Above-Knee Amputation and Hip Disarticulation

Robert J. Feezor and Thomas S. Huber

The incidence of major above-knee amputation (AKA) and below-knee amputation (BKA) has been relatively stable over the past few decades, with approximately 60,000 procedures per year performed in the United States. It is not clear that the widespread implementation of the endovascular therapies has favorably affected these rates, and this apparent paradox has been attributed to the aging population, the increasing incidence of diabetes and peripheral arterial occlusive disease (PAOD), the limited durability of the endovascular therapies, and the delays in presentation, among other factors. Most chapters on amputation highlight the fact that major amputations are among the most important procedures performed by vascular surgeons and therefore should not be relegated to the most junior members of the team; they are an important step in the rehabilitation process for patients with chronic limb ischemia, associated with the highest mortality rates of the elective vascular procedures; they are a treatment option rather than a failure of revascularization; and they have a major psychological impact on the patient. Although somewhat cliché, these common sentiments all merit consideration.

Above-Knee Amputation

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 (tcPO₂) 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.

Operative Technique

The operative technique for an AKA is fairly straightforward and has been well established. However, proper surgical technique with gentle handling of the tissues is paramount given the compromised state of the patient and tissue and the significant potential for wound complications. Both general and regional or spinal anesthesia techniques are appropriate, with the choice dictated by surgeon’s and anesthesiologist’s preference. Although the regional or spinal approach has been touted as safer from a cardiovascular standpoint in this high-risk patient population, the data supporting this contention has been somewhat equivocal. However, we have found these techniques beneficial in terms of postoperative pain control.

The choice of incision is dictated by the surgeon’s preference. We prefer a fish-mouth incision with equal-length anterior and posterior flaps because of the early cosmetic appearance (Figure 1). However, the circumferential incision and the fish-mouth incision with sagittal flaps are both acceptable. Notably, the muscle and other soft tissues atrophy and remodel during the early postoperative period so that the residual extremity looks essentially the same at 6 months regardless of the initial incision. The incision is usually made over the distal two thirds of the thigh in an attempt to preserve as much of the femur length as possible if there is any chance that the patient will walk on a prosthesis. The distal aspect of the anterior and posterior flap of the fish-mouth incision is commonly cited two finger breadths proximal to the patella, with the angle of the incision in the mid portion of the thigh, roughly 3 to 4 cm proximal to the most distal extent. The planned incision is marked on the skin, and then the anterior skin and soft tissues are incised along the planes of the skin mark.

FIGURE 1 The skin incision for an above-knee amputation using the equal length anterior and posterior fish-mouth technique is illustrated. The distal aspect of the incision on the anterior aspect of the thigh is a site approximately two fingerbreadths above the patella. The flaps are approximately 3 to 4 cm in length, and the femur is transected proximal to the angle of the fish mouth.

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Tags: Current Therapy in Vascular and Endovascular Surgery

Aug 25, 2016 | Posted by admin in CARDIOLOGY | Comments Off