What are the steps involved in performing an above-knee amputation?

Above-Knee Amputation: Surgical Technique and Measurements

The above-knee amputation (AKA) should be performed with the femoral bone cut approximately 12-15 cm (5-6 inches) above the knee joint line to optimize prosthetic fitting while preserving maximum functional length, using equal anterior and posterior myocutaneous flaps for optimal soft tissue coverage. 1

Pre-Operative Planning and Level Selection

Determining Amputation Level

• Measure 12-15 cm proximal to the knee joint line as the standard femoral transection point, balancing prosthetic fitting requirements with functional limb length 1
• Assess tissue viability at the proposed amputation site using:
  • Skin temperature >93°F at the amputation site predicts successful healing 2
  • Transcutaneous oxygen tension (tcPO2) >36 mmHg at mid-calf level indicates adequate perfusion for healing 2
  • Ankle pressure >50 mmHg or ankle-brachial index (ABI) >0.5 suggests sufficient vascular supply 3

Pre-Operative Considerations

• Initiate antibiotic prophylaxis immediately if performing amputation for infection, continuing for 48-72 hours post-operatively 3
• Ensure tetanus immunization status is current 3
• Start antiplatelet therapy pre-operatively unless contraindicated, continuing indefinitely post-operatively 3

Surgical Technique: Step-by-Step

Step 1: Skin Incision and Flap Design

• Create equal-length anterior and posterior myocutaneous flaps, each measuring approximately 50% of the limb circumference at the level of bone transection 1
• Mark the incision to allow 10-12 cm of soft tissue distal to the planned femoral cut to ensure adequate coverage without redundancy 1
• Design flaps to be slightly longer than the bone length to accommodate retraction during healing 1

Step 2: Muscle Division

• Divide muscles circumferentially at the level of the skin incision, preserving muscle length for myodesis 1
• Identify and ligate the superficial femoral artery and vein individually with non-absorbable sutures 1
• Isolate the sciatic nerve, pull distally under gentle tension, and transect sharply to allow proximal retraction away from the bone end 1

Step 3: Femoral Bone Transection

• Measure and mark the femur 12-15 cm above the knee joint line (or at the predetermined level based on tissue viability) 1, 2
• Use an oscillating saw to transect the femur perpendicular to its long axis 1
• Smooth and bevel the anterior edge of the femoral cut with a rasp to prevent sharp edges that could erode through soft tissue 1

Step 4: Myodesis and Soft Tissue Management

• Perform myodesis by drilling holes through the distal femur and suturing the adductor magnus and hamstring muscles to bone with non-absorbable sutures 1
• Suture the quadriceps muscle group anteriorly over the bone end to the posterior muscle groups 1
• This creates a stable, well-padded stump that tolerates prosthetic pressure 1

Step 5: Hemostasis and Wound Closure

• Achieve meticulous hemostasis before closure to prevent hematoma formation 1
• Consider tranexamic acid administration to minimize post-operative blood loss 3
• Place a closed-suction drain if significant dead space remains 1
• Close the deep fascia over the muscle without tension, then approximate subcutaneous tissues 1
• Close skin with interrupted or running sutures, avoiding excessive tension 1

Post-Operative Dressing and Management

Immediate Dressing Application

• Apply a removable rigid dressing (RRD) over soft dressings as the preferred method, rather than soft dressings alone 1
• RRDs provide multiple advantages:
  • Allow regular wound inspection 1
  • Reduce limb edema 1
  • Prevent knee flexion contractures 1
  • Protect the limb from external trauma 1
  • Facilitate faster healing times 1

Wound Monitoring

• Assess drainage daily for volume, character, and associated symptoms such as pain or fever 1
• Change dressings regularly using sterile technique to monitor wound status and maintain a moist wound bed while controlling drainage 1
• Implement a regular schedule for wound assessment to evaluate healing progress and identify early complications 1

Post-Operative Care and Rehabilitation

Thromboprophylaxis

• Initiate early pharmacological thromboprophylaxis with low molecular weight heparin (LMWH) after hemorrhage control and hemostasis 3
• AKA patients are at moderate-to-high risk for venous thromboembolism 3

Pain Management and Rehabilitation

• Monitor for neuropathic pain, which occurs in approximately 40% of AKA patients 4
• Begin physical therapy early with modifications to avoid excessive stress on the surgical site 1
• Note that only 45-50% of AKA patients will successfully be fitted with and use a prosthesis 4, 5

Critical Pitfalls to Avoid

Technical Errors

• Never create unequal flaps that result in a "dog ear" deformity or tension on the suture line 1
• Avoid transecting the femur too proximally, as this significantly impairs prosthetic function and patient mobility 3, 6
• Do not leave sharp bone edges, as these will cause skin breakdown and pain with prosthetic use 1

Wound Management Errors

• Never use superficial wound swabs for culture, as they are misleading and promote unnecessarily broad antibiotic treatment 1
• Avoid neglecting proper dressing selection, as soft dressings alone are inferior to RRDs 1

Clinical Decision-Making

• Consider knee disarticulation before AKA when feasible, as it preserves the femur completely, permits total end-bearing, and provides superior functional outcomes 6
• Recognize that AKA carries 28% two-year mortality compared to 4% for knee arthrodesis in infected total knee replacements, with age as an independent risk factor 4
• Understand that functional outcomes after AKA are poor, with most patients never achieving prosthetic ambulation 4, 5