Preprocedural Evaluation
In patients with peripheral vascular disease (PVD), the diagnosis is usually known because these individuals have had extensive vascular studies and have most often undergone attempts at revascularization. With progressive small-vessel occlusion and neuropathy, toes become gangrenous and pressure points develop trophic ulcers, allowing bacteria to take hold and eventually invade the bone.
Throughout treatment, costly measures are undertaken in attempts to salvage a marginally viable extremity, with the patient losing valuable productive time. The patient has often undergone multiple foot amputations and multiple debridements and is often wheelchair-bound for pain relief or for relief of pressure on the extremity. Additionally, the patient often has an ascending cellulitis due to venostasis or constant pain due to ischemic disease.
For trauma patients, the amputation may be the result of direct limb transection or a severe open fracture with an associated unreconstructable neurovascular injury. The limb is so severely injured that reconstruction is less functional than an amputation. The other end of the spectrum includes an unsuccessful prolonged limb-salvage attempt that leaves the patient with a painful nonfunctional limb. The salvaged limb often requires a protracted course of treatment that takes a psychological toll on the patient and absorbs significant emotional energy. The resulting limb may be less functional than a prosthesis would have been.
Osteomyelitis may be the result of systemic disease or of open fractures. Cultures or biopsy can often be used to identify the infecting organism. Gas gangrene due to Clostridium species is a very serious infection, often resulting in amputation. Clostridial myonecrosis infections develop rapidly, and patients present with symptoms of pain, sepsis, and delirium. Examination on palpation often reveals a brownish discharge and crepitation within the soft tissues.
Streptococcal myonecrosis infections develop more slowly than clostridial infections. Persons with diabetes mellitus often develop polymicrobial infections that involve anaerobic gas-forming gram-negative organisms.
Malignancies often manifest with pain. The patient is often referred for amputation following a workup for a tumor, after limb salvage is excluded as an option.
Congenital limb deficiencies and malformations are evident and are present since birth. With growth, functional difficulties and limitations develop that limit the patient's mobility.
Vascular evaluation (eg, via pulse examination, ankle-brachial index [ABI], angiography, computed tomography [CT] angiography [CTA], duplex ultrasonography [US], or magnetic resonance angiography [MRA]) before major lower-extremity amputation is feasible in the majority of patients and allows evaluation for revascularization options before the operation. [26]
Laboratory studies
Amputation wound healing is a concern because most amputations are performed for compromised circulation. Standard laboratory studies are recommended, as are elective laboratory studies, depending on the patient's medical condition. Laboratory studies relevant to wound healing are as follows:
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C-reactive protein (CRP) - This inflammatory marker is an indicator of infection; a level lower than 1.0 mg/L indicates no infection, whereas a level higher than 8 mg/L indicates significant infection
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Hemoglobin - A measurement higher than 10 g/dL is required; oxygenated blood is necessary for wound healing
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Absolute lymphocyte count - A count lower than 1500/μL indicates immune deficiency and increases the possibility of infection
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Serum albumin level - A level of 3.5 g/dL or lower indicates malnutrition and a diminished ability to heal the wound
In patients with nonprogressive gangrene, inadequate physiologic conditions as determined by these laboratory studies should be optimized (eg, oral or intravenous (IV) hyperalimentation before amputation for malnutrition). When progressive infection or intractable ischemic pain is present, an open amputation can be performed and the soft tissues can be established later.
Imaging studies
Anteroposterior (AP) and lateral radiography of the involved extremity is obtained.
CT and magnetic resonance imaging (MRI) are performed for the patient's tumor workup or for osteomyelitis to ensure that the surgical margins are appropriate.
Technetium-99m (99mTc) pyrophosphate bone scanning has been used to predict the need for amputation in persons with electrical burns and frostbite. A 94% sensitivity rate and a 100% specificity rate have been reported in demarcating viable tissues from nonviable tissues.
Doppler US is used to measure arterial pressure; the area under the waveform is a measure of flow. In approximately 15% of patients with PVD, the results are falsely elevated because of the noncompressibility of the calcified extremity arteries. Doppler US has been used in the past to predict wound healing. A minimum measurement of 70 mm Hg is believed to be necessary for wound healing. The following values should be determined:
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Ischemic index (II) - This index is the ratio of the Doppler US pressure at the level being tested to the brachial systolic pressure; an II of 0.5 or greater at the surgical level is necessary to support wound healing
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ABI - The value at the ankle level is believed to be the best indicator for assessing adequate inflow to the ischemic limb; an index lower than 0.45 indicates that incisions distal to the ankle will not heal
Other tests
Transcutaneous oxygen pressure measurement is a noninvasive test that assesses the partial pressure of oxygen diffusing through the skin. This study can be applied to any area of intact skin and records the oxygen-delivering capacity of the vascular system. [27, 28] Transcutaneous oxygen pressure measurement is believed to be the most reliable and sensitive test for wound healing. Values higher than 40 mm Hg indicate acceptable wound-healing potential; values less lower 20 mm Hg indicate poor healing potential.
One study of transcutaneous oximetry reported an 88% sensitivity rate and an 84% specificity rate. [28] The pressure may be falsely low in areas of edema, cellulitis, and venous stasis changes.
Preprocedural Planning
An optimal residual extremity is covered with well-vascularized muscle, fascia, and skin. The skin is the most important tissue for healing of the amputation wound and should be handled with care. Careful assessment and handling of the soft tissues assists in creating a durable residual extremity that can withstand friction within the prosthesis. This allows a maximal limb-prosthesis interface that results in greater surface area for a force/stress distribution capable of end weightbearing.
The appropriate level must be planned preoperatively, with acknowledgment of the possibility that a more proximal level may be appropriate and that leaving the wound open for a staged procedure may also be appropriate. Decisions and adjustments are made on an intraoperative basis and planned for preoperatively. The options and possibilities are presented to the patient and family during the informed consent discussion.
Preoperative preparation includes the following steps:
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Appropriate preoperative antibiotics are administered in cases of infection, and prophylactic antibiotics are administered in cases of elective amputation or those resulting from trauma
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A tourniquet is placed on the limb prophylactically and used on a discretionary basis
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Vascular and bone instruments are requested
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A series of 45º chisels are obtained for osteomyoplastic reconstruction
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An appropriate strength saw for cutting bone is obtained (usually a power oscillating saw)
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Vessel ligatures are obtained
Monitoring & Follow-up
Two weeks after surgery, muscle-contraction exercises and progressive desensitization of the residual extremity are initiated. Desensitization is started with a towel for distal residual extremity pressure, and distal end bearing is started on a soft structure (usually a bed).
Prosthetic management is begun 6 weeks after surgery, depending on the condition of the extremity and wound. Some patients are not candidates for prosthetic limb replacement, because of poor balance, weakness, or cognitive impairment. To avoid disappointment and expense, a permanent prosthesis should not be ordered for these patients.
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Image that depicts the various levels of lower-extremity amputations.
Tables
Amputation level |
Energy above baseline, % |
Speed, m/min |
Oxygen cost, mL/kg/m |
Long transtibial |
10 |
70 |
0.17 |
Average transtibial |
25 |
60 |
0.20 |
Short transtibial |
40 |
50 |
0.20 |
Bilateral transtibial |
41 |
50 |
0.20 |
Transfemoral |
65 |
40 |
0.28 |
Wheelchair |
0-8 |
70 |
0.16 |
