While certain clinical features are known to increase the risk for lower-extremity amputation, peripheral sensory neuropathy has been identified as the major risk for diabetic foot ulceration (8). Pecoraro et al. (9) placed peripheral sensory neuropathy in the face of unperceived trauma at the entrance to the pathway to ulceration and amputation (Fig. 66.1). The inability of a patient with diabetes to feel pain places him or her at significant risk for future foot problems. Knowledge of this condition and education on preventive measures are critical to the patient’s ability to avoid ulcerations. However, even with appropriate preventive measures, ulcerations will develop. Unperceived or unintentional trauma occurs that results in breaks in the skin and inoculation by bacteria.

Clinically significant peripheral sensory neuropathy can be detected by using a 128-millihertz (mHz) tuning fork and a 5.07 Semmes–Weinstein monofilament wire as screening tools to identify at-risk patients (10,11,12). While loss of vibratory sensation is the initial step in the development of clinically significant neuropathy, grading with a tuning fork is often a subjective exercise without scientifically established norms. A biothesiometer provides more objective documentation of a patient’s ability to perceive vibratory sensation. Clinical studies have determined a vibratory perception threshold of 25 mHz as identifying patients at risk for ulceration (13). This instrument, however,
is not readily available to the practicing clinician. It is used primarily in clinical trials where documentation of the degree of sensory neuropathy is important in stratifying groups.

The 5.07 (10 g) Semmes-Weinstein monofilament wire is an effective and inexpensive device to identify the patient at risk for foot ulceration. Several clinical trials have demonstrated that patients with diabetes who are unable to perceive this gauge of monofilament wire are at a statistically significant higher risk for development of ulceration than are patients who are able to detect the wire (12). Proper use of the wire requires application of the wire against the foot with enough force to gently bend the wire (Fig. 66.2). Inability to feel the wire implies lack of adequate protective sensation. By testing different sites on the foot, areas of insensitivity can be mapped and identified to the patient. These patients then must be educated on the significance of sensory neuropathy and the steps to preventing foot ulcerations. Regular evaluation by a foot care specialist is recommended for these individuals.

Formal nerve conduction studies in patients with diabetes have not been shown to alter treatment planning. Nerve conduction studies are rarely helpful or necessary for the evaluation of neuropathy. Many patients with type 2 diabetes have clinically significant neuropathy at the time of diagnosis, and nerve conduction studies will be abnormal in the majority of these patients.

Motor neuropathy can produce foot deformities that put the foot at risk for ulceration (Fig. 66.3). Loss of innervation of the
intrinsic musculature of the foot can lead to common foot deformities such as hammer toes, claw toes, and plantar-flexed metatarsals. Plantarly prominent metatarsal heads result in areas of high focal pressures that have been shown to increase risk for foot ulceration. Digital deformities can be irritated dorsally by shoe gear, resulting in corns or even ulcerations.

Autonomic neuropathy, although less common than peripheral sensory neuropathy, can also affect the feet. Most commonly, autonomic neuropathy affects local temperature regulation and the function of sweat glands. Loss of sweat production can lead to dry skin (14). Untreated this can lead to cracking and fissuring, especially in the heel, creating a portal of entry for bacteria.

Peripheral vascular disease by itself is responsible for only a small percentage of diabetic foot ulcerations. Only 15% of all diabetic foot ulcers are purely ischemic (15). However, arterial insufficiency can lead to nonhealing of ulcerations once they have developed. The single most important indicator of adequate perfusion is the presence of palpable pedal pulses. Additional clinical maneuvers to assess vascular status should include measurement of the venous filling time and evaluation for dependent rubor and pallor on elevation. The presence of a slowly or nonhealing ulceration in the face of absent pulses warrants further evaluation. This may be in the form of noninvasive arterial studies. Pulse volume recordings and the character of the distal pulses on Doppler evaluation (monophasic vs. triphasic) can provide valuable information on the patient’s ability to heal the ulceration. Although ankle-brachial indices (ABIs) are measured, they are of limited usefulness in the patient with diabetes. The ABIs often are artifactually elevated due to medial calcinosis of pedal vessels. Assessment of a patient’s ability to heal should not be based solely on this measurement. The presence of a nonhealing ulceration with clinical or objective evidence of arterial insufficiency warrants a prompt referral to a vascular surgeon (16).

The areas under the metatarsal heads are the most vulnerable areas for plantar ulcerations. These areas have been identified as having high focal pressures in patients with diabetes (17,18,19). A symptom of these high pressures is the presence of callus tissue under a metatarsal head. This most commonly results from plantarly prominent metatarsal heads, as occurs in the intrinsic minus foot and when the plantar fat pad atrophies (20,21). More recently, an association between limited joint mobility and high plantar foot pressures has been discussed as a risk factor for foot ulcerations (22,23). Other causes of high foot pressures include developmental foot deformities such as bunions, hammer toes, or rocker-bottom deformities from Charcot joint disease.

Quantitation of plantar foot pressures in the form of vertical load is possible with various computerized pressure-sensing equipment (24). These devices are expensive for most private practitioners and are most useful as a research tool. A Harris mat (ink-impregnated foil that demonstrates pressure points in static stance), however, is a simple, inexpensive tool that can be helpful in identifying areas of high plantar foot pressures.

As previously noted, several classification systems for grading ulcerations exist (6). Classification systems have two primary purposes: (a) to provide healthcare professionals with a common language to describe and understand common conditions, in this case diabetic ulcerations; and (b) to help direct the management and treatment of these conditions. While these are noble and useful purposes, there are also notable deficiencies in each of these grading systems. Some neglect the importance of ischemia, others are too complex to remember, and others are not completely applicable to diabetic ulcers but are more appropriate to pressure or decubitus ulcers. Nevertheless, for the purposes of this book, the Wagner classification has been selected for the discussion of ulcerations and their management, as it is the simplest, best known, and most widely used system. One should, however, by aware of its shortcomings. The Wagner classification system is based strictly on ulcer description and depth. It ignores the importance of ischemia and infection in determining the severity of the ulceration. In other words, although a Wagner grade 1 or 2 ulceration in a patient with adequate blood flow can often be managed with little to no complications, a similar condition in patients with poor perfusion can be a limb-threatening condition.