Serious disease of the lower extremity may often prompt consideration of major limb amputation (below-the-knee or above-the-knee) for many patients with atherosclerosis, diabetes mellitus, and bony as well as soft tissue infections of the foot. Often it is a complex process that renders a portion of the foot infected or necrotic, and sometimes major amputation is considered when a more limited, distal amputation of diseased tissue will retain the potential for a weight bearing, functional extremity. Limited amputations for limb salvage include excision of one or more toes, ray amputations from the mid-metatarsal distally, and transmetatarsal or completed metatarsal amputation.
All who treat the distal lower extremity should gain an interest in limb preservation so that excision is considered only for those parts of the lower extremity that are necrotic, involved with ischemic related or synergistic infection, or otherwise associated with an inability to heal with a functional outcome. Certainly, cellulitis above the ankle, ascending lymphangitis, plantar abscess, and absent pulses do not absolutely require that the entire foot be amputated if it is otherwise viable. In such cases, ascending infection can be treated with intravenous antibiotics, necrosis can be treated through operative debridement and excision of distal parts, and healing can be allowed to occur. Preservation of all viable tissue is important, and appropriate infectious disease principles of aerobic and anaerobic culture with antibody sensitivity testing and appropriate choice of antibiotic therapy is essential. Whenever viable tissue is evident at the ankle or distally, studies to determine distant amputation levels should be considered.
Preoperative evaluations which can determine a safe amputation level within the confines of the foot have included transcutaneous oxygen mapping, distal Doppler pressure measurement, Doppler flow studies of the lower extremities, and lower extremity blood pressure determination. Angiography also may be suggested in some cases, but should generally follow a well designed non-invasive evaluation. Interestingly, physical examination remains one of the most sensitive tools which the clinician can apply to the ischemic, infected, or diabetic-neuropathic foot. The goal of examination and assessment is to determine preoperatively which site may be chosen for amputation in a manner which will allow painful, necrotic, and infected tissue to be removed with fair certainty that healing will follow.
The multidisciplinary approach to limb salvage cannot be overemphasized. Obviously, good blood glucose control for diabetics during the course of antibiotic therapy for infection should involve physicians expert in managing these two problems. Whenever non-invasive laboratory studies of the limb vasculature indicate an obstructive process, consideration that angiographic and possibly invasive imaging approach to occlusive lesions should be considered. Certainly, enlisting the expertise of peripheral vascular surgeons as well as podiatric physicians may best serve many patients. Since distal foot amputation is almost always considered for patients who have complex medical and surgical disease, several surgical and non-surgical specialists may be called upon to optimize care in the limb salvage effort.
Two studies from a single Veterans Administration Medical Center concluded that most efforts at salvage of the foot were successful, even if ascending cellulitis and absence of a distal pulse were noted. In one of the reviews, 101 patients initially treated with amputation of the distal foot averaged 61 years of age with 80% of the patients having diabetes mellitus, atherosclerotic vascular disease or both1. Other complicating diagnoses included hypertension, congestive heart failure, chronic renal insufficiency, or a combination of these factors. Due to bilateral disease, there were 124 initial amputation attempts in the 101 patients and 41 reoperative procedures to preserve the foot below the ankle; there was no surgical mortality. Healing failed when the primary or an associated diagnosis was atherosclerotic vascular disease or hypertension. In patients with a primary diagnosis of diabetes mellitus and without major vessel atherosclerosis, the majority of primary amputations were successful when surgeons resected to viable tissue. An important risk factor was disease in the contralateral extremity which was associated with ipsilateral failure in 27 of 45 patients (60%). Advancing age and race did not appear to be associated with a difference in outcome, nor was insulin requirement to control diabetes a factor which could be implicated in failure to heal.
The most significant feature accompanying successful outcome in distal foot amputation was the presence of any palpable pedal pulse. While microvasculopathy in diabetics can be associated with tissue ischemia in the presence of palpable foot pulses, the absence of a pedal pulse was associated with a 43% success rate compared with an 83% success rate when a distal pedal pulse was present. Success was achieved in 62% of cases when there was a palpable popliteal pulse, compared to 48% when the popliteal pulse was absent. Clearly, the well vascularized extremity, as noted on physical exam, can be expected to heal successfully after distal foot amputation. Cellulitis above the ankle was not predictable of outcome, so attempts to salvage the foot may proceed even in the face of ascending infection in some cases so long as there is resection of tissue in a stepwise fashion to viable, bleeding, non-necrotic tissue.
Of the 124 extremities studied in this review, 70 of the extremities required multiple amputations, 39 of these cases ultimately requiring above the ankle (major) lower extremity amputation. Frequent return to the operating room should be expected, and many cases in which reamputation or more cephalad revision of a distal foot amputation happens to be required ultimately heal with a functional foot.
A review of transmetatarsal amputation cases from the same center also emphasized the multifactoral etiologic nature of diseases eventuating in distal foot amputation, as well as the bilateral nature of this problem2. Once amputation fails at the transmetatarsal level, however, most subsequent operations are either below-the-knee or above-the-knee major amputations. The short-term mortality and long-term morbidity of patients ultimately requiring below-the-knee or above-the-knee amputation was notable.
A special circumstance occurs in the diabetic who has soft tissue infection of the foot3. While many of these infections are not associated with necrotic tissue, those associated with tissue necrosis must be approached surgically. The patient who presents with systemic sepsis (tachycardia, hypotension, fever, and organ dysfunction) as well as marked changes of the foot involving tenderness, crepitus, induration, or other signs of necrotizing infection may be a surgical emergency in the truest sense. Necrotizing infection, especially in the diabetic, can be overwhelming and can involve a host of organisms which cannot be irradicated until surgical debridement is completed. In such cases, patient evaluation should involve immediate plain x-ray examination of the extremity to ascertain the presence of gas within foot tissues, presence of any foreign body, or signs of osteomyelitis. While some have suggested either local probing or draining of infected wounds in the diabetic foot, the missed opportunity to debride a spreading necrotizing infection and salvage the extremity may not present itself again. Whenever infection is present, appropriate aerobic and anaerobic culture as well as tissue staining may be required. Complex synergistic infections of multiple organisms may involve the skin, fascia, muscle, and bone. Therefore, intraoperative exploration as soon as an operating room is available may salvage life and limb in many cases.
Appropriate antibiotic therapy in the infected diabetic foot should be instituted promptly and should take into account that the necrotic-infected foot requires broad spectrum empiric coverage initially4. A subsequent culture report may disclose one or more organisms which can be treated with a single antibiotic. Clearly, consultation with an infectious disease expert in situations involving limb salvage and infection would appear appropriate. Similarly, optimizing organ function for patients with multisystem disease and tightening blood glucose control in diabetics is advantageous.
Hyperbaric oxygen treatments have been advocated as a useful adjunct in certain types of infection and in cases of distal limb ischemia. The results of hyperbaric therapy can be dramatic in some cases, but almost always must be accompanied by aggressive surgical and antibiotic therapy as well since dead-infected tissue may serve as a medium for bacterial growth, toxin production, and adjacent tissue invasion in the presence or absence of a hyperbaric environment.
One of the most important features in the treatment of ischemic or diabetic foot is prevention. Many professionals recommend that the foot be cleansed regularly, that clean stockings and appropriate shoes be available, and that foot inspection-examination by the patient and someone else be carried out on a daily basis. Certainly, the patient with atherosclerosis or diabetes who is knowledgeable about self-examination can identify almost any lesion of the foot early. Early identification and intervention can prevent many of the progressive problems which ultimately require surgical care.
Preservation of limb function without endangering the patient must be a goal of treating ischemic, diabetic, and infectious problems of the lower extremity. When an extremity is encountered with ischemic or infectious changes, the questions regarding treatment relate to features that are known, visible, and palpable. A safe approach can incorporate the concepts that infection should be treated primarily with antibiotics, necrosis should be treated with excision, and ischemia should be addressed whenever feasible. The goal of preserving function of the lower extremity must always take into account the danger to the patient's life that the extremity may represent. Clearly, amputation of the distal portion of the extremity is safe in many patients and can result in a functional outcome. Once distal foot amputation is successful, rehabilitation with appropriate orthotic or prosthetic devices may allow years of a functional extremity, especially if the patient attends to preventive measures including smoking cessation, daily foot hygiene, and daily foot inspection. Patients must always be advised that the contralateral extremity is at risk and that the systemic nature of the disease process requires careful and daily attention to care and compliance with medical intervention.
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