gait training 1

Outcomes and Prognosis

• Below-knee amputations have significantly better functional outcomes compared to above-knee amputations 2, 1
• Primary stump healing rates are approximately 60% with the long posterior flap technique 5
• Walking with a prosthesis is associated with higher quality of life 1
• The surgical failure rate requiring revision to a higher level is approximately 4.2% 4