Despite recent advancements in revascularization techniques, major lower extremity amputations remain commonly employed procedures with below knee amputations (BKA) being slightly more frequently performed than above knee amputations (AKA). Diabetes and peripheral arterial occlusive disease are the two most important contributing factors leading to major lower extremity amputation. Patients with diabetes are at an 8- to 10-fold increased risk in requiring an amputation. Increased age, renal function, and poor functioning status are also associated risk factors resulting in major lower extremity amputation. Because of the increasing burden of diabetes and the aging US population, the number of performed lower extremity amputations is expected to rise. The most common indications for a vascular surgeon to perform an AKA are acute limb ischemia, critical limb ischemia, dry/wet gangrene, failed prior amputation, and traumatic injury. Other less commonly seen conditions include malignancy and congenital malformations.

Acute limb ischemia requires an amputation in the setting of extensive irreversible tissue injury secondary to embolism or thrombosis of the arterial system of the leg. An AKA is indicated when the option for a more distal amputation is not feasible. Rapid progression of peripheral arterial disease from claudication to gangrene can also threaten limb viability. Patients who undergo failed revascularization attempts without remaining options will likely require amputation. In the setting of acute thrombosis, rhabdomyolysis can occur which may require staged (e.g., knee disarticulation with subsequent AKA) or urgent amputation to protect remaining renal function in patients with limited renal reserve.

Chronic limb ischemia is commonly seen in the elderly, diabetics, and chronic tobacco abusers. These patients have a large atherosclerotic disease burden and can have extensive arterial collateralization networks maintaining vital limb perfusion. The belief that most patients requiring an amputation secondary to critical limb ischemia progress from Fontaine stage I to stage IV before amputation is clinically unfounded. Nearly half of all patients undergoing a major lower extremity amputation for ischemia were asymptomatic 6 months prior to amputation. Even so, a number of these individuals will have had multiple failed revascularization attempts for claudication leading to progression to critical limb ischemia and tissue loss.

Critical limb ischemia can present with nonhealing ulcers, chronic ischemic pain, or severe infection with or without sepsis. It is usually a combination of factors which
can make these patients limited revascularization candidates. Patient factors including poor distal targets, lack of adequate conduit, poor functional status, multiple comorbidities, gangrene, and infection can all contribute to selecting amputation as definitive therapy.

Extensive gangrene and overwhelming infection may leave the surgeon with no other choice but to remove the limb. In the setting of severe infection, this can be seen as a life-saving procedure. In patients with active lower extremity infection, amputation is often best performed as a two-staged procedure with continued antibiotic treatments between stages. The initial procedure is a simple guillotine or knee disarticulation amputation followed by a formal revision to an AKA once the patient is medically stable. The need for revision of a BKA to an AKA can be necessary in as many as 25% of ischemic-related amputations, thus emphasizing the importance of a vigilant selection process for determining the proper amputation level. BKA revisions burden already at-risk patients with additional operative morbidity and must be avoided if possible.

Patients with pre-existing flexion contractions at the knee joint will almost certainly fail prosthetic training if a BKA is performed. Therefore, in the setting of a flexion contraction, removal of the knee via an AKA may provide the best chance for future ambulation. Generally, patients undergoing an AKA have a poor functional status with limited or no distal revascularization options. If physical findings and preoperative testing indicate a more proximal amputation is required, then a hip disarticulation may be required. When weighing the ability to tolerate anesthesia and surgery, the surgeon must be mindful that the patient’s ischemic limb may be contributing to their overall clinical deterioration.

Issues to address preoperatively include:

Patients undergoing elective amputations should have routine preoperative planning including cardiac evaluation if warranted, with rehabilitation consultation, psychological consultation if needed, and nutritional assessment. AKAs carry a significant morbidity with mortality rates as high as 25%. Specific risk factors for perioperative mortality include increased age, poor functional status, chronic pulmonary disease, congestive heart failure, dialysis, and leukocytosis. Optimizing a patient’s medical comorbidities should be attempted before proceeding with surgery. Correcting hemodynamic, metabolic, and electrolyte abnormalities preoperatively will help limit perioperative morbidity. Notable complications relating to the surgery include myocardial infarction, wound infection, renal insufficiency, and pneumonia. Without proper perioperative management, these conditions can contribute to poor postoperative outcomes.

While AKAs have a lower risk of reoperation than BKAs, the ambulation success rates are significantly worse. This is due to these patients’ worse overall clinical condition and the fact that the energy required to walk post AKA is 50% greater than if the knee joint is left intact. When considering an amputation for definitive treatment, it is
important to balance the desire to ambulate and maintain limb length with the goal of providing a successful outcome with the initial surgery. The primary purpose of a major amputation should be to remove all gangrenous and infected tissue while performing it at a level which will allow stump healing.

Selection of the appropriate level of amputation should be based on both physical findings and noninvasive studies. One should not replace a thorough clinical examination with objective test results, as these tests are not 100% predictive of success. While a palpable pulse proximal to the planned amputation level is a very good predictor for stump healing, the lack of a pulse does not guarantee failure and additional information must be ascertained. Clinical impression of function status and collected objective data should help determine the proper level of amputation. Individual patient factors and lower healing rates associated with more distal amputations may make an AKA the most appropriate initial level of amputation. Transcutaneous oxygen tension (TcPO₂) is commonly used with the understanding that systemic and local factors can lower the TcPO₂. These factors being a low PaO₂, diminished cardiac output, local edema, and cellulitis. Remember also that Ankle-Brachial Indices (ABI) may be falsely elevated in diabetic patients secondary to medial calcinosis.

Objective test result predicting wound healing at a level lower than AKA:

Early physical therapy evaluation may help augment preoperative functional status resulting in improved postoperative rehabilitation and ambulation. Studies have elicited several risk factors that predict failure to ambulate after major amputation including: inability to walk preoperatively, end-stage renal disease, dementia, >70 years old, coronary artery disease, homebound ambulatory status, and those undergoing an AKA.

Uncontrolled perioperative discomfort may increase the risk of a patient developing postoperative phantom limb pain. Adequate control of preoperative pain and epidural anesthesia in the postoperative period may help to reduce this risk. Regarding anesthesia type, no significant difference in mortality has been demonstrated when comparing general anesthesia versus regional nerve blocks, although it is the authors’ preference to avoid general anesthesia when possible, particularly in those with pulmonary compromise.

In septic patients with severe lower extremity infection requiring amputation for source control, a two-staged amputation is often required. The first stage involves a knee disarticulation or guillotine amputation (either transfemoral or transtibial) followed by a formal revision to closed amputation. The revision occurs once the patient’s sepsis is considered controlled, typically within 3 to 5 days.

Antibiotic and DVT prophylaxis must also be considered preoperatively. Prophylactic antibiotic use has been demonstrated to decrease postoperative wound infection rates in amputations of the lower extremity for ischemia. Antibiotic prophylaxis is typically with a cephalosporin such as cefazolin administered 60 minutes within time of incision. If MRSA is a potential pathogen, vancomycin is usually given. For pre-existing foot infections, consideration should be given for gram negative and anaerobic organism coverage. Many prescribe a three doses regimen of antibiotics, but others suggest a more prolonged 5-day course lowers postoperative infection rates and decreases length of hospital stay. Keep in mind that longer antibiotic courses are associated with an increased risk of Clostridium difficile infection. Given the increased incidence of DVT associated with major lower extremity amputation, DVT prophylaxis with heparin is usually administered preoperatively. DVT prophylaxis should be continued until mobilization is achieved postoperatively.

Finally, patients may develop depression due to the finality of amputation which may affect their postoperative course. If depression is a concern, then psychiatric consultation should be obtained immediately.

Because of the tenuous blood supply to the lower extremity in PAD patients, amputation begins with having an understanding of a few surgical concepts important to success. Careful attention should be addressed to the atraumatic handling of tissues. Limiting crushing injuries due to forceps and other instruments is important. Toothed forceps should be utilized while manipulating skin. Sharp dissection perpendicular to the tissue plane without undermining skin from fascia is critical. Electrocautery should be minimized and hemostasis achieved via ligation when feasible. All nerves should be transected sharply and allowed to retract into the stump away from weight-bearing areas to limit neuroma formation. Large nerves should be ligated with heavy silk. Femur and tissue flap length should be established prior to incision with emphasis on placing the stump scar on a non–weight-bearing area. Muscle and fascia should be placed between bone and skin to prevent scar retraction. Myopexy (suturing adductor and medial hamstring to periosteum), myoplasty (suturing adductor and medial hamstring to anterior muscle groups), or myodesis (suturing adductor and medial hamstring to distal bone via drilled holes) should be planned. Periosteal stripping should be limited and bone edges should be filed smooth. Flaps should be free of tension upon closing. Infected areas of limbs should be isolated prior to incision. All gangrenous and infected tissues should be removed. Strong consideration should be given to a two-staged guillotine approach for grossly infected limbs with sepsis.