What are the steps of a below-knee (BK) amputation?

Below-Knee Amputation: Surgical Steps and Perioperative Management

Below-knee amputation should be performed using a standardized surgical technique that prioritizes preservation of tibial length while ensuring adequate soft tissue coverage, followed immediately by application of a removable rigid dressing rather than soft dressings to optimize healing and functional outcomes. 1

Preoperative Considerations

Patient Selection and Level Determination

• Determine the most distal amputation level that will heal and provide maximal functional ability through multispecialty team evaluation, as below-knee amputation offers significantly better functional outcomes and quality of life compared to above-knee amputation 1, 2
• Objective assessment using xenon-133 clearance studies can achieve 100% prediction accuracy for healing at the below-knee level 3
• Consider primary amputation only when life-threatening instability exists (severe infection, metabolic derangement, or ischemia causing systemic compromise) 1

Antibiotic Prophylaxis

• Administer antibiotic prophylaxis as soon as possible for open fractures or contaminated wounds, continuing for maximum 48-72 hours unless proven infection exists 1
• Use amoxicillin-clavulanate or cephalosporins as first-line agents; clindamycin plus gentamicin for beta-lactam allergies 1

Surgical Technique

Incision and Flap Design

• Create a long posterior myocutaneous flap to provide adequate soft tissue coverage over the tibial end 3, 4
• The posterior flap should be approximately one-third longer than the anterior flap to ensure tension-free closure 3
• Preserve maximum tibial length while ensuring adequate soft tissue padding, as longer residual limbs improve prosthetic function 1

Bone Division

• Divide the tibia approximately 12-15 cm below the knee joint (or at the most distal level with adequate soft tissue coverage) 3
• Bevel the anterior tibial crest to prevent pressure points under the prosthesis 3
• Divide the fibula 1-2 cm proximal to the tibial cut to prevent lateral prominence 3
• Smooth all bone edges meticulously to prevent skin breakdown 3

Vascular and Nerve Management

• Ligate major vessels (anterior and posterior tibial arteries, peroneal artery) individually with non-absorbable sutures 3
• Identify, gently pull down, and sharply transect nerves (tibial, common peroneal, saphenous) under tension so they retract proximally away from the weight-bearing surface 3
• This prevents painful neuromas in the residual limb 3

Muscle and Soft Tissue Management

• Create myodesis by securing the gastrocnemius-soleus muscle group to the distal tibia through drill holes or to the periosteum 3, 4
• This provides padding over the bone end and maintains muscle tension for better prosthetic control 3
• Ensure hemostasis is meticulous before closure to prevent hematoma formation 3

Wound Closure

• Close the wound in layers without tension, bringing the posterior flap anteriorly 3
• Place a drain if significant dead space exists, though this is controversial 3
• Use interrupted or continuous sutures for skin closure 3

Immediate Postoperative Management

Dressing Application

Apply a removable rigid dressing (RRD) immediately in the operating room rather than soft dressings - this is the single most important postoperative decision affecting outcomes 1, 2

Benefits of Removable Rigid Dressings

• Faster healing times and reduced limb edema compared to soft dressings 1
• Prevention of knee flexion contractures by maintaining the knee in extension 1
• Protection from external trauma and falls 1
• Preparatory contouring of the residual limb for prosthetic fitting 1
• Reduced pain and earlier prosthetic fitting 1
• Allows regular wound inspection (critical advantage over non-removable rigid dressings, especially for the 82% of patients with ischemic disease at high risk for wound dehiscence) 1

RRD Application Technique

• Apply the RRD over initial soft dressings 1
• Extend the rigid dressing to thigh level to splint the knee in extension 1
• Include a protective outer shell 1
• Ensure the dressing can be removed for wound inspection but provides consistent compression 1

Early Mobilization

• Allow the patient to stand with support at 1-2 days postoperatively when using rigid dressing techniques 4
• This early mobilization has significant psychological benefits and prevents deconditioning 4
• Non-weight-bearing RRDs are preferred over immediate postoperative prostheses (IPOPs) for most patients, as IPOPs carry risks of falls and inconsistent wound pressure, particularly in ischemic patients 1

Postoperative Medical Management

Antiplatelet Therapy

Initiate antiplatelet therapy immediately postoperatively and continue indefinitely unless contraindicated, as this improves graft patency and reduces cardiovascular events 1

Wound Monitoring

• Inspect the surgical wound regularly (advantage of RRD over non-removable dressings) 1
• Monitor for signs of infection, wound dehiscence, or hematoma formation 1, 2
• The 30-day complication rate includes 12.8% major complications and 8.7% minor complications 5

Risk Factors for Complications

Patients at highest risk for reoperation (9.6% overall rate) include: 5

• Recent smokers (34% increased risk) 5
• Bleeding disorders (30% increased risk) 5
• Patients transferred from another facility (28% increased risk) 5
• Preoperative ventilator dependence (138% increased risk) 5

Rehabilitation and Prosthetic Fitting

Timeline

• Reduce time to prosthetic fitting through use of RRDs, which decrease edema and prepare the limb for casting 1
• Optimal prosthetic fitting occurs when edema is controlled and the residual limb is properly shaped 1
• Immediate rigid dressing techniques can achieve 100% prosthetic rehabilitation rates in appropriate candidates 3

Long-term Outcomes

• Five-year survival rates: 75% for non-diabetic patients (approaching normal age-adjusted population), 39% for diabetic patients 3
• 75% of patients remain independently ambulatory on prostheses at five years when proper technique and immediate rigid dressing are used 3
• Preservation of the knee joint is critical - below-knee amputees have dramatically better mobility and quality of life than above-knee amputees 1, 2, 4

Common Pitfalls to Avoid

• Never use soft dressings alone - they are inferior to rigid dressings for virtually all outcomes (healing time, edema control, contracture prevention, pain, prosthetic fitting time) 1
• Avoid inadequate soft tissue coverage over the tibial end, which leads to wound breakdown 3
• Do not create excessive tension on the skin closure 3
• Avoid cutting the tibia too short in an attempt to ensure healing - preserve maximum length while ensuring adequate soft tissue 1, 3
• Do not use weight-bearing IPOPs in ischemic patients due to high risk of wound complications and falls 1
• Never delay antibiotic prophylaxis in contaminated cases 1