Above-Knee Amputation and Hip Disarticulation

Indications

The indications for AKA include acute limb ischemia, chronic limb ischemia, infection, trauma, and malignancy. The first three indications account for the overwhelming majority in most vascular practices. These indications are somewhat interrelated and often are complications of peripheral vascular disease and diabetes. Acute limb ischemia can lead to AKA in the presence of irreversible ischemia or severe tissue loss and/or for patients with no revascularization options or those with failed revascularization attempts. Chronic limb ischemia can lead to AKA for essentially the same indications, with the notable additions of patients with severe ischemic rest pain, patients whose BKA does not heal, patients who would not benefit from a BKA (i.e., no likelihood of ambulating with a prosthesis), or those with a nonuseable leg that would not benefit from attempts at revascularization and limb salvage (e.g., nonambulatory nursing home patient with a knee contracture). AKA can also be indicated for patients with extensive soft tissue infections or osteomyelitis not responsive to antibiotics.

The choice between revascularization and major amputation can be difficult. The data suggest that the mortality rate associated with major amputation exceeds that for revascularization. Although somewhat counterintuitive based upon the magnitude of the respective procedures, this observation likely reflects the inherent selection bias and the underlying comorbidities of the patients relegated to amputation. Nehler and colleagues provided a thoughtful, qualitative approach based upon the extent of tissue loss, the patient’s comorbidities, and the complexity of the revascularization, recommending amputation over revascularization if two of the three categories were extensive or severe (e.g., amputation for a patient with extensive tissue loss and severe comorbidities). It is important to emphasize that primary amputation is a better option for many patients and is clearly superior to multiple repeated attempts at limb salvage. Notably, delays in presentation, diabetes, end-stage kidney diseases, extensive tissue loss, and poor functional status have repeatedly been identified as predictors of primary amputation. It is worthwhile to consider the potential amputation incisions in this subset of high-risk patients at the time of attempted revascularization so that it does not compromise a later amputation should that become necessary.

The selection of the most appropriate major amputation level merits comment, similar to the decision about the choice of revascularization versus amputation. The common choice between an AKA and a BKA reflects an inverse relationship between wound healing and the rehabilitation potential or the likelihood of walking on a prosthesis. Although a variety of factors can affect wound healing, including blood flow, infection, and soft tissue injury, approximately 80% of all BKAs heal and 95% of AKAs heal. It has been estimated that it takes approximately 40% more energy expenditure to walk on a BKA prosthesis and 70% more energy to walk on an AKA prosthesis. From a practical standpoint, this translates into the fact that less than 10% will walk on an AKA prosthesis. Not surprisingly, advanced age, multiple comorbidities, dementia, end-stage kidney disease, advanced coronary artery disease, and nonambulatory status preoperatively have all been negatively associated with rehabilitation potential. Worldwide, the BKA-to-AKA ratio is approximately 1:1, although many patients who undergo BKA for complications of peripheral vascular disease or diabetes do not take advantage of walking on a prosthesis.

A variety of tests and techniques have been used to help predict whether an amputation can heal at a specific level, including simple pulse examination, hemodynamic measurements (e.g., blood pressure), anatomic assessment (e.g., arteriographic findings), and physiologic assessments (e.g., skin and muscle perfusion). Unfortunately, their overall predictive values are only fair, and they universally suffer from their inability to identify the lowest possible threshold value that predicts healing. The best predictor is likely an experienced clinician. Outside of an experienced clinician, a palpable pulse above the anatomic level of the amputation usually predicts healing (e.g., palpable femoral pulses predict AKA healing). Among the other assessment tools, the transcutaneous partial pressure of oxygen (tcP o ₂ ) is likely the most useful, with a value of greater than 30 mm Hg associated with healing.

Although the usual clinical decision is between a BKA and an AKA, a through-knee amputation is worth considering in younger patients with good rehabilitation potential. The longer limb length can provide some advantages in terms of walking speed and energy expenditure when compared to an AKA. The published experience with through-knee amputations is somewhat limited, although there is some suggestion that the wound complication rate may be higher. The earlier limitations of fitting a prosthesis at this level have been largely overcome.