Definition

The incidence of lower limb amputations due to vascular disease has increased in the United States by approximately 20% during the last decade, disproportionately in minorities [1]. Persons with diabetes mellitus and peripheral vascular disease should be identified and prophylactic foot education and preventive care instituted to reduce the risk of limb loss [2].

Diabetes mellitus, a multisystem disease, causes two conditions that place the foot at high risk for amputation: polyneuropathy and peripheral arterial disease (PAD). Diabetes affects about 25.8 million Americans [3]. Diabetes is also on the rise in the United States, particularly in African American and Hispanic populations [4]. Data from the Framingham Heart Study [5] revealed that 20% of symptomatic patients with PAD had diabetes, but the true prevalence of PAD in patients with diabetes has been difficult to determine as most patients are asymptomatic, many do not report their symptoms, screening modalities have not uniformly been agreed on, and pain perception may be blunted by the presence of peripheral neuropathy [6].

Risk factors for diabetic ulcers include male sex, hyperglycemia, and diabetes duration. Foot ulcers often result from severe macrovascular disease, and diabetic neuropathy exacerbates the risk [7]. More than 60% of nontraumatic lower limb amputations occur in people with diabetes, underscoring the need to prevent foot ulcers and subsequent limb loss [8]. Multidisciplinary clinics that identify and manage patients with at-risk feet have demonstrated impressive reductions of 44% to 85% in the incidence of foot ulcers and lower limb amputations [9]. Minor foot trauma in a person with poor underlying circulation and reduced sensation can lead to skin ulceration. Skin ulcers, if they fail to heal, may lead to gangrene and progress to a point such that an amputation becomes necessary. This sequence of events can often be prevented before it starts.

Numerous studies have further shown that attention to lifestyle modification can dramatically reduce progression to type 2 diabetes [10]. The importance of identifying and treating a core set of risk factors (prediabetes, hypertension, smoking, dyslipidemia, and obesity) cannot be overstated [11].

Atherosclerosis is a vascular disease that can involve the peripheral arterial system. PAD is underdiagnosed, undertreated, and increasing in prevalence [12]. The American Heart Association estimates that 8 to 12 million Americans have PAD and that nearly 75% of them are asymptomatic. Annually, approximately 1 million Americans develop symptomatic PAD [13]. Despite its association with other cardiovascular risks including stroke and heart disease, only 25% of Americans with PAD are undergoing active treatment [14]. Major risk factors associated with the development of PAD or that accelerate its progression are high plasma cholesterol and lipoprotein levels, cigarette smoking, hypertension, diabetes, hyperhomocysteinemia, older age, positive family history, and chronic kidney disease [15–17]. African American ethnicity is a strong and independent risk factor for PAD [8]. Hypertension is an important risk factor for PAD, conferring a twofold to threefold increased risk for development of PAD [18]. The risk of PAD is increased two to four times by diabetes [19]. Given that men have more risk factors for PAD, they are more commonly affected than women are.

Symptoms

The patient with a diabetic foot may demonstrate no symptoms because peripheral neuropathy can result in a lack of sensation. Peripheral neuropathy can mask painful ulcers and ischemic skin. Foot collapse due to Charcot joints can progress asymptomatically. Alternatively, diabetic patients can have pain sensations in the feet from sensory polyneuropathy, including burning, tingling, and painful numbness. Because of impaired sensation, patients may report imbalance and falls.

Persons with PAD have claudication pain with walking because of insufficient arterial blood supply to meet the demand of exercising muscles. Pain with vascular claudication is typically in the calf, worsened with ambulation and relieved by resting [20]. Symptoms of pain, ache, or cramp with walking can also occur in the buttock, hip, thigh, or calf [20]. Patients with neurogenic claudication due to spinal stenosis can have similar leg or calf pain with walking but must bend at the waist or sit to relieve the symptoms. Persons may present with gangrene, ischemic ulcers on the distal foot, or, when PAD is severe, pain at rest.

Physical Examination

In addition to a standard physical examination, special neurovascular areas must be highlighted [21].

Inspect the skin for ulcerations, cracks, callus, or trophic changes (thin, shiny skin; distal hair loss).

Evaluate for any foot deformities that predispose it to abnormal stress distribution. These include hammer toes, collapsed foot arches due to Charcot joints, high-arch feet due to intrinsic muscle atrophy from polyneuropathy, and changes in stress distribution from previous toe or ray amputations.

Assess distal pulses, particularly dorsalis pedis and posterior tibial. If they are absent or weak, it suggests the need for further testing for vascular integrity.

Assess sensation because persons with loss of protective sensation are at risk for skin ulceration. The instrument most frequently used for detection of neuropathy is the nylon Semmes-Weinstein monofilament. Inability to perceive the 10-g force applied by a 5.07 monofilament is associated with clinically significant large-fiber neuropathy [22].

Evaluate gait and balance. Peripheral neuropathy predisposes to falls and skin trauma. Probe any ulcers with sterile cotton-tipped applicators or surgical instruments. If bone is reached, this identifies persons with osteomyelitis, and other special bone imaging is unnecessary [23]. Assess shoes for uneven wear patterns, areas of breakdown, and width of the toe box.

Assess skin for redness and pressure points.

Functional Limitations

Persons with diabetes can develop peripheral polyneuropathy with loss of position sense and weakness. These can lead to gait instability and falls. Persons with PAD are often limited in community ambulation and vocational activities because of pain from claudication.

Diagnostic Studies

There are many noninvasive and invasive tests for PAD that are beyond the scope of this discussion. Angiography can identify surgically remediable lesions.

In the outpatient setting, the ankle-brachial index, a ratio of Doppler-recorded systolic pressures in the lower and upper extremities, is a convenient, accurate, noninvasive test that provides objective assessment of lower limb vascular status for screening and diagnosis of PAD [24]. Based on the results of the Ankle Brachial Index Collaboration, values above 1.40 indicate noncompressible arteries. Normal values are 1.00 to 1.40; borderline, 0.91 to 0.99; and abnormal, 0.90 or less [25]. The American College of Cardiology Foundation and American Heart Association Task Force on Practice Guidelines recommend resting ankle-brachial index to establish the diagnosis of lower extremity PAD in patients with exertional leg symptoms, nonhealing wounds, and age 65 years and older or 50 years and older with a history of smoking or diabetes [25]. Measurement of systolic pressure in the foot also provides a measure of arterial integrity.

Transcutaneous oximetry is the best method for assessment of cutaneous ischemia [9]. Transcutaneous oximetry pressures of more than 40 mm Hg are normal; pressures of 20 to 40 mm Hg indicate moderate disease, and potential for healing of a skin ulcer is less likely. With pressures below 20 mm Hg, severe skin ischemia is present, and skin healing is poor.

Systolic blood pressures in the foot are also helpful in quantifying the severity of ischemia. Persons with ischemic ulcers and ankle systolic pressures of less than 40 to 60 mm Hg are considered to have severe ischemia. Persons with persistently recurring ischemic rest pain and ankle systolic pressures of 50 mm Hg or less are severely involved [9].