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Amputations – Lower Extremity


Goals/Objectives

  • Basic Principles

  • Anatomy

  • Technical Considerations

Lower Extremity Amputation: General Considerations

Wayne W. Zhang
Ahmed M. Abou-Zamzam

From Cronenwett JL, Johnston KW: Rutherford's Vascular Surgery, 7th edition (Saunders 2010)

Addressing Associated Heart Disease

The evaluation of any potential amputee depends on the urgency of the intervention. In patients with acute ischemia, embolic disease directs the focus of the investigation toward embolic sources – most often cardiac. Any arrhythmias or recent myocardial infarction with ventricular thrombus must be investigated and addressed. Echocardiography and anticoagulation are key aspects of perioperative management. Preoperatively, however, the focus is on stabilizing an unstable patient. The nonviable limb should be amputated in a timely manner, with most diagnostic testing taking place in the postoperative period.

Patients with acute ischemia related to thrombosis of chronically diseased arteries have the same risk factors as patients presenting with chronic ischemia. In these patients, the role of extensive perioperative cardiac evaluation is unclear. Indeed, most reports of preoperative cardiac evaluation have excluded patients undergoing amputation, focusing instead on those undergoing aneurysm repair or lower extremity revascularization. Comparable perioperative mortality rates regardless of extensive preoperative cardiac evaluation call the practice of preoperative “cardiac clearance” into question. Guidelines issued in 2007 by the American College of Cardiology and the American Heart Association clarified that the purpose of preoperative cardiac evaluation is not to give medical clearance but rather to evaluate the patient's current medical status and cardiac risks over the entire perioperative period. These guidelines recommend that no test be performed unless it is likely to influence the patient's treatment.

Planning Rehabilitation

Throughout the perioperative evaluation, it is important to involve rehabilitation medicine specialists, physical therapists, nurses, and prosthetists in the care of these patients. Centers with dedicated multi­specialty teams have much more successful rehabilitation outcomes. Addressing the patient's concerns regarding postoperative recovery, the timing of prosthetic use, and ultimate functional goals is best done in the preoperative period.

Amputation Level Selection

The goals of amputation are (1) to eliminate all infected, necrotic, and painful tissue; (2) to have a wound that heals successfully; and (3) to have an appropriate remnant stump that can accommodate a prosthesis. The length of the preserved limb has important implications for rehabilitation. Prosthetic use following major amputation puts an increased energy demand on the patient. Unilateral below-knee amputees require a 10% to 40% increase in energy expenditure for ambulation, and above-knee amputees require 50% to 70% more energy to ambulate. This differential may explain why the successful rehabilitation rate is much lower following above-knee amputation (AKA) than below-knee amputation (BKA). Prosthetic use is reportedly 50% to 100% following BKA but only 10% to 30% following AKA. Interestingly, the true rate of ambulation is significantly lower than that of prosthetic use, and it shows a steady attrition in the 5 years following amputation. Partial foot or toe amputations are minor procedures that preserve the majority of the extremity and allow ambulation without the need for bulky prostheses. Most minor amputations, including toe and ray amputations, lead to minimal increases in energy expenditure and require simple orthotic inserts.

Failure of an amputation to heal is multifactorial. Much emphasis has been placed on assessing blood flow at the level of the amputation to predict wound healing. However, failure may be caused not just by ischemia but also by infection, hematoma, or trauma. This explains why no single test can predict with 100% accuracy the ability of an amputation to heal or, conversely, its inability to heal. Most tests are better at predicting wound healing than failure to heal. Thus, using any single test may lead to unnecessarily proximal amputation.

The importance of optimizing level selection is underlined by the need to revise BKAs to AKAs in 15% to 25% of patients. This revision rate is frequently accompanied by a perioperative mortality rate of greater than 5%. Such events also lead to increased patient anxiety and fear of repeated, more proximal amputations.

Objective Testing and Clinical Judgment

The drive to maximize limb length in amputees and to minimize the need for revisions has led to a search for the optimal modality for selecting an amputation level. Physical findings (pulses, skin quality, extent of foot ischemia or infection, skin temperature), noninvasive hemodynamic tests (segmental arterial pressures, Doppler waveforms, toe pressures), invasive anatomic tests (angiographic scoring systems), and physiologic tests (skin blood flow, skin perfusion pressure, muscle perfusion, transcutaneous oxygen measurements) have all been extensively investigated.

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